Symposium OrganizersValeria Tohver Milam, Georgia Institute of Technology
Harry Bermudez, University of Massachusetts, Amherst
Rajesh Naik, Air Force Research Laboratory
Marc Knecht, University of Miami
Symposium Support National Science Foundation
Royal Society of Chemistry
The Journal Nanoscale
OO2: Macromolecule Design Strategies for Bio-enabled Materials Systems
Tuesday PM, April 10, 2012
Marriott, Yerba Buena, Nob Hill BC
2:45 AM - *OO2.1
Genetically Encoded Stimulus Responsive Elastin-like Polypeptides: Applications in Drug Delivery
Ashutosh Chilkoti 1
1Duke University Durham USAShow Abstract
This talk will cover recent developments in my laboratory on the genetically encoded synthesis of stimulus-responsive recombinant biopolymers and their self-assembly into nanoparticles for drug delivery. In the first example, we designed a chimeric polypeptide that consists of two segments: an ELP segment that consists of (VPGXG)n repeats (where n ranges from 60-150) followed by a short (GGY)8 segment, and showed that attachment of multiple copies of a hydrophobic molecule at the Y position can impart sufficient amphiphilicity to the polypeptide and thereby drive its self-assembly into near-monodisperse nanoparticles with the attached hydrophobic small molecule embedded in the core of the nanoparticle. This is an interesting finding, because it appears that any molecule with a hydrophobicity that is greater than a threshold value appears to drive attachment-triggered self-assembly of the chimeric polypeptide into a nanoparticle. Because many cancer chemotherapeutics are insoluble hydrophobic small molecules with poor bioavailability, this approach of attachment-triggered encapsulation of small hydrophobic molecules into soluble nanoparticles has great utility to increase the solubility, plasma-half-life and tumor accumulation of cancer chemotherapeutics. As a specific example, I will show how conjugation of multiple copies of the cancer chemotherapeutic Doxorubicin (Dox) via a pH-sensitive linker to the end of an ELP spontaneously triggers ELP self-assembly into near-monodisperse micelles. These nanoparticles are ~40 nm in diameter, release drug at pH 5.0 (relevant to endo-lysosomal release), are taken up by cells, show subsequent localization of the drug to the nucleus, and are cytotoxic. Notably, these Dox-loaded nanoparticles have a four-fold higher maximum tolerated dose than free drug and induce near complete tumor regression in a murine cancer model following a single dose. In the second example, I will discuss diblock ELPs with a histidine-rich hydrophobic block to create pH-responsive nano-particles. We show that these systems self-assemble in response to three orthogonal triggers: temperature can be used to self-assemble the ELPBCs into micelles below physiological temperature, a drop in pH that corresponds to tumor pH leads to micelle disassembly, and addition of physiological concentrations of Zn2+ can further stabilize these micelles or alternatively can be used to trigger their self-assembly at lower temperatures with no adverse impact on their pH sensitivity. These pH-sensitive nanoparticles achieve a more homogeneous intratumoral spatial distribution than their pH-insensitive counterparts, indicating their potential as delivery vehicles of drugs or imaging agents to solid tumors. This family of self-assembling ELPs provides rich opportunities for application in biotechnology and medicine.
3:15 AM - OO2.3
Design of Multi-component Self-assembled Peptide Amphiphile Micelles for Treatment of Atherosclerosis
Laurie Beth Drews 1 Dan Krogstad 2 Matthew Tirrell 3
1University of California- Berkeley Berkeley USA2University of California- Santa Barbara Santa Barbara USA3University of Chicago Chicago USAShow Abstract
Atherosclerosis, a disease characterized by the development of plaques, is one of the major causes of cardiovascular disease, which continues to be a leading cause of death in the United States. The lack of non-invasive treatment options for atherosclerosis once a plaque has developed presents an opportunity to design a drug delivery vehicle that can deposit a drug of interest at the site of the plaque. In order to develop such a treatment, markers of atherosclerosis must be identified that distinguish plaques from healthy sections of arteries. Universal markers for atherosclerosis exist and provide a means for a targeted drug delivery approach. One such late stage marker is fibrin, which forms as part of the blood clotting process, and preliminary work shows that the peptide CREKA selectively binds to fibrin in in vivo models of atherosclerosis . Early stage targets are also being explored including cellular adhesion markers of inflammation present on the artery wall. Drug delivery vehicles are created using peptide amphiphiles as the building blocks to form self-assembled micelles. Micelles provide the ability to load a drug of interest into the hydrophobic core or hydrophilic corona, as dictated by the structure of the drug. Peptide amphiphiles are formed by conjugating a hydrophilic head group, formed from a targeting peptide, to a hydrophobic tail, such as an alkyl chain, generally 12-18 carbons in length. Spherical micelles formed through the conjugation of a peptide, such as CREKA, to a DSPE-PEG tail vary in the range from 10-20 nm in diameter as determined by dynamic light scattering and cryogenic transmission electron microscopy. Critical micelle concentrations (CMC) obtained are on the order of 10 uM. The role of the hydrophobic tail is also being investigated to determine the function it plays in increasing the stability of micelles when in contact with proteins commonly found in the body, such as albumin. Additionally, the incorporation of multiple targeting peptides provides a multifunctional vehicle capable of binding to both early and late stage markers of atherosclerosis. The ability to tailor the size of micelles using two targeting peptides combined in a mixed micelle conformation will be discussed. The presentation of multiple peptide targeting components in a single micelle is verified by FRET.  Peters, D, et al. Targeting Atherosclerosis by Using Modular, Multifunctional Micelles. PNAS. 2009; 106 9815-9819.
4:00 AM - *OO2.4
Rationally Assembled Multifunctional Materials
Oleg Gang 1
1Brookhaven National Laboratory Upton USAShow Abstract
A fabrication of nanomaterials with tailored and multifunctional properties requires ample abilities to arrange different types of functional nanoparticles into designed architectures. The assembly strategy based on bio-selective encoding of nano-components, e.g. with DNA, potentially offer a power of self-assembly and the design versatility. Although a significant progress was demonstrated in the area of DNA-mediated assembly, assembled structures typically contain only one type of particles. We developed a broadly applicable strategy for DNA functionalization of nanoparticles of different types. Our approach allows for assembly of multi-functional heterogeneous materials from such nanoparticles and their combinations. The detailed studies of these heterogeneous assemblies, clusters and ordered arrays, reveals, for example, that a significant modulation of optical properties of individual components can be achieved due to plasmonic and collective effects. Our findings and their applications to optical and bio-detection areas will be discussed. Research is supported by the U.S. DOE Office of Science and Office of Basic Energy Sciences under contract No. DE-AC-02-98CH10886.
4:30 AM - OO2.5
Exploring Locked Nucleic Acids as a Reversible Biomaterials Assembly Tool
Ngozi A. Eze 1 Valeria T Milam 1 2 3
1Georgia Institute of Technology Atlanta USA2Georgia Institute of Technology Atlanta USA3Georgia Institute of Technology Atlanta USAShow Abstract
Oligonucleotides hold great promise as a programmable biomaterials assembly and disassembly tool. Modified oligonucleotides, such as locked nucleic acid (LNA), have been of recent interest in physiological applications due to their superior nuclease resistance over DNA. LNA is the most promising nucleic acid analog due to its reportedly low cytotoxicity effects. Past work in this area has focused on reversing DNA-linked assemblies (in the absence of cells) through thermal denaturation steps. Previously, the Milam lab has reported studies using competitive hybridization events to disassemble DNA-linked particles under isothermal conditions. Here, we focus on programming the isothermal assembly and disassembly of LNA-linked colloidal particles. Initially, to drive LNA-mediated particle assembly, we employ short duplexes that are either 1) perfectly-matched or 2) contain a single, center mismatch. Certain parameters must be controlled to minimize nonspecific attractions between LNA-functionalized colloidal particles, including the surface duplex density and the number ratio of large and small particles. To induce LNA-mediated disassembly, longer, perfectly-matched target strands are added to drive competitive displacement of the lower-affinity, original partner strands. Confocal microscopy confirms substantial assembly for both perfectly-matched and mismatched cases. Flow cytometry results indicate that the perfectly-matched targets are more efficient at displacing the mismatched duplex strands than perfectly-matched duplex strands. This work demonstrates that LNA can be used to assemble and disassemble colloidal particles under isothermal and physiologically-relevant conditions.
4:45 AM - OO2.6
Tunable Release of Active Oligonucleotides from Uncrosslinked Gelatin Microspheres
Valeria Tohver Milam 1 James O Hardin 1 Alberto Fernandez-Nieves 1
1Georgia Institute of Technology Atlanta USAShow Abstract
We are investigating gelatin-based matrices for the temporary encapsulation, then release of active, short oligonucleotide stands. While most previous work has focused on using gelatin matrices with covalent crosslinks in which protease digestion triggers release of encapsulated agents, we are using uncrosslinked gelatin in order to preserve its relevant temperature sensitivity for biomaterials applications such as drug delivery. Following encapsulation of DNA, polyelectrolyte bilayers are deposited on the gelatin matrices to act as a temporary diffusion barrier and prevent premature escape of DNA. We found that this polymer coating typically hindered DNA release at room temperature, but promoted at least 5-fold greater release at 37 Â°C relative to the room temperature samples. DNA released from the gelatin matrices was quantified through subsequent hybridization events with polystyrene particles functionalized with the complementary partner sequence. These hybridization studies confirmed that the gelatin matrix does not appear to compromise subsequent duplex formation capabilities of DNA. Our first studies in this gelatin-DNA system involved the use of small uniform â?oblockâ? geometries as well as polydisperse microspheres to assess the role of the polyelectrolyte coating and gelatin matrix. More recently, however, we have employed a microfluidics-based processing approach to form large, monodisperse gelatin microspheres for DNA encapsulation. Overall, our studies indicate that these DNA-loaded, uncrosslinked gelatin carriers represent a promising system for triggered release of encapsulated oligonucleotides for a variety of bio-related applications.
5:00 AM - *OO2.7
Engineering DNA-based Materials Systems for Real-world Applications
Dan Luo 1
1Cornell University Ithaca USAShow Abstract
DNA plays a critical role in all living organisms as the carriers and also the regulators of genetic information. A myriad of enzymes have been evolved that can control and process DNA efficiently and elegantly. Our research focuses on using DNA as both genetic (bio) and generic (nano) materials: a combination of these two distinct but complementary aspects, i.e., biomaterial with nanomaterial, has enabled us to establish a variety of DNA-based materials systems that are specifically designed for real-world applications. More specifically, inspired by polymers, we have successfully created different topologies of DNA from which we have since developed dendrimer-like DNA, DNA-hydrogels, DNAsomes, and DNA-nanoparticle hybrid assemblies, all in bulk scale. With these novel DNA-based materials, we are exploring real-world applications in diagnostics, cell-free protein production, drug delivery, cell culture and novel optoelectronics. For more information, please refer to our relevant publications:
1. Nature Communications,accepted, (2011)
2. Chemical Society Reviews, in press, (2011)
3. Nature Nanotechnology, 6, 268-276 (2011)
4. Angew Chem Int Ed. 49, 380-384 (2010)
5. Nature Protocols, 4, 1759-1770 (2009)
6. Nature Nanotechnology, 4, 430-436 (2009)
7. Nature Materials, (Article) 8, 519-525 (2009)
8. Nature Materials, (Article) 8, 432-437 (2009)
9. Nature Nanotechnology, (Cover Article) 3, 682-690 (2008)
10. Nature Materials, 5, 797-801 (2006)
11. Nature Protocols, 1, 995-1000 (2006)
12. Nature Biotechnology, 23, 885-889 (2005)
13. Nature Materials, 3, 38-42 (2004)
OO3: Poster Session: Bio-enabled Materials Systems
Tuesday PM, April 10, 2012
Moscone West, Level 1, Exhibit Hall
6:00 AM - OO3.10
Rationally-designed Novel Self-assembling Peptide Building Blocks: Cyclic Peptide Ampiphiles
Sung-ju Choi 1 Yong-beom Lim 1
1Yonsei University Seoul Republic of KoreaShow Abstract
Self-assembled peptides have been well known as promising biomaterials and functionalizable nanomaterials. Peptides, as principle components of natural proteins, have the advantages such as biocompativity and specific structures by their sequences. Peptides have mostly been designed to have linear molecular configuration, like a single strand long chain. Peptide chains have played a role in self-assembly of peptide nanostructures. For the purpose of the control of self-assembly processes and structures, novel peptide building blocks are different from traditional linear configuration and expected to build up another nanostructures. Cyclic peptides are one of the self-assembly building blocks that have unique morphological features and more constrained property than linear peptides. Another useful building block for self-assembly is the amphiphile molecules. Conventional amphiphile molecules are possessing both hydrophilic and hydrophobic parts on two ends of molecules. In contrast, the hydrophobic and hydrophilic groups are located on two opposite faces in facial amphiphiles. We suggest novel self-assembly building block in which the these cyclic and facial properties are combined. Here, we have designed, synthesized, and investigated the structures and characteristics of the novel and functionalized self-assembling cyclic amphiphile peptides. This approach shows the characteristic nanostructure formations. These special structures have hollow spaces in the core site and it should be useful for the intracellular delivery system.
6:00 AM - OO3.11
In vitro Selection of Binding-activated Transducers for Selective Capture and Release of Molecules
Seung Soo Oh 1 Kory Plakos 1 2 Yi Xiao 1 2 H. Tom Soh 1 2
1University of California-Santa Barbara Santa Barbara USA2University of California-Santa Barbara Santa Barbara USAShow Abstract
The availability of molecules that can perform complex functions triggered by target binding would impact many important areas in biotechnology including targeted drug delivery, in vivo imaging, and in vitro molecular diagnostics. However, the use of directed evolution methods to generate such Binding-Activated Transducer (BAT) molecules has proven to be a significant challenge because the desired molecular function must be directly linked to the selection strategy. As a first step, we have previously reported a microfluidic selection strategy that can generate DNA aptamers that undergo large conformational changes upon binding to a protein target (S. S. Oh et. al., PNAS 2010). In this work, we report a significant advancement in the selection of BAT molecules wherein a small â?otriggeringâ? molecule (ATP, adenosine triphosphate) can activate a number of molecular functions of the transducer including 1) the release of a specific DNA sequence, 2) the release of a â?ocargoâ? molecule (ATMND, 5,6,7-trimethyl-1,8-naphthyridin-2-ylamine) and 3) the capture of a â?otargetâ? molecule (NMM, N-methyl mesoporphyrin IX). To isolate these BAT molecules, we first designed a DNA library that incorporates both the pocket sequence to hold the cargo molecule as well as the inactivated DNAzyme sequence that capture the target molecule. We then performed microfluidic selections, which efficiently isolate the BAT molecules for the aforementioned functions. After 10 rounds of selection, we identified 3 DNA sequences that exhibit high affinity to ATP (Kd = ~20 Î¼M). Importantly, we confirmed that these BAT molecules, upon binding to ATP, indeed transduce the release of ATMND and the capture of NMM through fluorescence measurements.
6:00 AM - OO3.12
Profiling and Characterization of Silver, Zinc Oxide and Silver/ Zinc Oxide Hybrid Nanoparticles for Antimicrobial and Antifungal Properties
Vijaya K Rangari 1 Myisha Myisha Roberson 1 Clayton Yates 1 Temesgen Samuel 1 Shaik Jeelani 1
1Tuskegee University Tuskegee USAShow Abstract
Bio-compatible surface modified nanomaterials are known to be less cytotoxic to cells and more effective in therapies at lower dosages. Nanoparticles such as iron oxide, silver, gold and zinc oxide, etc are well known in the literature as minimum to non-toxic materials for healthy cells. They can be used as therapeutic drug, or drug carrier systems. In this study we have synthesized the ZnO, Ag and ZnO/Ag hybrid nanoparticles using microwave synthesis method and tested for their wound healing properties. These nanoparticles are susceptible to infection, induces cellular proliferation, increases skin penetration rate and cellular migration that allow the wound healing process to proceed toward a more regenerative pathway. The as-synthesized nanoparticles were characterized using X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) techniques to study the crystalline structure, composition, particle size, morphology and purity. Standard disk diffusion assays were used to study the antibacterial and/or antifungal properties of as prepared nanoparticles. Results shows that the Ag, ZnO and ZnO/Ag nanoparticles have antifungal and antimicrobial properties that potentially decrease susceptibility of a fungal or bacterial infection in a healing wound at minimum concentration of 50 Âµg/mL. Key words: Ag/ZnO hybrid nanoparticles, antimicrobial, antifungal, wound healing
6:00 AM - OO3.13
Microtubule Mimicry: Toward Biomolecular Self-assembly in Synthetic Materials
Dara Gough 1 Jill Wheeler 1 Bruce Bunker 1 Erik Spoerke 1
1Sandia National Labs Albuquerque USAShow Abstract
Microtubules (MTs) are dynamic supramolecular protein nanofibers that facilitate and direct a host of complex biological processes in cells ranging from chromosome separation during cell division to regulating cellular morphology and the trafficking of intracellular cargo. Creating synthetic analogs to MTs would present opportunities for advanced nanomaterials assembly and adaptable materials development. But creating these analogs requires a detailed understanding of the principles governing MT form and function. In this presentation, I will describe the use of wedge-shaped peptide dendrimers, designed to mimic key characteristics of a microtubuleâ?Ts natural tubulin building blocks. Guided by molecular dynamics simulations, these dendrimers contain characteristics such as electrostatic charge, hydrogen bonding, and amphiphilicity. By synthetically tuning these variables, we aim to reproduce characteristic influences on tubulin assembly including balance of lateral and vertical interactions of tubulin, molecular asymmetry, and supramolecular programmability. This supramolecular platform is a powerful tool for study of the critical factors that may lead to synthetic materials with the diverse, dynamic, and adaptable functions seen in natural microtubule systems. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
6:00 AM - OO3.15
Hybrid Configurations of Lipid Membranes with Plasmonic Nanoparticle Arrays
Theobald Lohmueller 1 Paul Kuehler 1 Jochen Feldmann 1
1LMU Munich Munich GermanyShow Abstract
Bilayers of phospholipid molecules display a high level of lateral mobility while covering the underlying substrate. Due to these unmatched characteristics, supported membranes feature unique capabilities to mimic biological surfaces and dynamic cellular processes that involve lateral mobility and movement of receptors. Noble metal nanoparticles and nanostructures on the other hand can impose obstacles to the mobility of molecules in this otherwise fluid environment. These particles furthermore exhibit extraordinary optical properties that offer a broad range of useful applications for plasmonic sensing and spectroscopy if they are properly harnessed. We demonstrate the fabrication and characterization of large-scale hybrid nanoparticle/supported membrane configurations that are built up by immobile arrays of plasmonic nanoparticles and nanoantennas embedded within a fluid supported membrane. Merely bottom-up nanofabrication methods are employed to control the size and spacing of billions of gold particles and triangles on one single substrate with nanometer precision. Subsequently, a supported membrane is assembled over the bare substrate in between the nanopattern. Fluorescently labeled ligands can be bound to the fluid lipid component, the nanoparticle component, or both, providing a hybrid configuration consisting of mobile and immobile ligand molecules with controlled geometry. Finally, we discuss how the intriguing properties of this innovative hybrid biomaterial platform can be used for sensing applications and surface-enhanced Raman spectroscopy.
6:00 AM - OO3.17
Manufacturing Anisotropic Eco-capsules and Its Assembly
Milana O Lisunova 1 Andrey Dorokhin 1 Neal Holland 1 Vladimir V Tsukruk 1
1Gatech Atlanta USAShow Abstract
Anisotropic capsules based on sodium chloride cubic cores were synthesized by layer-by-layer (LbL) assembly of the hydrogen-bonded polymers from the anhydrous alcohol solutions. A nonhazardous core release by water has been used. The overall thickness of these LbL shells with four bilayers is within 20 nm in dry state which is twice higher than for the LbL shells produced from the aqueous solutions. The cubic capsules as was observed mainly forms the highly compacted 3D cubic arrays due to the face to face interactions and steric confinements in sharp contrast to the assembly built by the spherical capsules for which the hexagonal packing is generally favored. The assembled spherical microcapsules create a large number of openings with extensive surface areas while the cubic microcapsules build close, compact aggregates. Thus the porosity of the cubic microcapsules assembly is mainly caused by the nano-porous shells which can be tuned by solvent composition (dielectical constant, pH).
6:00 AM - OO3.18
Apatite Coating on Hydroxyapatite/Collagen Nanocomposite Membrane for Surface Functionalization
Subhadip Bodhak 1 Masanori Kikuchi 1 Ayako Oyane 2 Yu Sogo 3 Hideo Tsurushima 4 Atsuo Ito 3
1National Institute for Materials Science Tsukuba Japan2National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Japan3National Institute of Advanced Industrial Science and Technology (AIST) Tsukuba Japan4University of Tsukuba Tsukuba JapanShow Abstract
The development of biomaterials applicable to tissue engineering technology has recently focused on the surface functionalization that can promote tissue regeneration. A biomimetic apatite coating is an effective technique for surface functionalization of biomaterials, since apatite can be incorporated with biomolecules including plasmid DNA and growth factors (BMP-2, FGF-2). The objective of our research is to develop an efficient coating technique for hydroxyapatite and collagen (HAp/Col) nanocomposites. The HAp/Col nanocomposites have the potential as bone substitutes due to their similar composition, nanostructure, and biological properties to those of human bone . The HAp/Col nanocomposites membrane samples were synthesized by the simultaneous titration method using Ca(OH)2, type-I atelocollagen and H3PO4 as starting precursor materials . Two different coating solutions, so-called CP solution  and RKB solution  have been investigated to deposit an apatite layer on the sample surface. The CP solution (NaCl 142 mM, CaCl2 3.75 mM, K2HPO4.3H2O 1.50 mM, buffered to pH=7.40 at 25 oC) was prepared using reagent grade chemicals . The sample was immersed in 3 ml of the CP solution at 25 oC for 24 hours after precoating with amorphous calcium phosphate (ACP) by three times alternate dipping into CaCl2 and K2HPO4.3H2O solutions . The RKB solution was prepared by mixing clinically available infusion fluids; Ringerâ?Ts solution (calcium solution), Klinisalz B (phosphate solution), and Bifil (alkalinizer) .The sample was immersed in 2 ml of the RKB solution at 37oC for 2 days. After coating in the CP solution, no apatite deposition was found on the sample surface as confirmed by scanning electron microscopy (SEM). A bioresorbable and highly unstable HAp/Col surface might inhibit the heterogeneous nucleation of apatite at the sample surface. In contrast, after coating in the RKB solution, micro-sized particles of apatite were deposited on the sample surface. It is considered that apatite particles were first formed in the RKB solution by homogeneous nucleation, grew into larger particles, and then deposited on the sample surface. It was found that apatite coating technique using the RKB solution was effective for the HAp/Col nanocomposites, whereas that using the CP solution was not. Functionalization of HAp/Col nanocomposites would be possible by using the RKB solution supplemented with biomolecules. References:  Kikuchi et al., Biomaterials 2001; 22: 1705-11.  Oyane et al., Acta Biomater. 2011; 7: 2969-76.  Mutsuzaki et al., J. Biomed. Mater Res. B 2008; 86B: 365-74. Acknowledgements: Authors would like to acknowledge the financial support from Japan Society for the Promotion of Science (JSPS)postdoctoral fellowship.
6:00 AM - OO3.19
Building of Hierarchical Zinc Oxide Nanostructures on a Biological Template
Chung Hee Moon 1 Steven Garcia 2 Elaine D Haberer 1 3
1University of California-Riverside Riverside USA2University of California-Riverside Riverside USA3University of California-Riverside Riverside USAShow Abstract
ZnO is a direct, wide-bandgap semiconductor which has proven useful for many electronic and optoelectronic applications in both bulk and nanocrystalline forms. Bio-directed synthesis of ZnO is a promising technique capable of morphological control under generally mild, low temperature conditions. Several ZnO-binding peptides have been reported, and a few have been further investigated for biomineralization purposes [1-3]. Such studies have focused on free peptides or peptides arranged on a planar surface. Here we report the biomineralization of ZnO on an M13 bacteriophage template. The highly ordered viral protein coat acts as a three-dimensional scaffold for the ZnO-binding peptides producing a hierarchical structure unavailable to isolated peptides in solution. The added organization of the template dictates the size, shape, and morphology of the resulting semiconductor material. A reported peptide sequence (EAHVMHKVAPRP) with a high affinity for ZnO was used to biomineralize ZnO using a Zn(OH)2 precursor solution . To explore cooperative effects caused by proximity and ordering during nucleation and growth, the peptide was fused to either the M13 minor coat protein or the M13 major coat protein using genetic modification or a sulfo-SMCC conjugation, respectively. The 3-5 copies of the minor coat protein located at the tip of the virus are highly flexible and possess only minimal long range organization. In contrast, the 2700 copies of the major coat protein located along the length of the virus have significant long range order. Transmission electron microscopy was used to examine the nanocrystal size and size distribution, geometry, morphology, and crystalline structure of the mineralized material. Further investigation of the crystal structure and material composition was completed with x-ray diffraction and energy dispersive x-ray spectroscopy. The optical properties of the bio-templated nanocrystalline ZnO were characterized using photoluminescence and absorption measurements. The relative intensities of the band edge and defect emission peaks were evaluated, as well as the width of the band edge emission peak. The hierarchical structure created by the viral template controls both the structure and properties of the resulting ZnO nanomaterials.  M. Umetsu, et. al., Adv. Mater. (2005) 17, 2571-2575;  M. M. Tomczak, et. al., Acta Biomater. (2009) 5, 876-882;  Z. Huang et. al., J. Colloid. Interf. Sci. (2008) 325, 356-362
6:00 AM - OO3.2
Biomimetic Synthesis of Pd Nanoparticles for Energy Efficient Catalysis
Dennis B Pacardo 1 Joseph M Slocik 2 Rajesh R Naik 2 Marc R Knecht 1
1University of Miami Coral Gables USA2Air Force Research Laboratory Wright-Patterson Air Force Base USAShow Abstract
Rapid environmental degradation and exhaustion of limited resources caused by processes that fuel technological advancements require the development of new materials that function more efficiently and operate under energy-neutral and eco-friendly conditions. This multi-pronged approach in green chemistry includes the need to efficiently produce materials and the necessity of reducing waste and production costs. We have demonstrated this approach by utilizing the Pd4 peptide in the synthesis of Pd nanoparticles for the Stille coupling reaction. This unique peptide, isolated via phage display, specifically recognizes fcc Pd and binds to the surface of growing materials in solution to generate peptide-capped Pd nanoparticles. These materials were used as catalysts for the coupling reaction between different aryl halides and organostannane reagents in aqueous solution at room temperature giving quantitative product yields using ultra low catalyst loadings (>0.001 mol% Pd). The catalysts are insensitive to reagent functional groups, are reactive for both electron withdrawing and donating aryl halides, and are selective to produce the new C-C bond. As a model system for green catalysis, it is essential to determine the catalytic mechanism driven by the peptide-capped Pd nanoparticles in order to optimize their efficiency by providing critical information regarding the structure-function relationship. By monitoring the turnover frequency (TOF) of the reaction at different catalyst loading, the results suggest an atom leaching mechanism is at work where the initial oxidative addition step at the nanoparticle is able to abstract Pd species from the surface, which was confirmed using a unique quartz crystal microbalance analysis.
6:00 AM - OO3.20
Nanoparticle Biotemplating at Two Distinct Epitope Sites at a Protein Interface
Kelly Noell Huggins 1 Alia P Schoen 1 Manickam A Arunagirinathan 1 Sarah C Heilshorn 1
1Stanford University Stanford USAShow Abstract
Biotemplating is a unique synthetic route that provides an attractive â?ogreenâ? strategy for the potential manufacture of nanomaterials for electronic devices and energy technologies. Protein scaffolds, in particular, offer an infinite number of structural scaffolds with multiple exposed sites that can interact with the inorganic material. However, most protein biotemplates involve chemical or genetic modifications to the protein interface in order to interact with the inorganic material of interest. To extend the flexibility of protein biotemplates, we have established a unique biotemplating strategy that allowed us to successfully functionalize protein assemblies to template inorganic material using site-specific, non-covalent interactions without chemical or genetic modifications. The protein used in our study, clathrin, is a self-assembling intracellular protein that plays a major role in the transportation of cargo across the plasma membrane. Clathrin has proven to be a flexible biotemplate, forming stable assemblies in vitro that are analogous to in vivo 2D hexagonal lattice and 3D cage structures. Our previous studies have incorporated the â?oclathrin-boxâ? or "C-box" epitope sequence into the design of bi-functional peptides in order to mimic the non-covalent, heterogeneous protein-protein interactions that occur in vivo between adaptor proteins and clathrin. The bi-functional peptides combine the C-box recognition sequence upstream of inorganic-binding sequences, creating a molecular link between the clathrin protein interface and inorganic material. This strategy has been named Template Engineering Through Epitope Recognition, or TEThER, and facilitates a variety of inorganic materials to interface with the clathrin protein without modifying the protein assembly. The success of this strategy was previously illustrated through the biotemplated synthesis of three different inorganic particles: titanium dioxide, cobalt oxide, and gold. In the current study, we prove the flexibility of the TEThER strategy by introducing the use of a second, distinct epitope site on clathrin, the "W-box". The W-box epitope binds a conserved tryptophan-rich region of select adaptor proteins and is located a site distinct from the C-box. We illustrate the versatility of our protein biotemplate by synthesizing gold and titanium dioxide nanoparticles using the distinct W-box epitope site. We also extend the use of the TEThER strategy to demonstrate successful synthesis of platinum nanoparticles using either the C-box or W-box epitopes. These experimental results present the possibility of future heterogeneous nucleation of multiple inorganic materials on a single protein biotemplate with site-specificity for each inorganic species. We conclude that the TEThER strategy is a versatile and modular platform for biotemplating reactions.
6:00 AM - OO3.21
Antimicrobial Properties of a Zinc - Releasing Bioceramic
Xin He 1 Thomas Burr 2 Yizhi Meng 1 3
1State University of New York- Stony Brook Stony Brook USA2Cornell University-NYSAES Geneva USA3State University of New York- Stony Brook Stony Brook USAShow Abstract
Up to 80% of nosocomial infections are caused by biofilm-producing bacteria such as Staphylococci and Pseudomonas aeruginosa. These types of microorganisms can become resistant to antibiotics and are difficult to eliminate. As such, there is tremendous interest in developing bioactive implant materials that can help to minimize these post-operative infections. Using water-based chemistry, we developed an economical, biodegradable and biocompatible orthopaedic implant material consisting of zinc-doped hydroxyapatite (HA), which mimics the main inorganic component of the bone. Because the crystallinity of HA is typically too compact for efficient drug release, we substituted calcium ions in HA with zinc during the synthesis step to perturb the crystal structure. An added benefit is that zinc itself is a microelement of the human body with anti-inflammatory property, and we hypothesized that Zn-doped HA is an inherently antibacterial material. All HA samples were synthesized by a co-precipitation method using aqueous solutions of Zinc nitrate, Calcium Nitrate, and Ammonium Phosphate. SEM/EDS and XRD data showed that Zn was successfully incorporated into the HA. The effectiveness of Zn-doped HA against a model biofilm-forming bacterium is currently being evaluated using a wild-type strain and a streptomycin-resistant strain of Pseudomonas syringae pv. papulans (Psp) which is a plant pathogen isolated from diseased apples.
6:00 AM - OO3.22
Temperature-responsive Hydrogels with Improved Swelling and In Situ Crosslinking for Aneurysm Embolization
Elizabeth J Lee 1 Derek J Overstreet 1 Brent L Vernon 1
1Arizona State University Tempe USAShow Abstract
Introduction: Rupture of intracranial aneurysms is a devastating and potentially lethal health event, and current techniques for filling these aneurysms lead to high recurrence. A promising alternative is the use of liquid materials which can be injected and then become solid within minutes, blocking blood flow into the aneurysm. Smart materials such as copolymers of N-isopropylacrylamide (NIPAAm) may be useful for embolization due to their lower critical solution temperature (LCST) in water, forming a physical gel when heated above the LCST (~ 30Â°C). However, purely physical gels of poly(NIPAAm) are prone to deswelling and creep. Here, we report on an improved copolymer system for embolization which crosslinks by in situ reaction above the LCST and transitions from liquid to solid with almost no volume change. The material is a copolymer of NIPAAm, Jeffamine M-1000 acrylamide (to control gel swelling), and cysteamine-acrylamide bearing thiol groups. When mixed in aqueous solution with poly(ethylene glycol) diacrylate (PEGDA), the polymer system crosslinks by Michael-type addition, resulting in an elastic dual physical-chemical gel. Methods: Copolymers were synthesized and then characterized using NMR (composition), HPLC (molecular weight), and cloud point determination (LCST). The copolymer systems (copolymers + PEGDA) were characterized by rheometry, a gel swelling study, a catheter injectability test, and in glass aneurysm flow models. Results and Discussion: The polymers were synthesized with slightly lower JAAm content than feed. The polymers, 0, 10, and 20 % JAAm had LCST all between 28-33Â°C and Mn~10 kDa. Swelling increased with JAAm content. Greater JAAm inclusion showed faster decrease in phase angle after mixing with PEGDA, lower phase angles, and shear moduli which were less sensitive to frequency. All of these indicate that crosslinking is faster and more complete in gels containing JAAm. JAAm-containing polymers were injectable through a warm microcatheter for over 3 minutes while those without JAAm were not injectable after 30 seconds. Gels with JAAm, however, were too weak to remain in glass aneurysm models under high flow conditions (80 mL/sec) for more than 1 hr. Conclusions: A desirable LCST (below body temperature) was obtained for all polymers. JAAm content of 16 wt% provided gels that retain their volume adequately for embolization and are injectable for a longer time post-mixing. Gels with JAAm are initially weaker, but are highly elastic and of similar modulus after crosslinking. Higher molecular weight polymers of similar composition will be synthesized in future work to provide increased modulus while preserving the deliverability, swelling control, and elasticity observed in this class of materials.
6:00 AM - OO3.23
Colorimetric Detection of Microcystin-LR Using Peptide-derived Au Nanoparticles
Nicholas Bedford 1 Joe Slocik 1 Rajesh Naik 1
1Air Force Research Laboratory Wright-Patterson Air Force Base USAShow Abstract
The need for simple, specific detection of water-borne contaminates is an ever growing concern given the diverse chemical nature of water pollutants derived from various industrial, domestic and biologically sources. Microcystin-LR (MC-LR) is a cyanobacteria toxin commonly found in fresh water sources containing algae blooms which can produce MC-LR at dangerous concentrations. In this study, Au nanoparticles are created using fusion peptides containing sequences for Au ion precipitation and MC-LR binding. As MC-LR is introduced to the Au nanoparticle solution, the MC-LR binds in close proximity to the Au nanoparticles, causing a colorimetric change. Due to the specificity of the peptide for MC-LR, this colorimetric sensor only changes color in the presence of MC-LR and not in the presences of similar toxins.
6:00 AM - OO3.24
The Effects of CTAB on Single-stranded DNA Binding to Gold Nanorods
Richard Sullivan 1 Maeling N Tapp 1 Rajesh Naik 1 Valeria Milam 1 2
1Georgia Institute of Technology Atlanta USA2Georgia Institute of Technology Atlanta USAShow Abstract
Cetyltrimethylammonium bromide (CTAB) surfactant is commonly used to mediate the growth of gold nanorods (AuNRs) from spherical gold nanoparticle seeds. We have synthesized uniform AuNRs with an aspect ratio of 3 to 4 using a seeded growth method. While the presence of CTAB appears crucial to the anisotropic growth of AuNR from spherical seeds, UV-Vis and FTIR spectroscopy studies indicate that CTAB is only weakly bound to the AuNR surface. As CTAB is removed through multiple washing steps, the AuNRs visibly aggregate. Interestingly, aggregated AuNR suspensions were at least partially restabilized if CTAB was reintroduced to the suspension. Here, we explore the effects of adding a random library of 69 base long single-stranded DNA sequences to the growth solution in both the presence and absence of CTAB to study the effects of biological macromolecules on the size and shape of resulting gold nanoparticles. The resulting gold nanoparticles were characterized using spectroscopy as well as TEM and dynamic light scattering.
6:00 AM - OO3.25
Multifunctional Antioxidant Rare Earth Nanoparticles: Targeting, Delivery and Protection of Neuronal Cells in Alzheimer Model
Amit Kumar 1 2 3 Soumen Das 1 2 3 Annamaria Cimini 4 Barbara D'Angelo 4 Elisabetta Benedetti 4 Virendra Singh 1 Antonina Monaco 5 Sandro Santucci 5 Sudipta Seal 1 2 3
1University of Central Florida Orlando USA2University of Central Florida Orlando USA3University of Central Florida Orlando USA4University of L'Aquila L'Aquila Italy5University of L'Aquila L'Aquila ItalyShow Abstract
Oxidative stress and Î²-amyloid are considered as major pathological factors in the Alzheimer disease. Therefore, selected delivery of drug and/or antioxidant to the affected area (Î²-amyloid plaque) may stop the disease progression. Antibody conjugated nanoparticles have been researched for detection, identification, imaging and targeting. However, there is always a concern of proper antibody orientation, restricted interaction due to the steric hindrance and fast clearance from the biological system. Herein we report a systematic design of nanoparticle conjugated with antibody for selected targeting. For this purpose Anti-Î²-amyloid antibody was conjugated with oxide nanoparticle (cerium oxide nanoparticles; CNPs), which is a novel regenerative antioxidant nanoparticles, for targeting plaque in an in-vitro Alzheimer model. To reduce the steric hindrance between the antibody and targeted ligand, poly-ethylene glycol (PEG) spacer of 18.1Ã. was used. First â?"NH2 functionalized nanoparticle were synthesized and PEG were attached. Single force microscopy was used to confirm the stealth effect of PEG coated CNPs. Surface charge of nanoparticle coated with PEG was used to properly orient the antibody and then conjugated using EDC/Sulfo-NHS chemistry. Enhanced targeting and increased bio-compatibility were observed in case of CNP-PEG-Ab as compared to CNP-Ab. Moreover, preservation of neural structure was observed by modulating the BDNF signaling pathway in in-vitro Alzheimer model using this novel Ab conjugated antioxidant nanoparticle.
6:00 AM - OO3.26
Colorimetric Protein Detection: Plasmonic Shift via DNA-Au Nanoparticle Flocculation based on Chemically Engineered DNA-M13 Bacteriophage Platform
Ju Hun Lee 1 Jennifer Cha 1
1University of California, San Diego La Jolla USAShow Abstract
For early-stage disease diagnosis, advanced biomarker detection systems are highly critical. In addition, the sensors need to be convenient to run, reliable and low-cost to have global applicability. Previously, we demonstrated a biosensor system based on chemically modified thiolated M-13 bacteriophage that could induce rapid color changes after mixing with metal nanocrystals due to the plasmon shifts in direct response to antigens in solution. Some of the major benefits of using M13 bacteriophage platforms were that these bioscaffolds are easy to replicate, are stable in most environments as compared to enzymes, have the inherent ability to recognize other biomolecules and possesses over 2700 major coat proteins which can serve as modes to generate amplified signals. In most diseases including cancer however, multiplexed detection of various proteins is needed. To meet this challenge, we demonstrate here our recent efforts on using DNA modified bacteriophage to generate amplified colorimetric changes in solution. We modified the major capsid protein of M13 bacteriophage with DNA using amine-succinimidyl ester and thiol-maleimide chemistry. The DNA conjugated phage were reacted with various antigens in solution and captured magnetically using iron oxide beads. The bound DNA-M13 bacteriophage were then released into solution by chemical denaturation and then detected by adding DNA-conjugated metal nanocrystals to generate colorimetric changes in solution. These strategies are being explored for multiplexed protein detection in solution by reading the specific DNA conjugated to the nanoparticles or to the phage.
6:00 AM - OO3.27
Peptidomimetic Element for Controlling Polymer Brush Grafting Density, Protein Adsorption and Cell Attachment
K. H. Aaron Lau 1 2 Jinghao Kuang 1 2 Kevin P Anderson 1 Phillip B Messersmith 1 2
1Northwestern University Evanston USA2Northwestern University Evanston USAShow Abstract
Efficient control of the surface density of biofunctional molecules is non-trivial. Strategies developed for one substrate or biomolecule often prove to be ineffective with other materials due to subtle changes in substrate chemistry. The surface concentrations of co-deposited molecules often do not match the ratio in the source material. We previously introduced a mussel adhesive-inspired oligopeptide for surface grafting of antifouling polypeptoid brushes. We now demonstrate the versatility of this peptidomimetic element for controlling the surface grafting density of different polymer brushes with a range of chain lengths. Both electrostatically neutral species and those with charged sidechains are investigated. Colloid probe AFM is used to characterize the pH, ionic strength and surface density responses of the charged polymer brushes. We show how the ability to control the surface chain density enables the control of adsorbed protein density, and the relationship between protein density and cell attachment is investigated.
6:00 AM - OO3.28
Immobilization of Nanoparticles onto Carbon Nanotubes Based on Affinity Binding Peptides
Yuichiro Shimada 1 2 Mitsuo Umetsu 2 3 Takuma Chikamoto 2 4 Mizuaki Suzuki 4 Masakazu Sugiyama 2 5 Hiroyuki Fujita 1 2
1The University of Tokyo Tokyo Japan2BEANS Project Tokyo Japan3Tohoku University Sendai Japan4Seiko Instruments Inc. Tokyo Japan5The University of Tokyo Tokyo JapanShow Abstract
Carbon nanotube (CNT) is an attractive material possessing unique electrical and mechanical properties. Such properties of CNTs hold great promise for development of nano-electronic devices, such as FET, flexible electrode and electrical wiring. Especially, functionalization of the CNT surface by nanomaterials and enzymes is a key technique for the construction of a photoelectric conversion element and a high-sensitivity sensing device. Meanwhile, peptides with specific molecule recognition have a potential for the immobilization of nanomaterials on solid surfaces without special treatments or complicated processes. The functionalization process using peptides with specificity will open a way to high-valued CNTs device with nanomaterials. In this study, we screened the CNT binding peptides (CNTBPs) from peptide-displayed phage library system, and demonstrated the direct arrangement of CdSe nanoparticles onto the surface of CNTs using CNTBPs. We newly identified peptides with an affinity for single-walled (SW) or multi-walled CNT, corresponding to CNPBP1 [HMSHKQTRLSSG] or CNTBP2 [HMGLTKIHYSAL], respectively. The CNTBPs were chemically synthesized with a biotin molecule on Lysine residue at C-terminus via a glycine linker (CNTBP-[GGGSK]-biotin). To investigate the ability of the peptides for immobilization of nanomaterials onto CNT surface, we applied streptavidin-conjugated CdSe nanoparticles as a model compound, which possessed fluorescence, and introduced CNTBPs onto the CdSe surface via avidin-biotin bonding. The nanoparticles with CNTBPs were mixed to the CNT suspension in the buffer solution at room temperature. After removing unbound particles, the fluorescence from CdSe was detected on the suspension only in the case with CNTBP; in contrast, no luminescence was observed in the case without the peptide. Through TEM and SEM observation of the suspension, we found CdSe nanoparticles were bound and arrayed onto the CNT surface, and confirmed that the both of CNTBP1 and CNTBP2 could be used to functionalize SWCNT. Furthermore, we applied the peptide-assisted immobilization method to the bridge of SWCNTs between the tapered electrodes on Si, which was obtained through dielectrophoresis of CNTs. The device chip was soaked in the buffer containing CNTBP2 and CdSe nanoparticles, and then it was washed with ultrapure water and dried up by N2. In fluorescence microscope observation, the emission from CdSe was detected only in the position of CNTs, while no emission was found on either Al electrode or Si substrate. As evidenced here, the CNTBP has highly-selective binding capability against CNTs, and this simple one-pod-mixing process for the selective surface functionalization of CNTs has a widespread potential for the fabrication of high-sensitivity and high-selectivity sensors using CNT-based nanostructures.
6:00 AM - OO3.29
Electrostatically Driven Bio-Inspired Hierarchical Artificial Vascular Networks
Kristopher D. Behler 1 Zachary R Melrose 1 Andrew Schott 1 Eric D Wetzel 1
1U.S. Army Research Laboratory Aberdeen Proving Grounds USAShow Abstract
Vascular networks provide a method to distribute fluid throughout a system. Artificial vascular materials with enhanced properties are being developed that could ultimately be integrated into systems reliant upon fluid transport while retaining their structural properties. An uninterrupted and controllable supply of liquid is optimal for many applications such as continual self-healing materials, in-situ delivery of optically index matched fluids, thermal management and drug delivery systems could benefit from a bio-inspired approach that combines complex network geometries with minimal processing parameters. Two such approaches are electrohydrodynamic viscous fingering (EHVF) and electrical treeing (ET), both harnessing an electrostatic approach to network growth. Viscous fingering (VF) is a phenomenon that occurs when a low viscosity liquid is forced through a high viscosity fluid or matrix. The flowing liquid will branch, or form fingers due to capillary and viscous forces. EHVF is a modification on viscous fingering in which a DC voltage (10-60 kV) is applied to the low viscosity conductive fluid and forced through a dielectric matrix material, inducing fingers with a reduction in size and an increased branching behavior. The ensuing patterns mimic those found in biology and geology. Observation of VF and EHVF requires Hele-Shaw conditions in which a 2D system must possess a thin gap or in a porous 3D system. In the 2D instance silicone oil or PDMS was used. The interfacial tension was reduced by optimizing the surfactant concentration, resulting in branched pattern of small diameter fingers. Various filler materials were used to represent a more 3D system. Matrix filling reduces finger relaxation and allows for curing. Interfacial polymerization was also investigated. Robust, polymerized, fingers were formed and subsequently filled showing fluid transport. In moving more toward a true 3D system, materials such as fumed silica and crushed glass were investigated under. ET is the result of partial discharges in a dielectric material. In the vicinity of a small diameter electrode, the local electric field is greater than the global dielectric strength, causing a local, step-wise, breakdown to occur forming a highly branched interconnected structure. ET growth is influenced by the geometric configuration of the electrodes. ET is a viable method to produce networks on a smaller, micron, scale than EHVF. Surface modified electrodes, by carbon nanotube deposition, aid in increasing the local field, enabling a higher rate of tree initiation and growth. Inclusion of particles was investigated to determine if the growth direction can be manipulated. The use of self-clearing electrodes was investigated by UV dye infiltration through the hollow channels. Fluid delivery can be tailored through the applications of different electrode and ground manufacturing techniques for optimized flow rates for a given application.
6:00 AM - OO3.3
Peptide-based Synthesis, Characterization and Catalytic Applications of Metal Nanoparticle Networks
Rohit Bhandari 1 Marc R Knecht 1
1University of Miami Coral Gables USAShow Abstract
Recent advances in the development of methods for the fabrication of metallic nanostructures reveal great interest in adapting bio-inspired approaches to achieve technologically important materials. By employing such processes, emerging directions could be achieved for the production of inorganic materials under eco-friendly conditions of solvent, temperature, and pressure; however, new methods to control the shape, size, and composition are required. Among these materials, Pd nanoparticles attract great attention due to their excellent catalytic properties. We have fabricated multiple inorganic nanomaterials using a self-assembling peptide that acts as a template in the solution where spherical as well as non-spherical nanostructures can be prepared. Spherical particles, 1-dimensional nanoribbons, and dense/networked nanoparticle networks (NPNs) were observed by selecting the metal:peptide ratio in the reaction. The synthetic method and final nanostructures were fully characterized by UV-vis spectroscopy, transmission electron microscopy, dynamic light scattering, and powder X-ray diffraction analysis. The synthesized nanostructures were subsequently employed as catalysts for two entirely different classes of reactions, including Stille coupling and 4-nitrophenol reduction, such that the catalytic efficiency of the materials was studied as a function of both the inorganic composition and structure and the peptide template in solution. Catalytic loading and turnover frequency analyses demonstrated that these two characteristics worked in combination to control the reactivity of the materials. From this analysis, the spherical nanoparticles and NPNs demonstrated higher reactivity as compared to the 1-dimensional nanoribbons for all of the selected catalytic reactions. This unique reactivity trend is likely to be dependent upon two factors: the metallic surface area and the reagent penetration depth within the peptide scaffold. Such results could prove to be critical for future research for the fabrication of nanocatalysts where the composite/stabilizing structure mediates the reactivity of the materials. Also, these materials provide a green and effective route for catalyzing C-C coupling as well as direct surface reactions with high efficiency, complying with energy demands that are likely to be highly important for the future generation energy-efficient catalysis.
6:00 AM - OO3.5
Crystallographic Recognition Controls Peptide Binding and Activity for Bio-based Nanomaterials
Ryan H Coppage 1 Joseph M Slocik 2 Beverly D Briggs 1 Anatoly I Frenkel 3 Hendrik Heinz 4 Rajesh R Naik 2 Marc R Knecht 1
1University of Miami Coral Gables USA2Air Force Research Labs Wright-Patterson Air Force Base USA3Yeshiva University New York USA4University of Akron Akron USAShow Abstract
Peptides have been isolated with the ability to specifically bind inorganic materials to generate nanoparticle-based systems; however, the binding mechanism by which these peptides recognize and bind with the nanostructures at high affinity is still relatively unknown. By understanding this level of chemical interactions, nanoparticles could be designed that optimize both size and surface availability for a variety of applications ranging from catalysis to biomedical sensing. Furthermore, such systems are envisioned to operate under environmentally friendly and energy efficient conditions and may address issues related to future energy concerns. To probe this effect, we have isolated the Pd4 peptide, which is able to generate nearly monodisperse Pd nanocatalysts and have begun to explore its specific surface binding effects. To explore this phenomenon, we have selectively altered the binding capability through histidine residue substitutions in the peptide sequence. Catalytic analysis of the generated nanoparticles demonstrated a direct correlation between the reactivity and the peptide sequence, which suggests that the biotic/abiotic interface plays a critical role in the overall materialâ?Ts functionality. Furthermore, by modifying the Pd:peptide ratio employed during materials synthesis, we have observed size control via the actual peptide sequence, which is in direct contrast with typical ligand-based nanoparticle preparation routes. Together, this suggests that peptides can recognize the crystalstructure of the material and bind once such inorganic structural features are present in the reaction mixture. These results are significant as they begin to demonstrate mechanistic understandings of these biologically influence interactions, which could lead to progress toward the ability to design highly specific biotic-abiotic interfaces at the atomic level with structural control of complex inorganic materials that could be immediately employed in a vast array of technologically important applications.
6:00 AM - OO3.6
Nano-pipette Directed Motion of Biomimetic Transmembrane Channel
Meenakshi Dutt 1 Olga Kuksenok 2 Anna C Balazs 2
1Rutgers University Piscataway USA2University of Pittsburgh Pittsburgh USAShow Abstract
Via Dissipative Particle Dynamics (DPD) approach, we study the directed motion of a transmembrane end-functionalized nanotube using a suitably functionalized nano-pipette. In our earlier work (Nanoscale 2011), we demonstrated the design and creation of biomaterials which promote controlled release by integrating end-functionalized nanotubes into lipid bilayers. Each nanotube encompasses an ABA architecture, with a hydrophobic shaft (B) and two hydrophilic ends (A). To allow controlled transport through the nanotube, we also introduce hydrophilic tethers at one end of the tube. We showed that nanotubes initially located in the outer solvent spontaneously penetrate the membrane and assume a trans-membrane position, with the hydrophilic tethers extending from the surface of the bilayer. The hydrophilic tethers can also serve as anchors for directing the motion of the inserted nanotube across the membrane. We demonstrate this process by locating a suitably functionalized nano-pipette near such an end-functionalized nanotube. The nanotube diffuses in the membrane until the tethers are close to the nano-pipette. Due to favorable interactions, the tethers anchor onto the nano-pipette. We also show that the nanotube motion can be controlled through the nano-pipette.
6:00 AM - OO3.7
Probing the Limits of Aptamer Affinity with a Microfluidic SELEX Platform
Kareem Marcel Ahmad 1 Seung Soo Oh 2 Seon Kim 3 Forrest M McClellen 4 Yi Xiao 2 5 H. Tom Soh 1 2 5
1University of California, Santa Barbara Santa Barbara USA2University of California, Santa Barbara Santa Barbara USA3University of California, Santa Barbara Santa Barbara USA4University of California, Santa Barbara Santa Barbara USA5University of California, Santa Barbara Santa Barbara USAShow Abstract
Nucleic acid-based aptamers offer many potential advantages relative to antibodies and other protein-based affinity reagents, including facile chemical synthesis, reversible folding, improved thermal stability and lower cost. However, their selection requires significant time and resources and selections often fail to yield molecules with affinities sufficient for molecular diagnostics or therapeutics. Towards a selection technique that can efficiently and reproducibly generate high performance aptamers, we developed a microfluidic selection process (M-SELEX) that can be used to obtain high affinity aptamers against diverse protein targets. Here, we isolated DNA aptamers against three protein targets with different isoelectric points (pI) using a common protocol. After only three rounds of selection, we discovered novel aptamer sequences that bind to platelet derived growth factor B (PDGF-BB; pI = 9.3) and thrombin (pI = 8.3) with respective dissociation constants (Kd) of 0.028 nM and 0.33 nM which are both superior to previously reported aptamers against these targets. In parallel, we discovered a new aptamer that binds to apolipoprotein E3 (ApoE; pI = 5.3) with a Kd of 3.1 nM. Furthermore, we observe that the net protein charge may exert influence on the affinity of the selected aptamers. To further explore this relationship, we performed selections against PDGF-BB under different pH conditions using the same selection protocol, and report an inverse correlation between protein charge and aptamer Kd.
6:00 AM - OO3.8
Collisional Quenching-based Fluorescence Glucose Sensing Using Enzyme-immobilized ZnO Nanocrystals
Ki-Eun Kim 1 Yun-Mo Sung 1
1Korea University Seoul Republic of KoreaShow Abstract
As an alternative to electrochemical sensing, many researchers are exploring fluorescent methods for biological sensing. Fluorescence sensing relies on the interaction between fluorophores and analytes that causes the change in the optical signals of fluorophores. The use of fluorescent indicators can provide sensitive and selective detection in liquid media which has led to widespread use in biological analysis. Currently, organic fluorophores have been replaced with inorganic semiconductor and metal nanoparticles, especially quantum dots, because of their high resistance to photo-bleaching and intense light emission by high quantum efficiency. Also, tuning the color of light emission can be achieved simply by changing the particle size due to quantum confinement effect. However, fluorescent glucose biosensors based on quantum dots are highly limited. In this study a simple approach to sensitive glucose detection has been developed based upon variation in the fluorescence of ZnO nanocrystals with glucose concentration. ZnO nanocrystals were successfully synthesized in wurtzite structure using a surfactant, mercaptoundecanoic acid (MUA) via the polyol method. MUA molecules not only served as a template for the synthesis of spherical-shape nanoparticles but also provided water solubility and biocompatibility due to its carboxyl group. Carboxyl-terminated ZnO nanocrystals were activated by esterification of n-hydroxysulfo-succinimide (Sulfo-NHS) catalyzed by water-soluble 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). Glucose oxidase (GOx), an enzyme could be immobilized to ZnO nanocrystals by replacing NHS with amino-acid groups of GOx. ZnO-MUA-GOx bioconjugates showed decrease in the photoluminescence (PL) intensity by appearance of glucose molecules due to the collisional quenching by hydrogen peroxide generated from enzymatic oxidation reaction of glucose. PL intensity showed linear decrease with glucose concentration from 1.6 to 33.3 mM, which fully covers physiological glucose level. ZnO-MUA-GOx bioconjugates showed detection limit lower than 0.33 mM and response time less than 5 sec. They also revealed distinct specificity against cholesterol molecules.
6:00 AM - OO3.9
Combination Self-assembly of beta;-sheet Peptides and CNT: Functionalizing CNT with Bioactive beta;-sheet Block Copolypeptides
Woo-Jin Jeong 1 Yong-beom Lim 1
1Yonsei University Seoul Republic of KoreaShow Abstract
Carbon nanotubes are intrinsically insoluble in aqueous solution. Since biological systems are composed of water-soluble structures, the solubilization of CNTs in aqueous solution is a prerequisite for their use in bioapplications. In addition, surface functionalization of CNTs with biologically active molecules is important to give them specific biological functions. The two main approaches for the solubilization of CNTs are based on covalent and noncovalent functionalization. In covalent functionalization, functional groups such as carboxylic acids or amines are formed by chemical reactions in defect sites of CNTs, which can then be used as sites for conjugation reactions with bioactive molecules. The problem with this approach is that it can damage the intrinsic structural and electrical properties of pristine CNTs. By contrast, the noncovalent approach can potentially preserve the Ï?-conjugated system of CNTs. This approach usually uses amphiphilic molecules, in which the hydrophobic part of the molecule wraps around the wall of CNTs, and the hydrophilic part interacts with an aqueous solution. Various types of molecules including low molecular weight amphiphiles or surfactants, polymers, carbohydrates, DNAs or RNAs, proteins, and peptides, have been used to noncovalently functionalize and solubilize CNTs. Peptides(the minimal form of proteins) can be developed as protein-like artificial nanomaterials when properly designed and self-assembled into controllable and elaborate nanostructures. It has recently been demonstrated that self-assembled peptide nanostructures based on Î²-sheet peptides can be developed as promising biomaterials. Notably, self-assembling Î²-sheet peptides can be functionalized to become bioactive nanostructures when a biologically active and hydrophilic peptide segment is conjugated to the Î²-sheet segment, yielding bioactive Î²-sheet block copolypeptides. In doing so, diverse types of controlled and biologically useful Î²-sheet peptide nanostructures could be fabricated. Herein, we present systematic investigation of the combination self-assembly between the bioactive Î²-sheet block copolypeptides and CNTs. This type of self-assembly system includes force balance processes between two classes of completing forces: the attractive forces between Î²-sheet segments, and the attractive forces between Î²-sheet segments and CNTs. If the former predominates, the peptides construct Î²-sheet nanostructures while CNTs are still insoluble. On the other hand, water-soluble CNTs noncovalently functionalized with the bioactive Î²-sheet block copolypeptides can be constructed if the latter becomes dominant. This research is important in fabricating peptide-decorated bioactive and functional CNTs. Moreover, understanding such force balance processes is valuable for controlling and thereby inhibiting aggregation behavior of Î²-amyloids and related proteins in protein misfolding diseases.
OO1: Bio-enabled Material Templates
Tuesday AM, April 10, 2012
Marriott, Yerba Buena, Nob Hill BC
9:30 AM - *OO1.1
From Atoms to Structures -How Spiders turn Weakness into Strength
Markus J Buehler 1
1MIT Cambridge USAShow Abstract
This talk will explain how materials in biology are synthesized, controlled and used for a variety of purposesâ?"structural support, force generation, catalysis, or energy conversionâ?"despite severe limitations in available energy, quality and quantity of building blocks. We demonstrated that the chemical composition of biology's materials plays a minor role in achieving functional properties. Rather, the way components are connected at different length-scales defines what material properties can be achieved, how they can be altered to meet functional requirements, and how they fail in disease states. We have achieved this by using the worldâ?Ts fastest supercomputers to predict properties of complex materials from first principles, in a multiscale approach that spans orders of magnitude in scale. This method, combined with experimental studies, allows us to build virtual â?oin silicoâ? material models that provide unseen insight into the workings of natural and synthetic materials from the bottom up. We demonstrate this approach in a case study of spider silk, one of the strongest yet most flexible materials in Nature, despite being made out of some the simplest, most abundant and intrinsically weak proteins, including weak hydrogen bonding. We discovered that the great strength and flexibility of spider silkâ?"exceeding that of steel and other engineered materialsâ?"can be explained by the materialâ?Ts unique structural makeup that involves multiple hierarchical levels. These hierarchical levels span from the genetic information that defines the protein sequence to the structural scale of an entire spider web. Thereby, each level contributes to the overall properties, but the remarkable properties emerge because of the synergistic interaction across the scales where the sum is more than its parts. By translating this insight gained from the study of natural materials such as spider silk to engineered materials such as carbon nanotube fibers, graphene composites or metal-polymer films, our research has resulted in an engineering paradigm that facilitates the design of sustainable materials starting from the molecular level, leading to the formation of hierarchical structures that span all scales from nano to macro. By utilizing a mathematical tool from category theory we illustrate the hierarchical materials design concept by drawing an analogy to a seemingly far and distant fieldâ?"music. Reminiscent of protein materials, the integrated use of structures at multiple scales is the key to provide superior functional properties despite limitations in available building blocks, a set of musical instruments such as piano, violin or cello. In music, tones are played at different pitch, accentuation or duration and then assembled into melodies. The collective interaction of melodies, played by different instruments and arranged in a particular way, eventually results in the powerful expression of a symphony.
10:00 AM - OO1.2
Robust and Responsive Silk Ionomer Microcapsules
Chunhong Ye 1 2 Olga Shchepelina 2 Irina Drachuk 2 Rossella Calabrese 3 David L Kaplan 3 Vladimir V Tsukruk 2
1Nanjing Forestry University Nanjing China2Georgia Institute of Technology Atlanta USA3Tufts University Medford USAShow Abstract
We demonstrated the LbL assembly of thin shell microcapsules from biocompatible and biodegradable silk fibroin counterparts modified with poly(lysine) and poly(glutamic) acid. Grainy, porous texture and exponential growth shell facilitate their high permeability. The crosslinked microcapsules are robust and extremely stable in the unusually wide pH range from 1.5 to 12.0 in striking contract to conventional synthetic polyelectrolyte LbL capsules which are readily dissolved at extreme pH conditions. These microcapsules show pH triggered response at acid (pH < 2.5) and basic (pH > 11.0) conditions with 800% increases in volume without compromising capsule integrity. These changes are accompanied by reversible changes in â?oopen/closedâ? shell morphology which are exploited for pH-triggered loading and unloading of large macromolecules.
10:15 AM - OO1.3
Protein Nanofibers as Functional Templates in Hybrid Bionanomaterials
Christoph Meier 1
1Ulm University Ulm GermanyShow Abstract
Peptides and proteins are able to undergo specific self-assembling pathways resulting in the formation of nanofibers with diameters in the range of a few nanometers and lengths exceeding several micrometers. In addition to their implications in neurodegenerative diseases such as Alzheimer's and Parkinson's, an important aspect of such so-called amyloid fibers is their role as functional entities in biological systems. They adopt important roles in biosynthetic pathways and as structural components in lower organisms. The highly ordered arrangement of the peptide chains within the nanofibers, the high nanofiber aspect ratio and the presence of a large variety of functional groups makes them interesting building blocks and templates for novel biological nanomaterials. However, the ability to exploit the functional properties of natural protein nanofibers and to transfer their nanoscopic properties into macroscopic materials are key issues on their way towards nanotechnological applications. Herein, we discuss how the chemical and physical properties of amyloid nanofibers can be exploited to develop polymeric and inorganic peptide hybrid nanomaterials. Using noncovalent interactions, amyloid nanofibers can be spun into high-performance biofibers with diameters from tens to hundreds of Âµm, exhibiting tensile strengths of about 300 MPa and elastic moduli of about 10 GPa. Within the macroscopic material, the nanofiber building blocks adopt a highly ordered arrangement and template the mineralization of calcium phosphate. The resulting hierarchically structured biocomposite exhibits a significant increase in bending rigidity and mimicks the structural characteristics of fibrolamellar bone. In addition, protein nanofibers are known to exhibit hydrophobic binding pockets that are able to interact with small organic molecules, e.g dyes. Here, we demonstrate that the nanofibers are capable to template the polymerization of small organic molecules into polymers, resulting in water-soluble nanoscopic 1D polymer-protein architectures. These novel polymer-protein hybrid nanomaterials have potential applications ranging from nanomedicin to energy conversion.  T. P. J. Knowles, A. W. Fitzpatrick, S. Meehan, H. R. Mott, M. Vendruscolo, C. M. Dobson, M.E. Welland. Science 2007, 318, 1900  D. M. Fowler, A. V. Koulov, W. E. Balch, J. W. Kelly. Trends Biochem. Sci. 2007, 32, 217  C. Meier, M. E. Welland. Biomacromolecules 2011, 12, 3453
10:30 AM - OO1.4
Infrared Transmission through Subwavelength Pores in Gold Replicas of Coscinodiscus Asteromphalus Diatoms
Yunnan Fang 2 Vincent W Chen 1 Ye Cai 2 John D Berrigan 2 Seth R Marder 1 Kenneth H Sandhage 2 Joseph W Perry 1
1Georgia Institute of Technology Atlanta USA2Georgia Institute of Technolgy Atlanta USAShow Abstract
Nature provides a vast number of intricate three-dimensional (3D) inorganic structures formed by living organisms. Diatoms (single-celled algae) are among the most versatile structure-forming organisms that form a silica-bearing microshell (frustule) with a specific 3D morphology in a rich variety of shapes and patterned features. Culturing of a given diatom species, followed by shape-preserving chemical conversion of the resulting frustules, can yield enormous numbers of structures with a particular 3D morphology, tailored chemistry, and potentially new (non-biological) properties. Coscinodiscus asteromphalus (CA) diatom frustules possess organized, quasi-periodic patterns of many hundreds of micrometer size pore diameters. Here we report the conversion of CA diatom frustules into 3D gold replicas via a scalable wet chemical process and the infrared transmission and reflection spectra of the gold replicas, which exhibit significant infrared transmission at wavelengths substantially larger than the diameters of the pores. The transmission spectra were simulated using a surface plasmon-interference model, which considers the excitation and interference of surface plasmons on the incident and exiting sides of the gold frustule replica, and radiation of optical energy from the exiting side. We will discuss the experimental and modelling results on the infrared properties of the gold CA replicas, as well as those of well-ordered hexagonal hole arrays and hole arrays matching the hole pattern of the CA frustules that were fabricated in gold films by focused ion beam milling. The reasonably good agreement between the simulated and measured position and intensity of the IR transmission peak indicate that the IR transmission of these gold frustule replicas was enabled by the generation, transmission, and radiation of surface plasmons.
11:30 AM - *OO1.6
Role of 3D Scaffold Structure in Controlling Stem Cell Shape and Differentiation
Carl Simon 1
1NIST Gaithersburg USAShow Abstract
It is well-known that 2D surface topography from the micro- to the nanoscale can influence stem cell behavior. However, the role of 3D scaffold structure in directing stem cell function has not been elucidated. Thus, we have used a library approach to systematically screen the effect of widely varied scaffold structures on primary human bone marrow stromal cell (hBMSCs) function. Microarray testing revealed that each type of scaffold structure tested induced a unique gene expression signature demonstrating that cells are keenly sensitive to scaffold structure. Further, hBMSC behavior was dependent upon scaffold structure. hBMSCs underwent osteogenic differentiation on nanofiber scaffolds while freeform fabricated scaffolds enhanced hBMSC proliferation. Since cell morphology and cell behavior are linked, hBMSC shape was assessed. hBMSCs took on a highly branched, elongated morphology on nanofiber scaffolds but had a well-spread, more rounded morphology on freeform fabricated scaffolds. These results suggest that scaffolds controlled hBMSC behavior by controlling their shape and indicate that 3D scaffold structure must be designed to drive cells into morphologies that direct their fate. Next, scaffold niche dimensionality was measured. Though it is widely accepted that 3D scaffolds present a more physiological environment than 2D substrates, it not known which scaffolds provide cells with a truly 3D niche. Thus, 3D confocal images of hBMSCs cultured in different scaffolds were analyzed to determine cell dimensionality. This required development of new imaging metrics to determine if cells had a predominantly 2D or 3D morphology. hBMSCs on flat surfaces were assessed as 2D controls. hBMSCs cultured in 3D scaffolds were not as â?o3Dâ? as was expected, but were more 3D than were hBMSCs cultured on 2D flat surfaces. Cells had differing degrees of 3Dness in the different scaffolds indicating that cell niche dimensionality varied with scaffold structure. This work yields a new approach for determining if a scaffold provides a 3D niche for cells. Taken together, these results provide a new way to think about how scaffold properties can be tuned to control stem cell fates through control of cell shape and dimensionality.
12:00 PM - OO1.7
Enzyme-guided Crystal Growth for Next Generation Biosensors
Roberto de la Rica 1 Laura Rodriguez-Lorenzo 2 Ramon Alvarez-Puebla 2 Luis M Liz-Marzan 2 Molly M Stevens 1
1Imperial College London London United Kingdom2Universidade de Vigo Vigo SpainShow Abstract
Enzymes are essential components of the bionanotechnology toolbox that have found applications in areas as relevant as nanomaterials synthesis, nanolithography and the fabrication of sensors.[3,4] In particular, enzymes have been shown to work as nanoreactors that finely control the kinetics of crystal growth to yield nanocrystals of defined size, shape and crystallinity. Furthermore, enzymes are extremely useful labels that amplify the signal of biosensors, a feature that has been extensively used in enzyme-linked immunoassays (ELISA). Here we present a new generation of biosensors that merge these two concepts to yield ultrasensitive sensors with characteristics that overcome some limitations observed in classical detection schemes. When combined with the specific recognition feature of antibodies, the proposed signal amplification method can be used as a universal platform to detect molecules of great medical relevance such as cancer biomarkers and infectious diseases. For example, we designed a signal amplification scheme that yields a larger signal when the target molecule is less concentrated, which allows the detection of ultralow concentrations of cancer biomarkers in serum with high confidence. In this approach, the optical properties of plasmonic transducers are tailored by the growth of silver nanocrystals guided by glucose oxidase. By harnessing the kinetics of crystal growth with the enzyme to control the morphology of the nanocrystals, the response of the sensor can be engineered to yield a drastic signal at ultralow concentrations of the analyte, which radically decreases the possibility of a false positive by undesired interferences. This is demonstrated by detecting the cancer biomarker prostate specific antigen (PSA) with a concentration as low as 1 ag/mL spiked into whole human serum. In another approach, the growth of gold nanoparticles is utilized as the signal in ELISA. The key step in this methodology is to limit the rate of growth of the nanocrystals with the enzyme catalase so that the intensity of the color of the solution depends on the concentration of target molecule. Moreover, the enzyme also determines the size and morphology of the nanocrystals, which dictates a change in the color of the solution from blue to red that allows detecting ultralow concentrations of clinically relevant proteins by simple visual inspection. The signal amplification mechanism based on enzyme-guided crystal growth could be adapted to other optically active nanocrystals such as quantum dots.  de la Rica, R.; Matsui, H. Angew. Chem. Int. Ed. 2007, 47, 5415-5417.  de la Rica, R.; Fabijanic. K. I.; Baldi, A.; Matsui, H. Angew. Chem. Int. Ed. 2010, 49, 1447-1450.  de la Rica, R.; Fratila, R.; Szarpak, A.; Huskens, J.; Velders, A. H. Angew. Chem. Int. Ed. 2011, 50, 5703-5706.  Aili, D.; Mager, M.; Roche, D.; Stevens. M. M. Nano Lett. 2011, 11, 1401-1405.
12:15 PM - OO1.8
Spatially Modulated Doping of Single-layer Graphene and MoS2 by Self-assembled Peptide Nanowires
Yuhei Hayamizu 1 2 Christopher R So 1 Mehmet Sarikaya 1
1University of Washington Seattle USA2Japan Science and Technology Agency (JST) Tokyo JapanShow Abstract
Developing elegant hybrid systems between biological molecules and nanomaterials is key in creating novel bio-nanoelectronic devices, where versatile biomolecular functions are integrated with well-established electronics of nanomaterials. Single-layer graphene, MoS2, and other atomic single layers (ASLs), represent ideal nanomaterials to form such bio/nano systems due to their two-dimensional structure. Biomolecules self-assembling into ordered nanostructures on ASLs offer a novel bottom-up technology, where organized biomolecular architectures spatially govern the electronics of ASLs. Despite the enormous potential in bridging nano- and bio-worlds at the molecular scale, no work has yet realized a way to combine the self-assembled nanostructures of biomolecules to control electronic and/or optical properties of ASLs. Here, we demonstrate that engineered dodecapeptides self-assemble into two-dimensional supramolecular networks of â?opeptide nanowiresâ?, on the surface of two different ASLs: single-layer graphene and MoS2. Peptide nanowires have uniform dimensions, typically ~1-nm thick, ~12-nm wide, and micro-meters in length, and introduce electric charges into single-layer graphene and MoS2via biomolecular doping. Unique to peptide nanowires, we find that their abrupt boundaries create electronic junctions in graphene, which manifest themselves within the single-layer as a self-assembled electronic network. Furthermore, we demonstrate that designed peptides modify both conductivity and photoluminescence of single-layer MoS2. Supramolecular peptides show unique electronic interactions with ASLs. While the absence of peptide organization on surfaces results in random doping, ordered peptide nanowires predictably modify the conductivity of graphene. The coherent peptide conformation in nanowire architectures on ASLs potentially provides new foundations to study primary interactions at the bio/nano interface. Furthermore, peptides with different amino acid sequences can recognize different types of ASLs, verified by the demonstration of unique molecularly ordered patterns on single-layer graphene and MoS2, respectively. Controlling nano-electronics through biologically-coded self-assembled peptides is now possible, potentially opening new avenues in self-assembled nanodevices for future bioelectronics and biophotonics. Research supported by NSF-MRSEC, NIH-T32, NSF-BioMat and JST-PRESTO programs.
Symposium OrganizersValeria Tohver Milam, Georgia Institute of Technology
Harry Bermudez, University of Massachusetts, Amherst
Rajesh Naik, Air Force Research Laboratory
Marc Knecht, University of Miami
Symposium Support National Science Foundation
Royal Society of Chemistry
The Journal Nanoscale
OO5: Structure-Function Design Strategies for Bio-enabled Materials Systems
Wednesday PM, April 11, 2012
Marriott, Yerba Buena, Nob Hill BC
2:30 AM - *OO5.1
Biomimetic 2D and 3D Superstructures from NPs/QDs, Collagen Peptides, and Catalytic Peptides Discovered through Evolution of Phage Display
Hiroshi Matsui 1
1City University of New York-Hunter College New York USAShow Abstract
The ability to control self-assembly of complex 2D and 3D architectures from functional building blocks could allow further development of complex device configurations. By mimicking natural systems, genetically engineered peptides with a variety of functional building blocks such as metal NPs can be applied to design new materials with the specificity of assembled structure, the robustness of assembly, and the versatility of the superstructure. Here, we present three types of large-scale (Âµm3 - mm3) biomimetic 2D and 3D assemblies using nanoscale collagen peptides as building blocks. The first example is to mimic bone tissues for the production of free-standing flexible collagen films. In this case, biotylated collagen peptides are assembled into films with streptavidin-functionalized QDs, which are used as molecular recognition-based cross-linking agents between biomolecular film domains to provide structural reinforcement and flexibility. The second example is to mimic S-layer proteins on bacteria and we assemble microcapsules from collagen peptides stable even in extreme pH or high temperature when the peptides are assembled on oil-in water droplets and the ends of peptides are capped/cross-linked by peptide-binding proteins. The third example is to assemble 3D reconfigurable superstructure crystals from collagen peptides in the large-scale with high yield. In this strategy, biotylated collagen peptides and ligand-functionalized nanoparticle hubs are self-assembled into 3D microcrystals in controlled structures and NP density with the precise nanoscale interparticle distance. This simple, rapid fabrication protocol produces high yields of 3D materials in controlled shapes, promising ease and flexibility in manufacturing future functional devices. The reconfigurability of the 3D directed assembly was also demonstrated by modifying peptides with genetic engineering. We discovered that the conformation change of peptide building blocks induced by pH could trigger the disassembly of the hybrid NP-peptide cube and undergo the reassembly into different shapes. We also develop peptides as building blocks of 3D superstructures that can also catalyze chemical reactions and metal growths at room temperature to develop further complex structures. This strategy is based on the combinatorial phage display library approach that can perform the novel panning process of peptides on the viruses growing the only target nanocrystal from the precursor solutions. To demonstrate the proof-of-concept, we examined to find catalytic peptides for room-temperature growth of ZnO nanocrystal by this approach. The combinatory phage display library identified the small number of peptide sequences for the ZnO growth and one of them, ZP-1 peptide, demonstrated the strong catalytic activity for the room temperature growth. We extended this approach to find catalytic peptides for various chemical reactions by catalytically forming/breaking targeted chemical bonds.
3:00 AM - OO5.2
Selection is More Intelligent than Design: Improving the Affinity of a Bivalent Aptamer through Directed Evolution
Kareem Marcel Ahmad 1 Yi Xiao 2 3 H. Tom Soh 2 3
1University of California, Santa Barbara Santa Barbara USA2University of California, Santa Barbara Santa Barbara USA3University of California, Santa Barbara Santa Barbara USAShow Abstract
Multivalent molecular interaction can be exploited to dramatically enhance the performance of an affinity reagent. Among many factors, the degree of enhancement in affinity and specificity achieved with a multivalent design critically depends on the effectiveness of the linker that joins the recognition ligands, as this determines their position and orientation with respect to the target molecule. The rational design of an optimal linker poses a serious challenge for targets with known structures, and remains an unsolved problem for the overwhelming number of targets whose structure and ligand binding sites are unknown. As an alternative to design-based strategies, we report here a selection-based method for generating optimal bivalent aptamers. For efficient selection, we utilized a microfluidic platform developed in our laboratory. Using thrombin as a model, we show that within five rounds of selection, we can generate bivalent aptamers with a dissociation constant (Kd) below ~10 pM: a ~1000-fold improvement over the monomeric aptamers and a ~10-fold improvement over the best rationally-designed constructs.
3:15 AM - OO5.3
Screening for DNA Aptamers that Bind to Gold Substrates
Maeling J. N. Tapp 1 Patrick B Dennis 2 Rajesh R Naik 2 Valeria T Milam 1
1GA Tech Atlanta USA2Air Force Research Laboratory Wright Patterson Air Force Base USAShow Abstract
Aptamers are single-stranded oligonucleotide sequences that exhibit high affinity and specificity binding for non-nucleotide targets. Using a process called "Systematic Evolution of Ligands by EXponential Enrichment" (SELEX), previous work has identified RNA and DNA aptamers for a variety of targets including but not limited to ions, small macromolecules, and whole cells. This work focuses on the use of SELEX to identify aptamer sequences that exhibit selective binding for gold substrates. First, we amplified our randomized single stranded DNA library using linear polymerase chain reaction. We then exposed the gold substrates to the ssDNA library, using stringent washing conditions to remove unbound or weakly bound sequences through a series of wash steps. The final steps involved recovery of strongly-bound sequences using a modified elution process comprised of temperature and buffer changes. Applying this approach, we have identified candidate aptamers that bind to gold substrates. This work aims to use oliognucleotide-mediated interactions to enable novel processing routes for complex architectures in nanomaterials.
3:30 AM - *OO5.4
Peptide-directed Cooperative Synthesis and Assembly of Nanoparticles: Methods, Structures, and Mechanistic Studies
Nathaniel L Rosi 1
1University of Pittsburgh Pittsburgh USAShow Abstract
A method for controlling the simultaneous synthesis and assembly of metallic nanoparticles will be presented. Particular focus will be given to how this method can be used to design new complex nanoparticle superstructues and tailor their structural metrics. In addition, particular focus will be given to new mechanistic insights into the simultaneous synthesis and assembly process.
4:30 AM - *OO5.5
Towards Evolvable Soft Matter
Rein V Ulijn 1
1University of Strathclyde Glasgow United KingdomShow Abstract
Self-assembly and catalysis are key properties of living systems. We are interested in exploiting these, in combination, to achieve control of supramolecular organization and consequent adaptive materials functionality. We have developed versatile gelator systems based on aromatic peptide amphiphiles, which self-assemble via a unique mechanism involving Ï?-interlocked Î²-sheets. These systems display highly tunable supramolecular functionalities, giving rise to materials with controlled mechanical properties, nanotopography and bioactive properties. We will demonstrate the use of catalysis to control and direct the self-assembly process towards various non-equilibrium states. These catalytic dynamic peptide libraries provide a first step towards evolvable nanomaterials. Finally, we will discuss progress the use of these gel matrices for controlled stem cell differentiation purely driven by supramolecular order.
5:00 AM - OO5.6
Amphiphilic Peptide-polymer Conjugates with Side-conjugation
Nikhil Dube 1 Andrew Presley 1 Jessica Shu 1 Ting Xu 1 2 3
1University of California, Berkeley Berkeley USA2University of California, Berkeley Berkeley USA3Lawrence Berkeley National Laboratory Berkeley USAShow Abstract
As an emerging family of soft matter, peptide-polymer conjugates are highly promising for the design of functional materials. The fundamental understanding of the effect of the interaction between peptides and polymers on the structural and functional properties of these materials is crucial for their development into technologically relevant materials. Incorporation of amphiphilicity in these hybrid materials could potentially impart novel self assembly properties and may enable the formation of hierarchically structured materials. We have been investigating the effect of site specific conjugation of polymers with different hydrophobicity on the secondary and tertiary structure of coiled coil helix-bundle peptides. Two hydrophobic polymers, polystyrene and poly(methylmethacrylate) were conjugated to the exterior of helix bundle. Conjugation of polystyrene results in unfolding of the helix and may induce Î±-helix to Î²-sheet conformational transition in the vicinity of the site of polymer conjugation, while poly(methylmethacrylate) disrupts the peptide structure to a lesser extent. However, the deleterious effects of hydrophobic polymers on the peptide structures can be eliminated on adding organic solvent to solubilize the hydrophobic polymers. In order to confirm the hypothesis of importance of the polymer hydrophobicity on peptide structure, conjugates of the peptide with a thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM), which exhibits a temperature controlled hydrophobicity, have been studied. The temperature dependence of the peptide structure underscores the significance of the hydrophobic interaction between the polymer and the peptide. These fundamental studies signify the importance of different competing interactions between peptide, polymer and solvent on peptide structure. In order to maintain the protein structures in peptide-polymer conjugates, the delicate balance between different intermolecular forces needs to be maintained. The future work involves the understanding of the effect of the molecular weight of the conjugated polymers on the peptide structure. Further investigations would also focus on the characterization of self assembly of polymer conjugates based on amphiphilic helix bundle peptides. These systematic studies are expected to provide useful guidelines for establishing design principles to maintain peptide structure and function in these hybrid materials.
5:15 AM - OO5.7
Template Engineering through Epitope Recognition: A Modular Design Strategy for Bio-enabled Inorganic Synthesis
Alia P Schoen 1 2 David T Schoen 1 Kelly N Huggins 1 2 Manickam Adhimoolam Arunagirinathan 1 2 Sarah C Heilshorn 1 2
1Stanford University Stanford USA2SLAC National Accelerator Laboratory Menlo Park USAShow Abstract
Natural systems often utilize a single protein to perform multiple functions. Control over functional specificity is achieved through interactions with other proteins at well-defined epitope binding sites to form a variety of functional co-assembled structures. Inspired by the biological use of epitope recognition to perform diverse yet specific functions, we present Template Engineering Through Epitope Recognition (TEThER), a strategy that takes advantage of noncovalent, molecular recognition between different components to achieve functional versatility from a single protein template. Engineered TEThER peptides are designed to serve as molecular bridges between protein epitope binding sites and the surrounding environment in a localized, specific, and versatile manner. The peptides discussed in this work are bifunctional sequences that span the biologic-inorganic interface by noncovalently binding to specific recognition sites on the protein scaffold and serving as sites for localized bio-enabled nucleation and growth of inorganic materials. Clathrin, a protein that plays a key role in the dynamic remodeling of the cell membrane during endocytosis, provides a framework that offers access to a variety of architectures outside of a cell, such as cages, barrels, tetrahedra, and cubes. This structural diversity makes clathrin an attractive candidate for use as a versatile protein scaffold. Formation of these architectures is achieved by modulating environmental conditions to induce self-assembly (pH, concentration, ionic strength). We have begun a systematic study of these environmental conditions to gain an understanding of the kinetic and thermodynamic principles of self-assembly and predictive, controllable structuring of clathrin. We functionalized self-assembled clathrin protein cages at specific sites through co-assembly with designer TEThER peptides to achieve three diverse functions: the bio-enabled synthesis of gold, cobalt oxide, and anatase titanium dioxide nanoparticles in aqueous solvents at room temperature and ambient pressure. Compared with previous demonstrations of site-specific bio-enabled inorganic synthesis, the TEThER strategy relies solely on defined, noncovalent interactions without requiring any genetic or chemical modifications to the protein template. Therefore, this design strategy represents a mix-and-match, biomimetic approach to achieve versatile and site-specific functionalization that can be broadly applied to other protein templates to generate structures with a range of functionalities.
5:30 AM - OO5.8
Dynamic Templating of Metal Nanoparticles via Biocatalytic Self-assembly
Sangita Roy 1 Rein V Ulijn 1
1University of Strathclyde Glasgow United KingdomShow Abstract
The combination of biocatalysis and molecular self-assembly underpins vital dynamic processes in biological systems involving molecular movement and transport. There is currently a significant interest in producing synthetic mimics of such biocatalytic supramolecular transformations for nanomaterials fabrication. We will demonstrate how biocatalytic self-assembly of an aromatic peptide amphiphile can be exploited as dynamic templates for formation of noble metal nanoparticles. We use the supramolecular hydrogel of Fmoc-FY, produced by enzymatic dephosphorylation for the synthesis of gold nanostructures under physiological conditions, where the gel network is used as a reducing and particle stabilizing agent. We show that the dynamics of the self-assembly process, controlled by the rate of catalysis, can direct the shape and size of the gold nanostructures to influence their inherent optoelectric properties, which is crucial for their application in bionanotechnology. We use a range of spectroscopic and microscopic techniques to follow these structural changes. Such spatially controlled organization of metal nanoparticles into hybrid nanostructures can be of interest in construction of nanoscale electronic devices. References: Chem. Commun., 2011, 47, 728-730; Chem. Mater., 2007, 19, 138-140; J. Mater. Chem., 2010, 20, 6696-6702.
5:45 AM - OO5.9
Protein-based Sporicidal and Bactericidal Materials
Matthew B. Dickerson 1 Wanda Lyon 2 Alexandra Sierra 1 William E Gruner 2 Peter A Mirau 1 Joseph M Slocik 1 Michael L Jespersen 1 Rajesh R Naik 1
1Air Force Research Laboratory Wright Patterson AFB USA2Air Force Research Laboratory Wright Patterson AFB USAShow Abstract
Materials capable of mitigating potentially harmful biological agents are highly desirable and are under active development for use in self-decontaminating coatings, textiles, filters, and protective equipment. Although many routes to self-cleaning and self-decontaminating materials have been achieved during the last decade, the production of these materials often requires sophisticated chemical synthesis techniques and manufacturing facilities. Furthermore, many of the antimicrobial materials and surface treatments currently available are ineffective against or slow to kill bacterial spores, such as those of the Bacillus genus. In our work, we report on the development of a facile approach to create potent antimicrobial materials from protein-based textiles and composite materials. Our results demonstrate that chemically modified fibroin- and keratin-based materials that induce >5 Log reduction in the colony forming units of Escherichia coli, as well as Bacillus thuringiensis Al Hakam spores and cells within 10 min of organism-material contact. The effects of processing parameters on the antimicrobial potential and mechanical strength of the treated protein-based materials will be presented.
OO4/RR4: Joint Session: Interfaces in Bio-enabled Materials
Wednesday AM, April 11, 2012
Marriott, Yerba Buena, Salons 12-13
9:30 AM - *OO4.1/RR4.1
Chemomechanics at the Cell-material Interface: From Molecular-scale Binding to Cell-scale Functions
Krystyn J. Van Vliet 1 2
1MIT Cambridge USA2MIT Cambridge USAShow Abstract
The interface between biological cells and adjacent materials -- which include other cells, extracellular matrices, and drug-delivery vehicles -- is spatially and temporally dynamic. As the physical connection between the cell microenvironment and internal protein networks, the cell-material interface is also a prime example of chemomechanical coupling: small changes in either local chemical or mechanical cues can result in significant changes in cell organization and function. Here, we will discuss our recent work in understanding how extracellular cues such as macromolecular concentrations, pH, and effective matrix stiffness affect functions of tissue and stem cells ranging from adhesion to migration to differentiation of new biological functions. We will focus on the new experimental, analytical, and computational tools that we have developed to interrogate this interface from the molecular to the cell scale -- particularly in the context of soft-tissue diseases and cancer -- and to design new strategies that manipulate cell behavior directly by engineering of this buried interface.
10:00 AM - OO4.2/RR4.2
Label-free and Viable Stem Cell Isolation from Peripheral Blood with a Thermoresponsive Microfluidic Chip
Umut A Gurkan 1 2 Huseyin Tas 1 2 Tarini Anand 1 2 Utkan Demirci 1 2
1Brigham and Womenrsquo;s Hospital, Harvard Medical School Cambridge USA2Harvard-MIT Health Sciences and Technology Cambrirdge USAShow Abstract
Effective, easy to use, inexpensive, and rapid selective label-free cell isolation technologies are significantly needed to enable a new era of down-stream processing of stem cells for broad applications in tissue engineering, regenerative medicine, biological research and diagnosis of diseases. Isolation of stem cells (e.g., CD34+ endothelial progenitor cells) from peripheral blood, cord blood, and bone marrow has found significant applications in regenerative medicine and tissue engineering. Fluorescence-activated and magnetic-activated cell sorting are commonly used methods for cell isolation, which require extensive preliminary sample processing and tagging of the cells with fluorophores or magnetic particles conjugated with antibodies. While these methods are powerful and sort cells from heterogeneous mixtures, the cost, complexity and the requirement for infrastructure limit their use at the point-of-care (POC). Here we present a disposable, easy to fabricate microfluidic chip to retrieve label-free viable CD34+ stem cells from peripheral blood without any pre-processing in less than 10 minutes, which can also be used at the POC. We have developed a biotin binding protein (Neutravidin) and biotinylated antibody based surface chemistry on temperature responsive polymer (pNIPAAm) layered microfluidic channels. Whole blood was flown through the channels without any preliminary processing. The CD34+ cells were captured on the channel surface with antibody-antigen interaction. The non-captured cells in the channels were rinsed away with buffer solution. Captured cells were then released from the surface by reducing the temperature to <32C. The released cells were analysed for viability (live/dead assay) and cultured in vitro. The CD34+ cells in the whole blood samples were quantified by flow cytometry by using calibration and counting beads. We have specifically captured and controllably released the rare CD34+ stem cells from peripheral blood, which were quantified to be 19 cells per million blood cells in the patient whole blood samples used in this study. We achieved a capture specificity of 89% (Â±12%) and a release efficiency of 82% (Â±15%). Our results indicated that CD34+ cells released from the microchannels were viable (>90%) and amenable for in vitro cultivation. Although cell capture methods have been demonstrated in microfluidic systems, the release of captured cells remains as a significant challenge. We have shown that cells can be rapidly, controllably released in microchannels with high viability and specificity after they were selectively label-free captured from blood without any pre-processing. The controlled release of live cells that are selectively captured from heterogeneous cell suspensions, biological and bodily fluids can generate a great impact in areas such as stem cell isolation/purification for regenerative therapies, genomic/proteomic analysis, and circulating rare tumor cell isolation for cancer research.
10:15 AM - OO4.3/RR4.3
Materials Properties and In vivo Studies of Ultrananocrystalline Diamond (UNCD) Biocompatible Coating for Dental Implants
Pablo Gurman 1 Marcos E Bruno 2 3 Deborah R Tasat 2 4 Daniel G Olmedo 3 5 M. Sittner 2 Maria B Guglielmotti 3 5 Romulo L Cabrini 3 6 Alejandro Berra 7 Orlando Auciello 1
1Argonne National Laboratory Lemont USA2UNSAM San Martiacute;n Argentina3FOUBA CABA Argentina4FOUBA CABA Argentina5CONICET CABA Argentina6CNEA CABA Argentina7Facultad de Medicina,UBA CABA ArgentinaShow Abstract
Pure titanium and titanium alloys are widely used in orthopedic and dental implants because on their desirable mechanical properties and biocompatibility. However, these materials suffer from electrochemical corrosion when implanted in the mouth, which induces release of metallic particles from the titanium surface, promoting inflammation around the implant, and implant failure, which was associated to the presence of macrophages in peri-implant soft tissue . A novel ultrananocrystalline diamond (UNCD) thin film developed and patented at Argonne National Laboratory exhibit excellent bionert/biocompatible properties and strong resistance to chemical attack as coating for implantable biomedical devices, as recently shown for encapsulation of a Si microchip implantable in the eye to restore sight to people blinded by retina degeneration . Therefore, we are investigating UNCD coatings for dental implants, because their high resistance to chemical corrosion, strong mechanical resistance and biocompatibility. The UNCD coating acts as a protective barrier between the implant and the biological environment, which would prevent the release of metallic ions from titanium implants into the body. In order to assess the potential of UNCD as a coating for titanium dental implants, we investigated the osteointegration rate of titanium, UNCD-coated titanium, and UNCD/W-coated titanium implants using the rat diaphyseal tibia as a model to study osteointegration, relevant to dental implants. Titanium laminar implants (Implant-Vel, Buenos Aires, Argentina) were coated with the three type of layers indicated above and used to study the osteointegration rate in the diaphysis of the tibia bone of rats, simulating the maxilar bone of the mouth cavity. All animal experiments were carried out following NIH guidelines for the care and use of laboratory animals. Macroscopic observations revealed that wound healing was occurring satisfactorily in all specimens and all implants remained in situ in the diaphyseal areas. Subsequently, the implants were extracted after 14 days of implantation and histological sections were prepared and analyzed via Optical Microscopy. The optical pictures showed laminar bone formation on the surfaces of the three groups studied. Histological results, from short term experiments, indicated that UNCD and UNCD/W coatings of dental implants are well tolerated by the surrounding tissue and did not elicit any inflammatory reactions, similarly to Ti implants without coating. However, the corrosion observed in long-term Ti dental implants and the total inertness of UNCD coatings, as shown in long term in vivo animal eyes studies, indicate that UNCD-coated dental implants will outperform bare Ti or Ti-alloy implants. Work is in progress to perform long term in vivo studies of UNCD-coated dental implants. 1. D. Olmedo et al, Imp Dent vol 12 (2003) 75. 2. X. Xiao / O. Auciello et al., J. Biomedical Materials 77B (2006) 273.
10:30 AM - OO4.4/RR4.4
Cellularized Polymeric Detachable Platform for Blood Vessel Reconstruction
Halima Kerdjoudj 3 Armelle Chassepot 4 Patrick Menu 5 Pierre Schaaf 1 2 Jean-Claude Voegel 4 Benoit Frisch 5 Fouzia Boulmedais 1 2
1CNRS Strasbourg France2Universiteacute; de Strasbourg Strasbourg France3INSERM Reims France4INSERM Strasbourg France5CNRS Nancy FranceShow Abstract
Development of blood vessel remains a big challenge for vascular tissue engineering. We recently demonstrated that poly(allylamine hydrochloride)/poly(styrene sulfonate) (PAH/PSS) films constitute excellent substrates for vascular progenitor cell differentiation. However, no intact cell sheets could be harvested. Using a spraying procedure, we develop a user friendly technology for the development of small blood vessels based on alginate membranes. The key point of our approach is based on a multilayered PAH/PSS film built on micro-textured alginate gels, about 140 Âµm thick and which can be peeled off. The alginate, calcium chloride and polyelectrolyte solutions are sprayed on a vertical glass substrate to obtain an oriented micro-textured gel. The PAH/PSS film, built on top of the gel, induces a good proliferation without phenotype alteration of Smooth Muscle Cells (SMC) and Human Gingival Fibroblasts. Parallel running micro-textures on the top of the gel allow the orientation of SMC cells. After peeling off the substrate, the cellularized membrane could be rolled around a mandrel or cultured later on showing a good retention of differentiated cells shapes after 10 days of culture. This work represents the initial stages of a new, original blood vessel reconstruction strategy via tissue engineering.
10:45 AM - OO4.5/RR4.5
Synthetic Protein Targeting by the Intrinsic Biorecognition Functionality of Polyethylene Glycol Using PEG Antibodies as Biohybrid Molecular Adaptors
Janne T Hyoetylae 1 Jie Deng 2 Roderick Y. H. Lim 1
1University of Basel Basel Switzerland2A*STAR (Agency for Science, Technology and Research) Singapore SingaporeShow Abstract
Interfaces capable of biological recognition and specificity are sought after for conferring bioinspired functionality onto synthetic biomaterials systems. Here, we demonstrate how intrinsic polymerâ?"protein interactions between highly localized polyethylene glycol (PEG) brushes and PEG-binding antibodies (anti-PEG) can be used for sorting specific biomolecules from complex bulk biological fluids to synthetic nanoscale targets. A principal feature lies with the antifouling property of PEG that prevents unspecific binding. As a means to replicate the cellular property of protein targeting, exclusive access is provided by anti-PEG, which acts as a biohybrid molecular adaptor that sifts out and targets a model IgG "cargo" from solution to the PEG. The PEG target sites can be reversibly washed and targeted in blood serum, which suggests potential benefits in technological applications such as biosensing and biomarker detection. Moreover, anti-PEG binding triggers a stimuli-responsive conformational collapse in the PEG brush, thereby imparting an intrinsic "smart" biorecognition functionality to the PEG that can considerably impact its use as an antifouling biomaterial. This stimuli-responsive behavior can be harnessed to create bio-inspired nanoporous membranes, which allow for the exclusive transport of specific molecular species via biochemical recognition.
11:30 AM - *OO4.6/RR4.6
Pragmatic Approaches for Modelling Structures of Bio-interfaces Using Advanced Sampling
Tiffany R. Walsh 1 2 Louise B Wright 1 2
1University of Warwick Coventry United Kingdom2University of Warwick Coventry United KingdomShow Abstract
While many different peptide sequences have now been identified to have strong affinity for a huge range of inorganic materials, the question of why a given peptide sequence binds so well while another does not remains to be properly answered. So too does the question of how the binding structure of the biomolecule impacts on the properties of the interface. To address these questions will enable significant advances in the fabrication of bio-inorganic interfaces with controllable, multi-functional properties. Application of molecular simulation to model these interfaces is one of many complementary techniques that enables us to investigate these phenomena. A key challenge for molecular simulation in this area is to achieve sufficient conformational sampling of the peptide in this aqueous interfacial environment. In this contribution, a summary of our recent work probing the effectiveness of advanced sampling approaches, namely Replica Exchange Molecular Dynamics, and variants of this method, will be presented, with examples taken from the quartz-binding peptide system.
12:00 PM - OO4.7/RR4.7
Peptide Isomerase-like Activity of Gold Nanoparticles
Joseph Slocik 1 Patrick B Dennis 1 Rajesh R Naik 1
1AFRL Dayton USAShow Abstract
The chiral biasing of proteins towards only L-amino acid configurations from a racemic mixture is a fundamental paradigm in biology. To date, there has been some speculation and recent evidence to suggest that differential hydration, preferential crystallization, chiral selection by minerals, and the presence of right circularly polarized light on earth may have had an impact in the evolutionary selection of L- over D-amino acids. It is also believed that inorganic matrices may have played a substantial role in producing left-handed protein structures in nature beyond simple chiral selection by acting both as a catalytically active and chiral surface for D-amino acid containing peptides and proteins. For example, silver NPs have been implicated in the conversion of right-handed DNA to left-handed DNA; while metal ions have been used to post-translationally modify L-amino acids into D-amino acid peptides. In this study, we show that a right-handed peptide composed of all D-amino acids undergoes an optical and chemical transition to the left-handed L-form in the presence of gold nanoparticles. This chiral conversion activity of nanoparticles will likely expand the tunability and scope of metamaterials as well as provide a platform for chiral sensing.
12:15 PM - OO4.8/RR4.8
The Structure of Peptides at Metal and Metal-oxide Surfaces Probed by NMR
Peter A Mirau 1 Michael Kotlarchyk 2 Hilmar Koener 1 Richard A Vaia 1 Rajesh Naik 1
1Air Force Research Laboratories Wright-Patterson AFB USA2Rochester Institute of Technology Rochester USAShow Abstract
Peptides that bind inorganic surfaces and template the formation of nanometer-sized inorganic particles are of great interest for the self- or directed assembly of nanomaterials for sensors and diagnostic applications. These surface-recognizing peptides can be identified from combinatorial phage-display peptide libraries, but little experimental information is available for understanding the relationship between the peptide sequence, structure at the nanoparticle surface and function. We have developed NMR methods to determine the structures of peptides bound to inorganic nanoparticles and report on the structure of peptides bound to silica, titania and palladium nanoparticle surfaces. Samples were prepared under conditions leading to rapid peptide exchange at the surface such that solution-based nuclear Overhauser experiments can be used to determine the three-dimensional structure of the bound peptide. The binding motif for the silica and titania binding peptides is defined by a compact "C"-shaped structure for the first six amino acids in the 12-mer. The orientation of the peptide on the nanoparticle surface was determined by magnetization transfer from the nanoparticle surface to the nearby peptide protons. Broader lines are observed for the Pd4 12-mer peptide bound to 2 nm Pd particles. 2D NMR methods are developed to estimate the separation of the amino acid protons from the metal surface in Pd4 and in single and double mutants with alanine in place of histidine at amino acids 6 and 11. The results show that the peptide bulges out from the metal surface at the mutation site. Pulse-field gradient diffusion and x-ray scattering experiments show that the Pd nanoparticle solutions are stable for months and that the peptide is not exchanging on and off the surface of the nanoparticles on the time scale of the NMR experiments. These methods can be applied to a wide variety of abiotic interfaces to provide an insight into the relationship between the primary sequence of peptides and their functionality at the interface.
12:30 PM - *OO4.9/RR4.9
LbL Polymeric Nanoshells for Controlled Wrapping of Anisotropic Crystals and Cells
Vladimir Tsukruk 1
1Georgia Tech Atlanta USAShow Abstract
We report on designing highly permeable and robust nanoscale gel shells for cells, cell assemblies, spherical microparticles, and anisotropic inorganic crystals. These responsive nanoshells are formed through a layer-by-layer assembly based upon hydrogen-bonding, ion pairing, hydrophobic-hydrophobic interactions, and components interdiffusion. These LbL shells can be reinforced via physical or covalent crosslinking by inclusion of nanoparticles, inducing local crystallization, or adding crosslinking agents. These shells are exploited to control and tune the permeability and robustness of the nanoshells. We demonstrated that the nanoshells support high viability of the cells with minor effect of growth and dividing of cells especially if a cationic component is screened or completely removed. We discuss significance of multilayer shell morphologies for designing novel vehicles with tunable loading-unloading properties and enhanced robustness.