Norman Wagner University of Delaware
Gerald G. Fuller Stanford University
Jennifer Lewis University of Illinois, Urbana-Champaign
Ko Higashitani Kyoto University-Katsura
W1: Self-Assembly of Colloidal Crystals I
Monday PM, April 17, 2006
Room 2001 (Moscone West)
9:00 AM - **W1.1
On-chip Manipulation by Electric Fields: From Self-Assembling Particles to Self-Propelling Devices
Orlin Velev 1 , Suk Tai Chang 1 , Vesselin Paunov 2 Show Abstract
1 Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Department of Chemistry, University of Hull, Hull United Kingdom
We have demonstrated previously how dielectrophoresis, particle interaction with external AC fields, can be used to manipulate and assemble colloidal particles on any size scale, from nanometer gold particles, to submicron sized latex, to millimeter sized droplets. The structures that can be assembled by these methods include, for example, microwires, switchable photonic crystals, and complex anisotropic supraparticles. We will demonstrate here that an additional level of complexity can be engineered to turn the particles into prototypes of self-propelling micromachines. We show how various types of miniature semiconductor diodes floating in water can propel themselves when an uniform alternating electric field is applied across the container. The millimeter-sized diodes generate electroosmotic force, which propels them in the direction of either the cathode or the anode depending on the surface charge of the particles. The electroosmotic velocity depends on the electrolyte concentration and pH of the solutions. The velocity of the particles, however, does not depend strongly on their size; the electrokinetic mobility could, in principle, be used to propel particles or devices on the microscale. The diode motility can be used to power rotating "gears" and can be controlled by light. Thus, diodes propelling in electric fields suggest rudimentary solutions to problems facing self-propelling microdevices, including harvesting power from external sources, internally controlled movement, and potential for a range of additional functions.
9:30 AM - W1.2
Utilizing the Electronic Industry's Tricks for Transistor Fabrication for Development of New Delivery Colloidal Vehicles for Nanomedicine Applications
Larken Euliss 1 4 , Christopher Welch 2 , Stephanie Gratton 1 4 , Benjamin Maynor 1 4 , Klaus Hahn 2 4 , Rudy Juliano 2 4 , Joseph DeSimone 1 3 4 Show Abstract
1 Chemistry, University of North Carolina Chapel Hill, Chapel Hill, North Carolina, United States, 4 Lineberger Comprehensive Cancer Center, University of North Carolina Chapel Hill, Chapel Hill, North Carolina, United States, 2 Pharmocology, University of North Carolina Chapel Hill, Chapel Hill, North Carolina, United States, 3 Chemical Engineering, North Carolina State University, Raleigh, North Carolina, United States
The delivery of therapeutic, detection and imaging agents for the diagnosis and treatment of cancer patients has improved dramatically over the years with the development of nano-carriers such as liposomes, micelles, dendrimers, biomolecules, polymer particles, and colloidal precipitates. While many of these carriers have been used with great success in vitro and in vivo, each suffers from serious drawbacks with regard to stability, flexibility, or functionality. To date, there has been no general particle fabrication method available that afforded rigorous control over particle size, shape, composition, cargo and chemical structure. By utilizing the method we has designed referred to as Particle Replication In Non-wetting Templates, or PRINT, we can fabricate monodisperse colloidal particles with simultaneous control over structure (i.e. shape, size, composition) and function (i.e. cargo, surface structure). Unlike other particle fabrication techniques, PRINT is delicate and general enough to be compatible with a variety of important next-generation cancer therapeutic, detection and imaging agents, including various cargos (e.g. DNA, proteins, chemotherapy drugs, biosensor dyes, radio-markers, contrast agents), targeting ligands (e.g. antibodies, cell targeting peptides) and functional matrix materials (e.g. bioabsorbable polymers or stimuli responsive matrices). PRINT makes this possible by utilizing low-surface energy, chemically resistant fluoropolymers as molding materials and patterned substrates to produce functional, harvestable, monodisperse polymeric particles.To demonstrate the potential and compatibility of PRINT for introducing “soft” molecular recognition moieties and/or valuable therapeutic agents into functional particles, we have encapsulated oligonucleotide and protein cargos within them to generate monodisperse “particle devices.” We have incorporated fragile biological cargos and recognition agents, i.e. DNA, proteins (fluorescently-labeled avidin (MW 68 kDa)), and small anti-cancer agents (doxorubicin) into PEG nanoparticles using the simple, mild and general PRINT technique. We have arguably generated DNA delivery vectors that are themselves first generation “synthetic viruses” (monodisperse populations of shape-specific particles containing DNA). Furthermore, these biomolecule-containing particles could be used as nanoscale, shape-specific biosensors or next-generation therapeutic agents. We were able to confirm the encapsulation of the oligonucleotides by observing fluorescence from monodisperse particles using confocal microscopy.PRINT has several distinct advantages over other vector fabrication techniques in that the particles are monodisperse and shape specific. In addition, no surfactants condensation agents, etc. are required.
9:45 AM - W1.3
Structure and Dynamics of Bbiphasic Colloidal Suspensions.
Ali Mohraz 1 , Eric Weeks 2 , Jennifer Lewis 1 Show Abstract
1 Materials Science and Engineering, Univeristy of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Physics, Emory University, Atlanta, Georgia, United States
We investigate the structure and dynamics of concentrated biphasic mixtures comprised of attractive and repulsive silica microspheres using confocal laser scanning microscopy. One population of colloids is rendered hydrophobic by chemically modifying their surface. These species flocculate when suspended in an index-matching (water-DMSO) solvent, while their unmodified (charge-stabilized) counterparts remain individually dispersed.By labeling the two microsphere populations with different fluorescent dyes, we can directly image the flocculated and dispersed phases independently. The structural and dynamical parameters salient to the mixture’s rheology are quantified as a function of total colloid volume fraction and different ratios of the two phases. These results will provide new insights into the development of concentrated colloidal inks for direct-write assembly of complex 3D structures.
10:00 AM - W1.4
Coulomb Blockade at Room Temperature in Nanoparticle Arrays Aligned on DNA Scaffolds
Gregory Kearns 1 2 , James Hutchison 1 2 Show Abstract
1 Chemistry, University of Oregon, Eugene, Oregon, United States, 2 Materials Science Institute, University of Oregon, Eugene, Oregon, United States
Nanoparticles are of great interest as components in new materials and devices due to their size dependent optical and electronic properties. Two significant challenges in developing nanoparticle-based devices are assembling nanoparticles in a useful way and bridging nanoscale assemblies to microscale electronics. We have developed methods to form linear arrays of 1.5 nm particles that can be easily integrated with the microscale in order to exploit the properties of the nanoscale components while allowing access to the devices through microscale contacts. Metal nanoparticles with core diameters of less than 2 nm exhibit Coulomb blockade at room temperature, which can be used to develop new electronic devices such as single electron transistors (SET). These devices offer several advantages over semiconductor-based transistors—(i) they are 1-2 orders of magnitude smaller than current state-of-the-art transistors, (ii) SETs are not hindered by electron tunneling that can lead to device heating and/or failure in semiconductor based transistors, and (iii) it is possible to use a greener, bottom-up assembly approach to develop complex structures.We have developed a convenient synthetic route to monodisperse 1.5 nm gold nanoparticles that can be functionalized with a wide range of ligand shells. Using these particles, we have shown that, in solution, nanoparticles can be organized into linear arrays using electrostatic interactions between the negatively charged backbone of DNA and the positively charged ligand shell of functionalized nanoparticles. These interactions result in extended linear chains of close-packed nanoparticles. Close-packing of the nanoparticles on the DNA scaffold allows precise control over interparticle spacing by the appropriate choice of ligand shell. In order to make useful devices of these arrays, we have been working to align DNA on surfaces prior to coating with nanoparticles in order to obtain parallel, linear arrays of nanoparticles. Using specially fabricated TEM grids composed of a silicon grid with thermally grown, electron transparent SiO2 windows, we have shown that we can make long-range (tens of microns) parallel arrays of nanoparticles on thermal SiO2 in a three step assembly process involving (i) silanization of the SiO2 surface, which promotes molecular combing of DNA and limits nonspecific adsorption of positively charged nanoparticles, (ii) molecular combing of DNA on the silanized surface, and (iii) nanoparticle assembly on the linear arrays of DNA. TEM analysis of these arrays shows that the arrays are parallel over the entire substrate and that high purity nanoparticles maintain their core size and spacing as determined by the thickness of the ligand shell. With these arrays we have developed electronic test structures that exhibit Coulomb blockade at room temperature.
10:15 AM - W1.5
Dewetting Induced Formation of Nanoparticle Stripe Patterns.
Jiaxing Huang 1 2 , Franklin Kim 1 2 , Andrea Tao 1 2 , Stephen Connor 1 2 , Peidong Yang 1 2 Show Abstract
1 Department of Chemistry, UC-Berkeley, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
10:30 AM - W1.6
Generalized Rule for Order Formation by Colloidal Nanoparticles Adsorbed on a Substrate.
Minoru Miyahara 1 , Satoshi Watanabe 1 Show Abstract
1 Chemical Enginering, Kyoto University, Kyoto Japan
Ordered arrays of particles have been attracting much attention recently because of their unique functions especially as optical devices. We performed Brownian dynamics simulations of adsorption of electrostatically stabilized colloidal particles and their spontaneous order formation on a planar surface with countercharge, in which the particle–particle and particle–substrate interactions are modeled based on the DLVO theory. The results obtained are: (1) A hexagonally ordered array by adsorbed particles is found to form only if a controlling factor, the “average force” acting between adsorbed particles, exceeds a limiting value that is common to various ionic strengths; (2) A general concept extended from the Alder transition is proposed to give a comprehensive understanding of the characteristics of the “average force”, with which the controlling factor and resultant ordered structure can be predicted a priori for any combination of temperature, ionic strength and particle size. Further, large-scale simulations were performed to observe time-evolution of ordered domains and their merging processes, which exhibited two types of different behaviors depending upon the Debye lengths or ionic strengths: one type with easily merging domains and the other one with prevailing domain structures. The origin of the difference will be discussed in connection with the "average force" and the characteristics of the particle-substrate interactions.
10:45 AM - W1.7
Regulation of Atomic Alignment in Superlattices of Au and Ag Nanoparticles.
Keisaku Kimura 1 , Yang Yang 1 , Suhua Wang 2 , Seiichi Sato 1 , Hiroshi Yao 1 Show Abstract
1 Graduate School of Science, University of Hyogo, Hyogo Japan, 2 Department of Chemistry, National University of Singapore, Singapore Singapore
Intense research interest is focusing on the nano-sized substances such as surface modified gold and silver nanoparticles, nanodiscs and nanowires due to their notable electronic and optical properties based on the quantum size effect. Fabrication of macroscopic architecture using these nano-sized materials as a constructing block will be a next target in the coming nanotechnology era. There are many reports on the construction of two and three-dimensional superlattices made by metallic nanoparticles, because it will provide a peculiar performance based on collective electronic behaviors resulting from interparticle interactions between neighboring ordered particles. In order to accomplish an ultimate collective motion of electrons or excitation energy moving this ordered structure, we need atomic orientational as well as translational alignment in the superlattice. While regular lattices made of nanoparticles are prepared by spontaneous evaporation of organic solvent in most cases, we have developed a new class of superlattice at an air/water interface by virtue of the ionic or hydrogen bonding interactions under an equilibrium condition . It was found that water cluster exist interstitially in the superlattice spacing observed by FTIR at room temperature . At the same time, some arc patterns in the diffraction from atoms superimposed with the diffraction from superlattice were observed in the transmission electron diffraction (TED), suggesting atomic orientational arrangements to some extent in this small crystal. We will present more complete TED pattern that shows coexistence of atomic and superlattice orientational alignment in the crystal.Two metallic nanoparticles, gold and silver, were used to construct nanoparticle assemblies. For a typical preparation of gold nanoparticles at thiol to gold ratio = 3, 0.5 mmol of HAuCl4 aqueous solution was mixed with 1.5 mmol of MSA in 100-mL methanol. A freshly prepared 0.2 M ice-cold aqueous NaBH4 solution (25 mL) was then added under vigorous stirring. After further stirring for 1h, the precipitate was gathered by decantation and centrifugation. The precipitate was washed with water/methanol solution and then with pure methanol and ethanol. Finally, the sample was obtained as a solid powder by freeze-drying. The mean particle diameter was typically 3.5 nm (fwhm: 0.4 nm). The crystallization took place at an air/water interface in 4-10 days in the presence of an appropriate amount of hydrochloric acid in a sealed vial giving numerous micrometer-sized nanoparticle crystals with clear crystal habit [1,2]. The TED and TEM images were taken by a Hitachi H8100 transmission electron microscope. Samples were set on the amorphous carbon film on the Cu grid. The observed TED pattern is discussed along with the sample preparation treatment.. K.Kimura, S.Sato and H.Yao, Chem.Lett., 2001, 372-373.. S.Wang, H.Yao, S.Sato and K.KimuraJ.Amer.Chem.Soc. 126(24)(2004)7438-7439.