Carlos J. Martinez Purdue University
Sonia Grego RTI International
Alberto Fernandez-Nieves Georgia Institute of Technology
Joao Cabral Imperial College London
KK1: Biological Applications
Tuesday PM, April 06, 2010
Room 3014 (Moscone West)
9:15 AM - **KK1.1
High-throughput Droplet Microfludics for Chemical and Biological Synthesis.
Andrew de Mello 1 Show Abstract
1 Chemistry, Imperial College London, London United Kingdom
Rapidly evolving frontiers in genomics, proteomics and medical diagnostics generate an ever-increasing demand for high throughput analytical information. The ability to extract the required information from a chemical or biological system almost always involves performing a number of distinct analytical operations. In principle, microfluidic systems may incorporate all such relevant steps including sample handling, sample pre-treatment, reaction, product separation, analyte detection, and product isolation. While downsizing, system integration and parallelisation afford many performance gains including speed, analytical efficiency and throughput, new problems are also encountered.Droplet-based microfluidic systems that utilize flow instabilities between immiscible fluids have been the subject of much interest in recent years and have been exploited in a diverse range of chemical and biological applications. As aqueous droplets within segmented microflows define confined volumes in the femto- or picolitre range, they have the potential to serve as isolated reaction compartments for both screening and synthetic purposes.My talk will discuss how droplets formed spontaneously when multiple laminar streams of aqueous reagents are injected into an immiscible carrier fluid, can be used for synthetic applications including nanomaterial synthesis and PCR. Additionally, I will discuss novel microfluidic elements for both droplet merging and high-throughput serial droplet dilution. Both devices exploit the difference in hydrodynamic resistance of the continuous phase and the surface tension of the discrete phase through the use of passive structures contained within a microfluidic channel.
10:00 AM - KK1.3
Microfluidic ELISA for Ocular Diagnostics.
James Green 1 , Shashi Murthy 1 Show Abstract
1 Chemical Engineering, Northeastern University, Boston, Massachusetts, United States
Uveitis and primary intraocular lymphoma (PIOL) are diseases associated with the invasion of lymphocytes into various regions of the eye. Both conditions may be caused by diseases outside the eye or within ocular tissue and both cause the same types of symptoms. A detailed diagnosis is critical for the early detection of PIOL as well as for identifying targeted therapeutic drugs to treat uveitis. The current diagnostic tests carried out following a vitreous biopsy include enzyme-linked immunosorbent assay (ELISA), flow cytometry and analysis by a skilled pathologist. Despite the array of diagnostic tests, the ‘diagnostic yield’ is only approximately 20% and this low statistic can be attributed to the lack of sensitivity within these diagnostic tests.The microfluidic approach is a valuable alternative to the current approach because of its ability to handle small sample volumes and quantitatively detect small (picomolar) quantities of cytokines. Furthermore, microfluidic systems can be operated in clinical settings and provide a quick readout, eliminating the need to transport biopsy samples to institutional laboratories and delays in analysis. This presentation will describe how a simple microfluidic channel complete with antibody-coated vertical pillars was used to perform a traditional sandwich-ELISA to measure the cytokine content of the aqueous humor during endotoxin-induced uveitis in a rat. The significance of this approach is that the technology may be able to offer a point-of-care diagnostic device that is capable of determining the cytokine content in a patient’s vitreous biopsy. Furthermore, this approach could be an effective way to accurately measure and map the full cytokine profiles of vitreous biopsies from patients that have either uveitis or PIOL.
10:15 AM - KK1.4
Gene Regulatory Study on a Chip: Pseudomonas Aeruginosa as a Model System.
Jing Dai 1 , Jae Young Yun 1 , Jong Wook Hong 1 Show Abstract
1 Mechanical Engineering, Auburn University, Auburn, Alabama, United States
Pseudomonas aeruginosa is an opportunistic human pathogen that can sense its own population density and alter its behavior, such as production and secretion of virulence factors, by using cell-to-cell signaling system. This system is controlled by the expression of regulatory genes in las and rhl systems. To assess the gene regulatory mechanism of cell-to-cell signaling in systematic manner, we developed a novel microfluidic platform which is capable of bacterial growth and bacterial growth monitoring. We utilized the green-fluorescent protein (GFP) fusion reporter system for non-destructive, real-time quantification of specific gene expression which is regulated by las and rhl systems. Based on gene expression analysis with the reporter system, we assessed the relationship between the deficiency of regulatory gene in las and rhl systems (genotype) and the level of the gene expression of virulence genes lasA, lasB (phenotype). Consequently, the effect of each regulatory gene in cell-to-cell signaling system on the expression of downstream gene was quantitatively and systematically assessed. This microfluidic platform could contribute to improve the current knowledge of the regulatory mechanism of cell-to-cell signaling in P. aeruginosa and to help the systematic assessment of the gene regulation of other bacteria, as well as multi-cellular organism such as animal and human cells.
10:30 AM - KK1.5
Microfluidic Synthesis of Membrane Proteins for an Olfactory Receptor-based Odorant Biosensor.
David Kong 1 , Brian Cook 2 , Eddie Liu 2 , Karolina Corin 2 , Shuguang Zhang 2 , Joseph Jacobson 1 Show Abstract
1 Media Lab, MIT, Cambridge, Massachusetts, United States, 2 Bioengineering, MIT, Cambridge, Massachusetts, United States
Animal noses have evolved the ability to rapidly detect small airborne and soluble molecules at minute concentrations. Furthermore, the range of odorants detected is chemically diverse and seemingly infinite. Olfactory receptors (ORs), the key component to mammalian scent detection, have been synthesized in a microfluidic device for use as the sensing module for a novel odorant biosensor. The microfluidic production of these olfactory receptors is also, to our knowledge, the first demonstrated synthesis of any membrane protein in a microfluidic environment.Membrane proteins are amongst the most important classes of proteins in living systems, accounting for ~30% of genes in almost all sequenced genomes. However, our ability to understand their structure and function or ability to utilize and engineer them is hampered by how notoriously difficult they are to synthesize. In this work, we demonstrate, to our knowledge, the first syntheses of olfactory receptors in a microfluidic environment. A panel of several ORs was fabricated in a PDMS-based microfluidic device given inputs of DNA, cell lysates, and detergents for membrane protein stabilization. The device featured two reactors ~250 nL in volume along with on-chip mixers which enabled reactor agitation during synthesis. The syntheses were successfully verified by Western blot, fluorescence spectroscopy, and circular dichroism. This module for on-chip OR production is further being integrated with a module for microfluidic gene synthesis . In this paradigm, instead of inputs of OR genes, short, chemically synthesized DNA oligonucleotides are injected along with PCR reagents to first synthesize the desired OR gene, followed by the integrated on-chip production of membrane protein. Lastly, this on-chip OR production module is being integrated with several signal transduction techniques including dieletric spectroscopy and speckle interferometry  for the low-concentration detection of odorants. D.S. Kong, P.A. Carr, L. Chen, S. Zhang, J.M. Jacobson, “Parallel gene synthesis in a microfluidic device,” Nucleic Acids Res 35: e61, 2007.Pappu et. al., “Physical One-Way Functions,” Science, 297, 2001.
10:45 AM - KK1.6
Towards Cell Capture and Isolation: Derivation and Modeling of Forces on a Magnetically Labeled Cell Within a Microfluidic Device Design.
Brian Plouffe 1 , Dattatri Nagesha 2 , Shashi Murthy 1 , Laura Lewis 1 Show Abstract
1 Chemical Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Physics, Northeastern University, Boston, Massachusetts, United States
Cell separation techniques can be broadly classified into two categories: those based on size and density, and those based on affinity (chemical, electrical, or magnetic). Techniques that achieve separation based on size and density are generally unable to provide adequate resolution between populations known to be of similar size. On the other hand, in fluorescence activated cell sorting (FACS), antibodies tagged with fluorescent dyes are attached to cells in mixed suspensions via receptor-ligand binding. In addition to FACS, labeling using antibody-coated paramagnetic micron size magnetic beads is an alternative separation methodology. Magnet-activated cell sorting (MACS) allows target cells to be processed in parallel, allowing faster separation of high-purity cell populations. Microfluidic channels allow for the analysis of significantly smaller sample volumes while maintaining comparable purity. Unfortunately the current state of the art is still limited in throughput in comparison to other continuous flow methods. Additionally, using micron size beads result in uncontrolled binding characteristics and changes of the phenotype and gene expression of the cell. These shortcomings illustrate the need for the development of a high throughput continuous flow separation device, as well as a reduction of the particle size in order to better control the cell phenotype. The following work illustrates the application of a mathematical model towards the development of a separation device as a methodology for cell isolation for applications in biology and medicine. The design parameters for a microfluidic cell capture and separation device based on magnetic field deflection-based cell capture are derived. Adjustable parameters such as flow rate, channel dimensions, and magnetic field strength are considered and optimized to produce a cell isolation device.
KK2: Screening and DNA
Tuesday PM, April 06, 2010
Room 3014 (Moscone West)
11:30 AM - KK2.1
A High Density Multiplexing Approach for Rapid, Informative Plasma Protein Detection in Cancer Diagnostics and Ordered, Pinpoint Cell Assembly in Tissue Engineered Structures.
Ophir Vermesh 1 , Udi Vermesh 2 Show Abstract
1 Chemistry, California Institute of Technology, Pasadena, California, United States, 2 Bioengineering, California Institute of Technology, Pasadena, California, United States
The DNA-Encoded Antibody Libraries (DEAL) technique for transforming DNA microarrays into antibody arrays has demonstrated unique advantages in facilitating the integration of microfluidic systems with highly multiplexed biological sensing for point-of-care diagnostics. In particular, by using microfluidic flow-patterning in conjunction with the DEAL approach, we have demonstrated the ability to integrate high density antibody barcode arrays within a microfluidic chip – the integrated blood barcode chip - that separates plasma from human whole blood for the simultaneous, sensitive detection of a large panel of proteins within minutes of blood collection. Herein, we report on the results of a clinical trial in which this platform was used to survey 35 cancer- and immune-related plasma proteins in over a hundred patients with glioblastoma multiforme (GBM), an aggressive malignancy of the brain. While none of these proteins is highly specific for GBM on its own, the systems biology approach of surveying a large number of proteins simultaneously yields a dramatic increase in disease-specificity, facilitating stratification of patients within minutes according to whether their tumors are responding to treatment. This contrasts sharply with imaging techniques, which require multiple scans over a period of weeks to months to ascertain whether the patient is responsive to treatment. The device therefore holds great promise in the rapid diagnosis and stratification of patients suffering from a whole host of other pathologies as well. Furthermore, we demonstrate an approach for flow patterning ultra-high density oligonucleotide and DEAL grid arrays that could, in principle, allow for the detection of the entire known plasma proteome within a single microfluidic channel. A particularly exciting extension of this technique is that it enables the assembly of multiplexed arrays of single cells that can be patterned in parallel to form dense 2-D and 3-D tissue engineered structures within minutes.
11:45 AM - KK2.2
Compartmented Device for the in-vitro Study of Neuronal Networks.
Thirukumaran Kanagasabapathi 1 , Michel Decre 1 , Ger Ramakers 2 Show Abstract
1 Healthcare Devices and Instrumentation, Philips Research Laboratories Europe, Eindhoven Netherlands, 2 Department of Developmental Psychology, University of Amsterdam, Amsterdam Netherlands
Following the paradigm of cell culture analogs , the development of in-vitro models forspecific neuronal pathways should provide insights into pathological neurodegenerative diseases and their treatment modalities that lack sufficient understanding. Further, using microsystem technologies to build and sustain such models offers easy accessibility and manipulation capabilities that are not available in traditional invivo studies. In this work, we present our progress in the development of such a system for in-vitro neuronal network cultures.
Microsystem technologies have recently been used to initiate in-vitro studies of separatedneuronal populations, either for chemical studies in both closed  and open  compartments, or for extracellular recordings of electrical activity in open compartments . Following the pioneering work by Taylor et al , we present a closed-compartment neurofluidic device with microchannels connecting two compartments, the whole system being integrated on a planar micro-electrode array (MEA). The two compartments are separated by 10-um-wide and 3-um high microchannels and this provides a physical isolation of neurons allowing only neurites to grow between the compartments. We discuss long term neuronal cell cultures in such devices, then demonstrate neurite growth through the microchannels connecting the compartments and finally present long-term recordings of the network activity over 21 Days-in-Vitro (DIV).
Results of electrophysiological recording from the compartmented cultures arepresented. Suppression of network activity within a compartment using neurotoxins andsubsequent recovery of network activity through successive wash cycles are presented todemonstrate that the recorded activity is indeed spontaneous network activity, and highlight the physical and fluidic separation between the compartments.Such compartmented devices for neuronal cultures should greatly contribute to the in vitro study of neuronal pathways, controled neuronal networks, and neuron-device interfaces.
 Folch, A. and M. Toner, Microengineering of cellular interactions. Annual Review ofBiomedical Engineering, 2000. 2: p. 227.
 Taylor, A.M., et al., Microfluidic multicompartment device for neuroscience research.Langmuir, 2003. 19(5): p. 1551-1556.
 Dworak, B.J., and B.C. Wheeler, Novel MEA platform with PDMS microtunnels enables the detection of action potential propagation from isolated axons in culture. Lab on a Chip, 2009. 9: p. 404-410.
 van Pelt, J., et al., Long-term characterization of firing dynamics of spontaneous bursts incultured neural networks. IEEE Transactions On Biomedical Engineering, 2004. 51(11): p.2051-2062.
12:00 PM - KK2.3
Controlling the Stretching and Alignment of Tethered DNA With Microfluidics for Organic Molecule Electronics.
Guihua Yu 1 , Eric S.G. Shaqfeh 1 2 , Zhenan Bao 1 Show Abstract
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Mechanical Engineering, Stanford University, Stanford, California, United States
The critical process in the creation of DNA-organic molecule-DNA (DoD) array structures for the study of single organic semiconducting molecule electronics is the tethering and stretching of DNA molecules. In this regard, we have made substantial progress in both theoretical and experimental studies of flow dynamics of tethered DNA molecules using microfluidics. Specifically, using DNA molecules tethered to a microfluidic channel and single molecule fluorescence microscopy, we have investigated the effect of shear rates on flow/extension behavior of tethered DNA molecules in the flow-gradient and the flow-vorticity plane. We have found that at high shear rates, DNA molecules experience “overstretching”, while at intermediate shear rates (up to ~80% extension), very interesting cyclic dynamics occur in the flow-gradient plane. Moreover, quantitative agreement in the cyclic frequency was obtained upon comparison between experiments and Brownian Dynamic simulations. Moreover, we demonstrate reproducible surface chemistry for tethering DNA at tunable surface density. Finally, the flow dynamics and its effect on various processing steps associated with using tethered DNA as scaffolds for molecule wires will be presented together with the progress for subsequent metallization of the DNA scaffolds that eventually leads to reliable and reproducible metal contacts for single molecule electronics.
12:15 PM - KK2.4
Microfluidic Arrays for Rapid Screening of Processing Parameters for Solution-processable Organic Semiconductors.
Christopher Bettinger 1 , Hector Beccerrill 1 , Cheng-Chung Lee 2 , Stephen Quake 2 , Zhenan Bao 1 Show Abstract
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Bioengineering, Stanford University, Stanford, California, United States
The electrical performance of devices based on organic semiconductors can vary significantly based on processing conditions. More specifically, solution-processable organic semiconductors, including both small molecules and polymers, are subject to a vast parameter space with respect to processing conditions. The solvent, solute concentration, evaporation conditions, and annealing temperature are all known to directly affect molecular packing, morphology, and crystallinity of organic semiconductor films, all of which produce a direct impact on the electrical performance of devices based on these structures. We hypothesized that a microfluidic-based platform could be utilized to rapidly screen the electrical properties of solution-processed organic semiconductors. In this work, we used soft-lithography to mold microfluidic devices composed of perfluoropolymer, which were designed to handle and mix small volumes of solution-processable organic semiconductors. These microfluidic devices were used to deposit arrays of regioregular poly(3-hexylthiophene) (P3HT) on silicon substrates treated with phenyltrimethoxysilane. The devices were designed to vary solute concentrations and binary solution composition across the microfluidic array. Substrates were then exposed to a thermal gradient, which varied the annealing temperature on the substrate spatially. The end result is a construct, which is able to create a two-dimensional array with varied solvent composition across one axis and varied thermal annealing temperatures across the orthogonal axis. In this study, we varied the relative compositions of the solvent from pure chlorobenzene to pure chloroform including intermediate compositions. We varied the thermal annealing temperature of the substrate from 118 to 220 degrees Celsius. Gold electrodes were deposited to complete the transistor structures and performance metrics of these devices were recorded. These high throughput arrays were able to screen a wide parameter space of processing conditions to identify trends in processing parameters. For example, annealing substrates at approximately 160 degrees Celsius produced optimal on-off ratios in P3HT across several solvent compositions. These constructs could also be used to optimize conditions with respect to device performance for future classes of solution-processable organic small molecule and polymeric semiconductors as well.
12:30 PM - KK2.5
A Microfluidic Platform for Characterization of DNA-DNA Interactions Based on Shear Force Spectroscopy.
Mehdi Javanmard 1 2 , Ronald Davis 1 Show Abstract
1 Stanford Genome Technology Center, Stanford University, Palo Alto, California, United States, 2 Electrical Engineering Department, Stanford University, Palo Alto, California, United States
Current methods used for detection of DNA hybridization involve the use of DNA microarrays which require overnight incubation times along with bulky and expensive fluorescent scanners. Here, we demonstrate electrical detection of DNA hybridization in an oligonucleotide functionalized microfluidic channel. We use micro-channels functionalized with DNA probes integrated with electrodes for measuring conductance across the channel. As beads conjugated with the target DNA passing through the channel are captured on the surface, we are able to electrically detect changes in resistance due to bead capture. Our assay can be completed in less than an hour using less than a microliter of reagent, and has the potential for extensive multiplexing. Such a device can be useful as a handheld platform in a clinical setting where one would need to rapidly genotype a small number of genes rapidly.We have also performed COMSOL simulations where we've calculated the drag force being applied to an attached particle for a given flow rate. We correlate these simulation results with experimental results where we measure the flow rate required to pull off the attached beads. Based on such, we are able calculate the strength of the bond between the probe and the target DNA and also the number of molecules holding down a bead. Based on this technique we can also determine the kinetic constants of the various interactions. We are able to distinguish between specific and nonspecific DNA-DNA interactions. With 40 base pair length DNAs we are not able to distinguish between single base pair mismatches, but this is expected. This is more like feasible with 20 base pair long DNAs. We intend to apply this technique to the detection of single nucleotide polymorphisms.
KK3: Crystallization and Phase Diagrams
Tuesday PM, April 06, 2010
Room 3014 (Moscone West)
2:30 PM - **KK3.1
The PhaseChip: Manipulating Phase Diagrams with Microfluidics.
Seth Fraden 1 Show Abstract
1 Physics, Brandeis University, Waltham, Massachusetts, United States
X-ray diffraction of protein crystals reveals protein structure, which is needed to advance fundamental understanding of protein function and for drug development. Currently the physical process of crystallization is the bottleneck in protein structure determination.The PhaseChip, is a microfluidic device that can precisely meter, mix, and store nanoliter volumes of sample, solvent, and other reagents. Thousands of nanoliter drops of different protein solutions can be stored in individual wells. Through the controlled kinetic manipulation of the solution chemical potential the process of nucleation and growth can be decoupled, which is crucial for optimizing protein crystallization.Movies illustrating the PhaseChip in action:http://www.elsie.brandeis.edu/
3:00 PM - KK3.2
Online Optical-SAXS Study of Microfluidic Processing of Model Surfactant Mixtures.
Hazel Martin 1 , Joao Cabral 1 Show Abstract
1 Chemical Engineering, Imperial College London, London United Kingdom
Concentrated surfactant solutions exhibit remarkably complex and potentially useful microstructural transitions under flow. We have investigated the non-equilibrium behaviour of model concentrated surfactant solutions under tailored microflow fields. The advent of microfluidic fabrication offers the opportunity to design and generate flow fields with unprecedented precision and flexibility, ranging from pure extension to pure rotation and including pure shear. We study systematically, for the first time, the influence of model flow fields on complex fluid microstructures with relevance to a variety of industrial applications such as manufacturing of personal care, food and coating products. We report the structure formation and disintegration of surfactant mixtures under flow probed by a combination of non-invasive techniques ranging from microscopy, spectroscopy and light & synchrotron X-ray scattering. Custom-made devices were developed for effective Xray studies. Model surfactant mixtures of CTAC and SDS were selected for their well-known lamellar equilibrium phase behaviour forming multilayered spherulites under shear. Its rheological properties have been associated with a swelling of lamellar phases. Polarised microscopy elucidated the effect of a microfluidic pulsating extensional flow gradient and show alignment and structural relaxation accompanied by a change in orientation and in number density of vesicles with time and flow rate. Using small angle x-ray scattering (SAXS), changes in the lamellar d-spacing and in orientation were observed and measured online in response to flow rate variations and a succession of abrupt extensional flow gradients. A focussed beam allowed a detailed spatio-temporal mapping of the processing route of this model surfactant mixture. References: Langmuir, 20, 10020 (2004); J. Micromech. Micromach. 14, 153 (2004); Polymer 46, 4230 (2005); Phys. Rev. E 72, 021801 (2005); Appl. Phys. Lett. 87, 081905 (2005); Lab Chip 6, 427 (2006); Soft Matter 4, 2360 - 2364, (2008); Adv Mater 2009 (submitted)
3:15 PM - KK3.3
Exploration of Temperature-concentration Phase Diagrams Using Microfluidics.
Seila Selimovic 1 , Frederic Gobeaux 1 , Seth Fraden 1 Show Abstract
1 Physics, Brandeis University, Waltham, Massachusetts, United States
We describe the PhaseChip, a microfluidic device for measuring the phase diagram of aqueous samples as a function of concentration and temperature. This double-layer (poly)dimethylsiloxane (PDMS) device contains a storage layer, in which hundreds of nanoliter sized aqueous droplets can be simultaneously formed and stored. A second layer, separated by a thin, water-permeable PDMS-membrane contains twelve reservoir channels filled with different salt solutions. When there is a difference between the concentrations of salt in the reservoir solutions and the aqueous droplets, water migrates across the membrane and causes the droplets to reversibly shrink or expand. As a consequence, the concentration of all solutes inside the droplets changes. Our experimental setup also incorporates a temperature gradient stage – a second crucial thermodynamic parameter that affects the phase stability. The PDMS device is positioned such that the direction of the temperature gradient is perpendicular to the concentration gradient. In effect, the PhaseChip now displays a two-dimensional phase diagram of the polymer or protein in question, with each position on the chip corresponding to a particular value of concentration and temperature. Hence, the PhaseChip enables us to study a wider concentration and temperature dependent phase space of protein and polymer than previously, and conduct hundreds of crystallization screens simultaneously, while conserving the amount of solute needed. Robust operation of the PhaseChip is demonstrated on four model systems: liquid-liquid phase separation in a polyethylene glycol (PEG) – salt mixture and in bovine eye-lens protein (γB crystallin), and crystallization experiments on Lysozyme from chicken egg white and N-acyl-L-homoserine lactonase AiiB(S35E) from Agrobacterium tumefaciens.
3:30 PM - KK3.4
Microfluidic Platforms for Characterization of Membrane Protein Crystallization in Lipidic Mesophases.
Daria Khvostichenko 1 , Sarah Perry 1 , Sudipto Guha 1 , Johnathan J. Ng 1 , Charles Zukoski 1 , Paul J. Kenis 1 Show Abstract
1 Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Transmembrane proteins control a variety of processes in the cell, such as signal recognition, transmembrane transport, immune response, and account for over 60% of all human drug targets. Mechanistic understanding of their functionality ultimately relies on three-dimensional structures typically obtained from X-ray diffraction data. However, growth of X-ray quality membrane protein crystals is notoriously difficult due to their intrinsic amphiphilicity and poor stability after removal from native membrane environment. Pioneered by Landau and Rosenbusch, crystallization from lipidic mesophases overcomes this problem by reconstituting the protein into lipidic bilayer structures spontaneously formed in mixtures of certain surfactants with water. Among recent successes of the method are crystal structures of human β2-adrenergic receptor and A2A receptor. The mechanism of crystallization in meso is poorly understood, but it is believed that transformations of the lipidic mesophase microstructure play a crucial role. Despite the advantages of membrane protein crystallization from lipidic mesophases, the method has several limitations that hinder its acceptance as the method of choice. Although only several nanoliters of sample may be required for growth of protein crystals, initial preparations typically require µL quantities due to difficulties in mixing and dispensing of highly viscous lipidic mesophases. Harvesting protein crystals from the mesophase can also be challenging. We developed several microfluidic platforms for studies of in meso crystallization that obviate macroscale preparation of the protein solution/lipid mixture prior to crystallization trials. Sample mixing and screening of in meso crystallization conditions are performed on-chip using < 10 nL of protein solution per trial. Presently, we are pursuing an X-ray transparent version of this platform in order to enable on-chip X-ray diffraction studies and to eliminate post-growth manipulation of fragile crystals. These platforms can also be used for mechanistic studies and characterization of in meso crystallization systems, such as rapid screening of phase behavior and microstructure of lipidic mixtures on-chip by small-angle X-ray scattering. In addition to studies of equilibrium properties, microfluidic capabilities to create well-controlled interfaces between different phases are exploited to investigate gradient-driven transport of membrane proteins in the mesophase, which is of vital importance for crystal growth. Results of such studies may suggest strategies for optimization of crystallization conditions and thus improve success rate of membrane protein crystallization trials.
3:45 PM - KK3.5
Enhancement of On-chip Bioassay Efficiency With Electrothermal Effect.
Sheng Chao 1 Show Abstract
1 , National Taiwan University , Taipei Taiwan
The working principle of immunoassays is based on the specific binding reaction of an analyte-ligand protein pair in physiological environments. However, for a diffusion-limited protein, the diffusion boundary layer of the analyte on the reaction surface of a biosensor would hinder the binding reaction from association and dissociation. The formation of such association and dissociation boundary layers thus limits the response-time and the overall performance of a biosensor. In this work we have performed a full time scale finite element simulation on the binding reaction kinetics of two commonly used proteins, CRP and IgG. By applying a non-uniform ac electric field to the flow micro-channel of the biosensor, the electrothermal force can be generated and induce a pair of vortices to stir the flow field. With the aid of the vortices and a suitable choice of the location of the biosensor, the fluids flowing over the reacting surface can be accelerated to depress efficiently the growth of the diffusion boundary layer on the reaction surface, and enhance the association or dissociation of analyte-ligand complex. The interference patterns of the flow field due to the existence of the sensor at different locations of the micro-channel could cause different degrees of enhancement to the association and the dissociation. By changing the location of the sensor the largest enhancement is found at the position near the negative electrode. For the configuration of the micro-channel we studied, the initial slope of the curve of the analyte-ligand complex versus time can be raised up to 5.17 for CRP and 1.93 for IgG in association, and 3.74 for CRP and 1.28 for IgG in dissociation, respectively, under the applied ac field 15 Vrms and operating frequency 100 kHz. An improved design incorporating a pair of electrodes and a neck region near the reaction surface is demonstrated. The sensor is fixed to locate at the middle of the bottom side. With the existence of the stirring flow field, the association rate of the 30 μm-neck is 2.73 times faster than that of the original channel with no neck.
Tuesday PM, April 06, 2010
Room 3014 (Moscone West)
4:30 PM - **KK4.1
From Dissolution of CO2 Bubbles to Chemically Mediated Formation of Particulate Materials.
Eugenia Kumacheva 1 3 2 , Jai Il Park 1 , Zhihong Nie 1 , Alexander Kumachev 1 , Ethan Tumarkin 1 , Bernard Binks 4 , Howard Stone 5 Show Abstract
1 Department of Chemistry, University of Toronto, Toronto, Ontario, Canada, 3 The Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada, 2 Department of Chemical Engineering & Applied Chemistry, University of Toronto, Toronto, Ontario, Canada, 4 Department of Chemistry, University of Hull, Hull United Kingdom, 5 Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, United States
Bubbles generated by the microfluidic means are typically produced from gases with a limited solubility in water. A fundamental study of the formation of bubbles from gases that dissolve in and react with the continuous phase has yet to be conducted. Such gases, e.g., NH3 or CO2 have direct environmental impact owing to their high solubility in water and are also used in heterogeneous gas-liquid chemical reactions. We present the results of an experimental study of the microfluidic formation of bubbles of CO2. The system shows a strong 'feedback' behaviour in which the dissolution of CO2 bubbles leads to the drop in hydrodynamic pressure in the microchannels and results in the formation of larger CO2 bubbles. We show the effect of environmental conditions on the initiad and stabilized bubble size.We show three practical applications of the controllable and robust CO2 shrinkage which leads to the local increase in acidity of the medium: (a) the generation of small (<10 μm) bubbles, (b) chemically mediated production of bubbles coated with colloidal shells and (iii) the formation of small, stable bubbles coated with a biopolymer shell.
5:00 PM - **KK4.2
Bubbling Using Different Devices.
Mohan Edirisinghe 1 , Eleanor Stride 1 Show Abstract
1 , University College London, London United Kingdom
The conventional and convenient method for preparing stable bubbles in a liquid or liquid suspension is via sonication. However, the control over the size and size-distribution of the bubbles provided by this method is inadequate, especially for biomedical applications such as imaging and targeted therapies. With these in mind we have developed new bubbling techniques to address these limitations. The first is the preparation of bubbles using electrohydrodynamics where a liquid/suspension is made to co-flow with a gas under the influence of an electrical field. In this way bubble populations of size <10µm with a polydispersivity index of <10% can be prepared at commercially viable rates. The size of bubbles obtained can be precisely controlled via the three main processing parameters: – the applied voltage and liquid and gas flow rates. The method also facilitates the preparation of coated bubbles with multiple layers which have many potential applications e.g. for drug delivery. The gas core can also be substituted by a volatile liquid to prepare well characterised hollow capsules, with or without a monopore. For the second method, we have developed microfluidic T-junctions to prepare bubbles with a polydispersivity index of <1%. These bubbles can be incorporated within polymer gels to prepare porous films and can also be “armoured” by coating them with nanoparticles in order to enhance their stability and the non-linear character of their response to ultrasound which has benefits for medical imaging. In the third, hybrid technique, the size and population of the bubbles obtained from the T-junction can also be dramatically changed by imposing an electric field at the T-junction output. The relative advantages of the different methods with respect to sonication and each other will be discussed.
5:30 PM - KK4.3
Microfluidic Fabrication of Stable Nanoparticle-shelled Microbubbles.
Myung Han Lee 1 , Varesh Prasad 2 , Daeyeon Lee 1 Show Abstract
1 Chemical and Biomolecular Eng, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Monodisperse and stable microbubbles could find use in medical applications such as ultrasound contrast agents and targeted drug delivery vehicles as well as in food and cosmetics industry for encapsulation of fragrances. It is, however, not trivial to make gas bubbles with high uniformity in size and properties, and store them without significant changes in size for an extended period of time. Bubbles shrink and eventually dissolve due to the Laplace pressure across the air-water interface. Bubbles also undergo coarsening through Oswald ripening process making it very difficult to retain size uniformity. Here, we introduce a microfluidic approach to generate monodisperse microbubbles stabilized by nanoparticle shells. A monodisperse air-in-oil-in-water (A/O/W) compound bubble, generated by a glass capillary microfluidic device, is used as a template for the generation of nanoparticle-shelled microbubbles. The oil phase comprises a volatile organic solvent in which hydrophobic silica nanoparticles are suspended. Upon the evaporation of the organic solvent, the nanoparticles in the oil layer form a stiff shell at air-water interface. The elastic response of the nanoparticle shell arrests the dissolution of gaseous core into the continuous phase. Nanoparticle-shelled bubbles are stable and retain their size uniformity for at least several months. Based on our approach of using A/O/W compound bubbles as templates, we can also generated microbubbles stabilized by composite shells that are composed of mixtures of hydrophobic molecules and nanoparticle with unique properties. We demonstrate the versatility of approach by creating fluorescent and magnetic microbubbles.
5:45 PM - KK4.4
Monodispersed Ceramic Capsules from Double Emulsion Drops.
Carlos Martinez 1 , Congwang Ye 1 , Paolo Colombo 2 Show Abstract
1 School of Materials Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Dipartimento di Ingegneria Meccanica - Settore Materiali, Università di Padova, Padova Italy
Double emulsions (water/oil/water) are suspensions consisting of small droplets dispersed within larger drops, which are themselves dispersed in another fluid. They are used in various industries (e.g. cosmetics) to encapsulate compounds and control their release. However, their use in advanced applications such as bio-encapsulation, and advanced ceramic fabrication has been limited since their traditional fabrication via a two-step emulsification offers little control over their structure. It is not until recently that microfluidic techniques have opened the possibilities of generating monodispersed double emulsion drops that can be tailored for advanced applications. In this talk, I’ll highlight recent efforts in my group to develop a robust technique to fabricate ceramic core-shell structures from monodispersed single and double emulsions generated using microcapillary microfluidic devices. In our system the middle fluid (oil phase) which is the shell of the capsules, is composed of a poly (methylsilsesquioxane) resin (the ceramic precursor), dissolved in a mixture of 1 cSt polydimethylsiloxane (PDMS) oil and Zr-acetylacetonate (crosslinker). The inner fluid is an aqueous solution of Zr-acetylacetonate and the outer fluid contains a mixture of water and glycerol. Monodispersed crosslinked capsules with sizes ranging from 30 microns to 200 microns and different shell thicknesses were generated by varying the fluid flow rates and the device geometry. These are then turned into oxycarbide glass capsules by drying, and then pyrolyzing at 1100 °C. Capsules with porous shells and with multiple materials such as iron and alumina were also fabricated by changing the composition of the middle and inner fluids. Finally, we’ll show how to tailor the capsule’s porosity by osmotically regulating the flow of water in and out of the double emulsions.
Carlos J. Martinez Purdue University
Sonia Grego RTI International
Alberto Fernandez-Nieves Georgia Institute of Technology
Joao Cabral Imperial College London
KK5: Electric Field-Controlled Flow
Wednesday AM, April 07, 2010
Room 3014 (Moscone West)
9:15 AM - **KK5.1
Experimental Characterization of the Whipping Instability of Charged Microjets in Liquid Baths.
Gillaume Riboux 2 , Venkata Gundabala 3 , Alvaro Marin 2 , Antonio Barrero 2 , Alberto Fernandez-Nieves 3 , Ignacio Gonzalez-Loscertales 1 Show Abstract
2 , Universidad de Sevilla, Sevilla Spain, 3 , Georgia Institute of Technology, Atlanta, Georgia, United States, 1 , Universidad de Málaga, Málaga Spain
Capillary liquid flows have shown their ability to generate micro and nano-structures which can be used to synthesize material in the micro or nanometric size range. For instance, electrified capillary liquid jets issued from a Taylor are broadly used to spin micro and nanofibers when the liquid consists of a polymer solution or melt, a process termed electrospinning. In this process, the electrified capillary jet may develop a nonaxisymmetric instability, usually referred to as whipping instability, which very efficiently transforms electric energy into stretching energy, thus leading to the formation of extremely thin polymer fibers. Even though non axysimmetric instabilities of electrified jets were first investigated some decades ago, the existing theoretical models provide a qualitative understanding of the phenomenon but none of them is accurate enough when compared with experimental results. This whipping instability usually manifests itself as fast and violent lateral motion of the charged jet, which makes it difficult its characterization in the laboratory. However, this instability also develops when electrospinning is performed within a liquid bath instead of air. Although it is essentially the same phenomenon, the frequency of the whipping oscillations is much slower in the former case than in the latter, thus allowing detailed experimental characterization of the whipping instability. Furthermore, since the outer fluid is a liquid, its density and viscosity may now be used to influence the dynamics of the electrified capillary jet. In this work we present and rationalize the experimental data collecting the influence of the main parameters on the whipping characteristics of the electrified jet (frequency, amplitude, etc.). Also, we shall comment on the influence of the external liquid on the electro-atomization process.
9:45 AM - **KK5.2
Block Copolymer Self-assembly Under Cylindrical Confinement at the Nanoscale.
Greg Rutledge 1 , Minglin Ma 1 , Edwin Thomas 2 , Baohui Li 4 , An-Chang Shi 3 Show Abstract
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States, 2 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 4 Physics, Nankai University, Tianjin China, 3 Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada
Fibers with long range ordered internal structures have applications in various areas such as photonic band gap materials, optical waveguides, sensors and sustained drug release. Until recently, such fibers were formed by melt extrusion or solid state drawing from a macroscopic perform, and were typically limited to diameters >10 μm, with internal features > 1μm. Electrohydrodynamic processing of fibers, also known as electrospinning, provides an alternative method to produce continuous fibers with diameters below 1 μm. Co-axial electrospinning of fibers with a block copolymer as the core component of a core-shell fiber morphology enables the formation of fibers with diameters and feature sizes 2-3 orders of magnitude smaller than those made by conventional methods. The “top-down” fabrication of the core-shell morphology, with submicron dimensions, combined with the “bottom-up” self-assembly of cylindrically confined ordered block copolymer phases, leads to novel morphologies and metastable structures. Examples of these from the confined self-assembly of lamellar, cylindrical, spherical and gyroid-forming phases are presented, and compared with theoretical expectations. Modeling suggests that such systems exhibit a rich diversity of metastable morphologies under cylindrical confinment, depending upon the degree of confinement, commensuration of the confining geometry with the intrinsic period of the ordered block copolymer phase, and the relative preference of one block or the other for interaction with the confining material. The experimental observations confirm a number of these metastable morphologies. The co-axial electrospinning technique is sufficiently robust to explore a broad range of interactions and degrees of confinement.
10:15 AM - KK5.3
Electric Field Control of Flow in Nanoscale Thin Wetting Films.
Sejong Kim 1 , Jairus Kleinert 1 , Orlin Velev 1 Show Abstract
1 Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States
We report a novel electric-field-controlled nanoscale flow system based on patterned wetting films on hydrophilic surfaces. Water films formed spontaneously on mica substrates under saturation humidity conditions. Measurements of interference patterns and the intensity of fluorescent dye in the films indicated that the films were less than 100 nm thick. Flow in the films parallel to the mica substrates was induced by applying a DC electric field across the films. The direction and speed of the flow were controllable by modulating the field polarity and intensity. Flow was observed using a fluorescent marker and analyzed with electroosmotic theory. The electroosmotic mobility was lower than that predicted by the Helmholtz-Smoluchowski equation and nonlinear, a consequence of the film thickness approaching the Debye length of the counterionic layer at the mica surface. To direct the film along defined paths, two-dimensional “virtual wall” channels were created by selectively hydrophobizing the substrate by microcontact printing silane patches. This system was used to visualize flows of polymer brush monolayers with atomic force microscopy. Control of such molecular flows in combination with electric field techniques for orienting molecules may permit fabrication of surfaces with coatings ordered at the nanoscale. This nanofluidics methodology will be further developed with the goal of constructing devices for single biomolecule transport and manipulation.
10:30 AM - KK5.4
Electro-Coflow: A Novel Approach to Coupling Electric and Hydrodynamic Forces for Controlled Droplet Generation.
Venkata Gundabala 1 , Alberto Fernandez-Nieves 1 Show Abstract
1 School of Physics, Georgia Institute of Technology, Atlanta, Georgia, United States
Liquid-liquid emulsion droplets in the micron and sub-micron size range find applications in several fields such as cosmetics, drug delivery, and food industry. Microfluidics offers a promising route to produce these droplets by decoupling the droplet size from its composition. Here we propose a novel method to produce emulsion droplets in the sub-micron size range in a microfluidic device that couples electric and hydrodynamic forces. Electric fields are applied to a conducting liquid coflowing with an outer insulating liquid in a glass-based coflow geometry. We investigate the drop formation mechanism as a function of operating parameters such as the applied electric field strength, flow rates of the inner and outer liquids, and device geometry. Two modes of operation for the stable generation of emulsion droplets are observed: Cone-Jet mode and Whipping mode. Both the modes operate in a steady-state manner over long periods of time, allowing continuous generation of monodisperse emulsion droplets. For a given conductivity of the inner liquid, the smallest possible droplet diameter is obtained for small inner flow rates, high outer flow rates and high applied voltages. Measured currents from the experiments indicate a strong dependence on applied voltage and a weak dependence on inner flow rate indicating the charge transport mechanism to be predominantly conductive. We envisage this observation to be a consequence of the small size ratio of capillary tip to the jet diameter which prevents the establishment of convective regime. This result is in stark contrast with what is expected in an electrospray where the outer medium is air rather than a coflowing insulating liquid.
10:45 AM - KK5.5
Low-frequency AC Electro-flow-focusing Microfluidic Emulsifications.
Peng He 1 , Haejune Kim 1 , Dawei Luo 1 , Manuel Marquez 2 , Zhengdong Cheng 1 Show Abstract
1 Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas, United States, 2 , Ynano LLC, Midlothian, Virginia, United States
Microfluidic emulsification can be significantly optimized if the droplet size could be tailored at will. Integrating electric field into flow-focusing devices has shown a great potential to control the breaking, coalescence, and sorting of droplets. However, only a few studies have been conducted with embedded AC electric field, mostly of very high frequencies, and neither the combination of electric field and flow-focusing for emulsification nor the use of a low-frequency AC electric field has been thoroughly exploited. We conducted the low-frequency AC electro-flow-focusing emulsification in microfluidic channels. Because of the relaxation oscillation of the flow through the Taylor cone, in spite that the influx flow rates of the aqueous and oil phases were constant, we observed a droplet size variation that did not simply follow the electric field variation. Particularly, a power-law droplet size distribution was obtained at the voltage ramping-up region. This emulsification process was modeled in analog to the charge accumulation and release in an RC electric circuit.
KK6: Particle Assembly and Nanofluidics
Wednesday PM, April 07, 2010
Room 3014 (Moscone West)
11:30 AM - **KK6.1
Opto-electric Manipulation of Droplets and Colloids for Material Assembly.
Steve Wereley 1 2 , Stuart Williams 1 2 , Aloke Kumar 1 2 , Oswald Chuang 1 2 , Jae-Sung Kwon 1 2 , Cara Smith 1 2 Show Abstract
1 Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States
This talk will discuss several emerging methods for manipulating and assembling novel materials based on several opto-electric droplets and colloid manipulation techniques. We manipulate droplets using a novel open optoelectrowetting (O-OEW) technique which features dynamic droplet maneuverability and great extensibility due to light-induced virtual electrodes and an open configuration. The O-OEW device comprises coplanar interdigitated electrodes, a photoconductor, and an insulator on a single substrate. Under illumination the impedance of the photoconductor decreases, creating an electrowetting effect due to a high voltage drop in the insulator. Without illumination the impedance of the photoconductor increases, shifting the voltage drop back to the photoconductor layer and shutting off the electrowetting. The illumination induces a localized hydrophilic region on an overall hydrophobic surface, causing an imbalance of surface tension forces and the subsequent liquid droplet movement. By selectively illuminating the platform surface, basic droplet operations are implemented, such as translation, merging, and simultaneous multi-droplet control. Immersing the liquid droplets in oil enhances the movements and reduces evaporation. A second opto-electric technique, called Rapid Electrokinetic Patterning (REP), rapidly and continuously accumulates colloids on an electrode surface, assembling crystalline layers of thousands of suspended colloids in seconds. We demonstrate this assembly method for particles ranging from 50 nm to 3 μm. Electrothermal hydrodynamics produce a microfluidic vortex that carries particles in suspension towards its center where they are trapped by low-frequency AC electrokinetic forces. We characterize the rate of particle aggregation as a function of the applied AC voltage and hence characterize trapping kinetics of this technique. We show that inter-particle distance varies with frequency and we explain this in the light of available theory. Together these two techniques are capable of constructing truly novel materials.
12:00 PM - KK6.2
Experimental and Theoretical Comparison of Aspect-ratio-dependent Diffusion of CdSe Nanocrystals Through Nanochannels.
Louis Tribby 1 , Cornelius Ivory 2 , Frank van Swol 3 , Sang Han 1 Show Abstract
1 Chemical & Nuclear Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 2 Chemical Engineering and Bioengineering, Washington State University, Pullman, Washington, United States, 3 , Sandia National Laboratories, Albuquerque, New Mexico, United States
The use of nanofluidic devices as a means of separating biomolecules, nanoparticles, and other small species is of fundamental importance. Experimentally obtained transport properties can be compared to theory and computer simulations to further elucidate our understanding of their transport properties at the nanoscale. In particular, we have evaluated toluene suspensions of CdSe nanocrystals (NCs) to determine the effect of their aspect ratio on the diffusion constant and eventual equilibrium concentration in nanochannels (100 nm w x 400 nm d). To quantitatively monitor NC diffusion, we measure spectrally resolved photoluminescence (PL) from these NCs as a function of time and distance from the nanochannel inlet, using laser scanning confocal microscopy. The PL intensity is compared to a diffusion model that allows for NC-wall adsorption. The comparison reveals that the hindered NC diffusion constant is approximately two orders of magnitude lower than that observed in microchannels and that the NC-wall adsorption is not negligible. The NC equilibrium concentration, approximated by the NC concentration near the nanochannel inlet, also reveals aspect ratio dependence that compares well with a theory that accounts for physical interactions of NCs with channel geometry. We will further discuss the electrokinetic transport of NCs in aqueous solutions through nanochannels.
12:15 PM - KK6.3
Nanofluidic Behavior in a Functionalized Nanoporous Silica Gel.
Yu Qiao 1 , Ricardo Franco 2 , Xiaoyue Li 2 , Aijie Han 2 Show Abstract
1 Structural Engineering, University of California-San Diego, La Jolla, California, United States, 2 Chemistry, University of Texas-Pan American, Edinburg, Texas, United States
As liquid molecules are confined in a nanometer-sized channel, classic continuum fluid mechanics is no longer relevant, and a number of interesting phenomena have been discovered. A pressure-induced-infiltration (PII) technique is developed so as to investigate nanofluidic behavior on large length and time scales in this report. As a hydrophobic nanoporous material is immersed in a nonwetting liquid, an external pressure must be applied to overcome the capillary effect to force the liquid molecules into the energetically unfavorable nanopores. On the basis of the measurement of infiltration pressure and infiltration volume, the effective solid-liquid interfacial tension can be estimated. The infiltration pressure increases with the prolonged organosiliane treatment time, whereas the infiltration volume is not dependent on the surface coverage. As an electrolyte is added, however, the variation in infiltration pressure is negligible over a broad. By using this technique, the motion of pressurized liquid can be conveniently examined over a broad temperature range. These phenomena can be attributed to the confinement effect of pore walls in the nanoenvironment.
12:30 PM - KK6.4
Nanofluidic Systems: In situ Investigation of Mass Melting, Flowing, and Evaporation at Attogram Level from Individual Nanotubes.
Lixin Dong 1 , Xinyong Tao 2 , Li Zhang 3 , Xiaobin Zhang 4 , Bradley Nelson 3 Show Abstract
1 , Michigan State University, East Lansing, Michigan, United States, 2 , Zhejiang University of Technology, Hangzhou China, 3 , ETH Zurich, Zurich Switzerland, 4 , Zhejiang University, Hangzhou China
Nanofluidic systems are of increasing interest due to their potential applications in mass and energy transport by controlled melting and flowing, nanostructuring by deposition and welding, and sensing and actuation by using the change of mass positions and fluidic pressures. Controlled melting, evaporation, and flowing of copper and tin intra-/inter-nanotube shells are investigated experimentally using in situ manipulation tools. Electric current and field driven heating, diffusion, polarization , and electromigration under low bias voltages are realized and the efficiency is compared. Based on the spot welding using single-crystalline copper-filled carbon nanotubes (CNTs) using nanorobotic manipulation inside a transmission electron microscope (TEM), self-soldering of CNTs onto electrodes using the encapsulated copper is developed. Controlled melting and flowing of copper inside nanotube shells are realized by applying bias voltages. With the continuing development of bottom-up nanotechnology fabrication processes, self-soldering can play a role for the interconnection of nano building blocks for the assembly of nanoelectronics and nanoelectromechanical systems (NEMS). Controlled melting, evaporation and flowing of copper and tin within and between nanotube shells are investigated experimentally. These CNT fluidic junctions can serve as basic elements for more complex nanofluidic systems, and can also provide a structure for testing theories of fluid flow at the nanoscale. A comparison shows that the mass loss for the cap-to-wall architecture is much smaller than that for the wall-to-cap junction. Controlled copper evaporation at attogram level from individual CNT vessels is investigated in different modes induced by electric current, Joule heating, charge, and ionization, which can serve as nanoscale physical vapor deposition (PVD) devices. Experiments and analyses show that the most effective method for evaporation is by positively ionizing the encapsulated copper; therefore, an electrostatic field can be used to guide the flow.
KK7: Flow Droplets and Diffusion
Wednesday PM, April 07, 2010
Room 3014 (Moscone West)
2:30 PM - **KK7.1
David Weitz 1 Show Abstract
1 , Harvard University, Boston, Massachusetts, United States
Microfluidic devices are ideal structures for the production of highly monodisperse drops of one fluid in a second, carrier fluid. These drops are of great value as templates for creating structures that can be used for encapsulation. The drops can also be used as micro-reactors for ultra high throughput bio-reactions. This talk will summarize some of the recent uses explored in our lab.
3:00 PM - **KK7.2
Electrospray of a Very Viscous Liquid in a Dielectric Liquid Bath.
Francisco Higuera 1 Show Abstract
1 , UPM, Madrid Spain
Order of magnitude estimates and numerical computations are used to analyze a jet of a very viscous liquid of finite electrical conductivity that is injected at a constant flow rate in an immiscible dielectric liquid under the action of an electric field. The conditions under which the injected liquid can form an elongated meniscus with a thin jet emanating from its apex (a cone-jet) are investigated by computing the flow, the electric field, and the transport of electric charge in the meniscus and a leading region of the jet. The boundaries of the domain of operation of the cone-jet mode are discussed. The current transfer region determining the electric current carried by the jet is analyzed taking into account the viscous drag of the dielectric liquid surrounding the jet. Conditions under which the electric current/flow rate characteristic follows a square root law or departs from it are discussed.
3:30 PM - KK7.3
Conformational Hysteresis of a Dingle DNA Molecule in Linear 3D Flows: A Brownian Dynamics Study.
Shikha Somani 1 , Eric Shaqfeh 1 2 Show Abstract
1 Chemical Engineering, Stanford, Stanford, California, United States, 2 Mechanical Engineering, Stanford, Stanford, California, United States
Understanding the dynamics of biopolymers in complex flows is critical for the successful design of lab-on-a-chip devices. Controlled flow in microfluidic channels can be used to trap and extend single molecules of DNA for applications like detection of target sequences along the DNA backbone, for single molecule kinetic and binding dynamic studies as well as for single molecule sorting. Such control entails a thorough understanding of the coil to stretch transition and conformational hysteresis of a single molecule as a function of flow strength, flow type and solvent quality. To study this system, we perform Brownian dynamics simulations using a polymer dumbbell model in linear 3D flows, rigorously including effect of hydrodynamic interactions by conformation dependent drag. It is observed that an increase in vorticity of the flow increases the conformational fluctuations of the polymer, leading to a decrease in the width of coil-stretch hysteresis. For all elongational-dominated 3D flows, the increase in conformational fluctuations is explained in terms of an effective conformational diffusivity, which can be evaluated using convective dispersion analysis. This has tremendous implications in the design and operating parameters of a microfluidic device since hysteresis cycles may directly influence bulk-solution stresses and the development of stress-strain relations for dilute polymer flows.
3:45 PM - KK7.4
Accelerated Determination of Diffusion Coefficients on a Chip.
Kirn Cramer 1 , Sachin Jambovane 1 , Jong Wook Hong 1 Show Abstract
1 Materials Research and Education Center, Department of Mechanical Engineering, Auburn University, Auburn, Alabama, United States
Diffusion plays a paramount role in many scientific areas including materials engineering, pharmaceutical, biotechnology and fuel cells to name a few. In the diffusion field, the term diffusion coefficient, D is usually used as the parameter for quantifying the diffusion phenomena. At present, diaphragm cell or chromatography or optical based methods are commonly employed to find out the values of diffusion coefficients. Though they use bulky equipment and require time consuming experimental setup, hence become major disadvantages. In the past, to overcome these disadvantages, many research groups have tried to reduce the size of the instrument alongwith fast performance, by using microfluidic based devices. However, they utilized very long dispersion channels within the chip just replicating the big instrument on the smaller scale. Herewith, we present a microfluidic device for the accelerated determination of diffusion coefficients. The chip consists of three separate but equal volume sized diffusion chambers. Therefore the three simultaneous diffusion tests could be performed to quantify the value of the average diffusion coefficients. In conclusion, this study will address the problem of achieving quick quantification of diffusion coefficients by using integrated microfluidic chip. The major advantages of the device include smaller size, shorter testing time with flexibility for fast experimental setup.
KK8: Synthesis: Particles and Membranes
Wednesday PM, April 07, 2010
Room 3014 (Moscone West)
4:30 PM - **KK8.1
Generating Colloids and Colloidal Assemblies With Microfluidic Technology.
Patrick Tabeling 1 Show Abstract
1 Microfluidics, ESPCI, Paris France
With microfluidic technology, one currently generates monodisperse droplets and bubbles in the range 10-100 micrometers. This range of size is relevant for a number of applications in chemistry, biotechnology, crystallisation, material sciences and cosmetics. Here we show that microfluidic technology can also be dedicated to the generation of monodisperse colloidal droplets. More specifically, we succeeded, at ESPCI, to generate, under high throughput conditions, monodisperse droplets, simple, multiple, photocured or not, including liquid or gaseous phases, whose size lies between 1 and 3 microns. This domain corresponds to the upper range of sizes of the colloidal world. The colloidal synthesis was performed by combining, on the same chip, a nanofluidic and a microfluidic section. In the course of this work, we observed a novel phenomenon, we called "capillary focusing", which contributes to ensure excellent control of the synthesis process. The colloidal droplets could be assembled in a few tens of seconds directly on the chip into ordered crystals that diffract visible light, suggesting novel methodologies for the synthesis of photonic materials. Applications to the domain of vectorization are illustrated by phagocytose experiments.
5:00 PM - **KK8.2
Droplet Based Microfluidics for Synthesis of Mesoporous Silica Microspheres.
Dimiter Petsev 1 , Nick Carroll 1 , Svitlana Pylypenko 1 , Paul Maksymiuk 1 , Amber Ortiz 1 , Bryan Yanemoto 1 , Ciana Lopez 1 , Plamen Atanassov 1 , David Weitz 2 Show Abstract
1 Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 2 Engineering and Applied Science, Harvard University, Cambridge, Massachusetts, United States
Particles with well-defined pore morphology are essential for many areas of modern technology. Potential applications include catalysis and electro-catalysis, chromatography, drug delivery, etc. Precise control over the pore size and shape is crucial for the successful performance of the particles. It allows optimizing the fluid transport in a catalyst, determines the molecular release of solute by a drug delivering vehicle, or defines the size selectivity in chromatography. Using microfluidics provides a better control over the particle size and monodispersity. We also show that templating specially designed oil/water/surfactants mixtures may lead to hierarchically (bidisperse) porous structures. These structures can be templated into silica (or other metal oxides) microparticles. Tuning the solution phase state by selecting the surfactants composition and concentration allows obtaining a system where microemulsion droplets (~40 nm) coexist with much smaller micelles (~5 nm). The presence of these species was proven by a dynamic light scattering experiment. The microemulsion droplet and micellar dimensions determine the two types of pores in the particles. Ordering monodisperse particles in 2D and 3D structure provides a third level of porosity associated with the dimension of the microspheres. The obtained porous structures can be directly used as supports in heterogeneous catalysis or can be infused with a pharmaceutical compound for targeted drug delivery. Templating such structures with other precursors offer the possibility to significantly expand the materials of choice. An example is the templating of the porous silica with sucrose solution which can be carbonized. After removing the silica scaffold we can obtain a “lost wax” carbon replica of the original inorganic particle. The procedure has been further developed to fabricate carbon/platinum microparticles for fuel cell catalysis.
5:30 PM - KK8.3
Membrane Formation by Adhesion of Amphiphilic Polymer Layers.
Ho Cheung (Anderson) Shum 1 , Jerome Bibette 3 , David Weitz 1 2 Show Abstract
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 3 Laboratoire Colloïdes et Matériaux Divisés, Ecole Supérieure de Physique et Chimie Industrielle, Paris France, 2 Department of Physics, Harvard University, Cambridge, Massachusetts, United States
Amphiphilic polymer molecules attract and form precipitates in a poor solvent. We use microfluidic techniques to confine amphiphilic polymer molecules at interfaces; by reducing the quality of the solvent for the polymer, we show that two neighboring interfaces become adhesive and form amorphous membranes. By measuring contact angles at the junction of the interfaces, we deduce the energy of adhesion and propose a physical explanation behind the membrane formation process. The membranes have a similar structure as lipid bilayers. Thus, understanding of our system sheds light on the self-assembly of lipids and formation of cell membranes. We also employ the technique to form vesicles with single and multiple compartments, as well as vesicle gels. These novel structures offer a robust and promising class of materials for encapsulating actives for applications in cosmetics, food and beverages, as well as biomedicals.
KK9: Poster Session
Thursday AM, April 08, 2010
Salon Level (Marriott)
9:00 PM - KK9.1
On-chip Aptamer-based Sandwich Assay for Thrombin Detection Employing Magnetic Beads and Quantum Dots.
Yolanda Tennico 1 2 , Daniela Hutanu 2 , Cheryl Moody Bartel 2 , Vincent Remcho 1 Show Abstract
1 , Oregon State University, Corvallis, Oregon, United States, 2 , Life Technologies Corporation, Eugene, Oregon, United States
We report here the development of an on-chip aptamer-based fluorescence assay for protein detection and quantification based on sandwich ELISA principles. Thrombin was selected as the model analyte to validate the assay design, where the assay involved the sandwich between two DNA thrombin aptamers recognizing two different epitopes of the protein. Aptamer-functionalized magnetic beads were used to capture the target analyte. A second aptamer, functionalized with quantum dots, was employed for on-chip detection. During the process, binding of thrombin between the two aptamers via the sandwich assay was monitored by fluorescence microscopy. Disposable microfluidic devices, fabricated by thermal embossing and a surface-modification assisted bonding technique, were used as the platform to perform the sandwich assay that enabled rapid thrombin detection with high sensitivity and specificity. Microchip design and device assembly were optimized for (1) the integration of permanent magnets to generate magnetic fields within the channel that efficiently trapped the aptamer-functionalized magnetic beads, and (2) the integration of a micropump to facilitate automated on-chip washing. Well plate format assays typically require labor-intensive, tedious, and time-consuming washing steps; integration of the assay into the microfluidic platform enabled rapid, automated washing. Assay parameters, such as reagent consumption and incubation time, were optimized in the microfluidic platform for the lowest limit of detection, highest specificity and shortest assay time. The analytical performance of the assay in the microfluidic format was compared to that in the well-plate format (generally utilized for ELISA-based methodologies). The microfluidic device proved to be a rapid and efficient system for aptamer-based assays, and required only minimal (microliter) reagent volumes. The work demonstrates the potential application of on-chip aptamer-based assays for detection of target proteins of biomedical importance.
9:00 PM - KK9.10
Seed Assisted Phase Control of TiOPc: Application of Microfluidic Mixing.
Enkhtuvshin Dorjpalam 1 , Hiroyuki Nakamura 1 , Kenichi Yamashita 1 , Masato Uehara 1 , Hideaki Maeda 1 2 3 Show Abstract
1 Micro- & Nanospace Chemistry Group, Nanotechnology Research Institute, National Institute for Advanced Industrial Science and Technology, Tosu, Saga, Japan, 2 Department of Molecular and Material Sciences, Interdisciplinary Graduate School of Engineering Sciences, Kyusyu University, Kasuga, Fukuoka, Japan, 3 CREST, Japan Science and Technology Agency, Hon-cho, Kawaguchi, Japan
In this study, we aim to tune crystalline phases of TiOPc nanocrystals prepared by re-crystallization process, through controlling structures of the seed particles. Y-phase TiOPc is a well recognized photoreceptor material. As an organic-molecular crystal, its preparation is very delicate process. In most cases, previously prepared seed particles are treated with various solvents so that the crystalline phase of interest is stabilized by means surface energy adjustment. However, this procedure often faces major difficulties with respect to reproducibility. Here, we have given importance to the structure of seed particles rather than post-treatment conditions. Microfluidic mixing is adopted for the seed preparation. Taking advantages of microfluidic reaction systems such as preciseness in heat and mass transfer as well as controllability and reproducibility of overall process, we attempted to prepare seed particles with a controlled structure and thus, tried to trace relations between the structures of seed particles and final product. For a seed preparation, commercial TiOPc was dissolved in conc. sulfuric acid and mixed with deionized water. Mixing was performed in a batch and micromixers. Seed particles were then isolated from the reaction mixture, washed thoroughly, soaked in a solvent media and dried to obtain a final product. During entire study, washing, soaking and drying conditions were kept identical. Structures of seed particles and final products were examined by UV-VIS and XRD. As evidenced by UV-VIS results, optical absorption of seed particles prepared using batch and micromixing under same temperatures shows obvious difference. In batch mixing regardless of mixing temperature, a mixture of various metastable structures was obtained. We assume this might be the reason why preparation of Y-TiOPc by batch type solution processes fell short in reproducibility. On the other hand, when micromixing is used, it was possible to control structures of the seed particles by means of adjusting mixing temperature. Well distinguished amorphous (4oC) and α-phase (90oC) seed particles were obtained. Early stages of structure evolution are monitored in-situ by on-flow UV-VIS spectroscopy in a sub-millisecond time scale. First signs of α-phase evolution is detected as fast as 8 ms after mixing. Further we have checked effects of micromixer types on the heat dispersion during mixing and seed structure. In conclusion, by means of using microfluidic mixing for the seed preparation, in other words, by means of ensuring controllability and reproducibility during during initial precipitation of seed particles it was possible to tune crystalline phases of TiOPc. Mixing pattern and mixing temperature are essential parameters that affect seed particle`s structure. Seed particles with an amorphous structure or that is not contaminated with α-phase tend to precipitate in Y-phase with a good reproducibility.
9:00 PM - KK9.12
Control of the Surface Properties of Microfludic Devices by Using Polyelectrolyte Multilayer Coatings.
Sung Yun Yang 1 Show Abstract
1 , Chungnam National University, Daejeon Korea (the Republic of)
Recently, more studies have been conducted in chemical and biological applications using microfluidic or nanofluidic devices. However, it is still challenging to control of the surface properties of these devices on demand. In this paper, we utilized layer-by-layer deposition method to modify the surface of the micro-channel of the device in order to control cellular interactions inside of the channel. We have been studied cellular interactions on various polyelectrolyte multilayer films on open surfaces. In the cell study, some polyelectrolyte multilayer films exhibited cell-blocking ability. We applied these excellent biocompatible coating on micro-channeled devices. Multilayer films comprised of weak polyelectrolytes exhibit different surface properties as they were assembled at different pH conditions. Therefore, cellular interactions including adhesion can be shown differently by depending on the PEM surfaces. Polyelectrolytes including biodegradable polymer such as poly(hyaluronic acid) (HA) was investigated for their surface-cell interaction using epithelial cells and immune cells.
9:00 PM - KK9.2
Formation of Hydrogel Droplet Utilizing Microfluidic Device for Simultaneous Detection of Phenol Compounds.
Eun-Ji Jang 1 , Sun-A Park 2 , Yeol Lee 1 , Sang-Phil Park 1 , Bum-Sang Kim 2 , Won-Gun Koh 1 Show Abstract
1 Biomolecular & Chemical Engineering , Yonsei University, Seoul Korea (the Republic of), 2 Chemical Engineering , Hongik University, Seoul Korea (the Republic of)
We developed a microfluidic device for the detection of phenol that incorporates hydrogel microparticles entrapping quantum dot (QD)-conjugated tyrosinase. The microfluidic device is designed to have two parts; one for the production of hydrogel microspheres, and the other for the quantitative detection of phenol. The first part of a device has T-junction configuration where the inlet channel containing the dispersed phase perpendicularly intersects the main channel which contains the continuous phase to produce droplets of hydrogel precursor solution, which were subsequently crosslinked by UV exposure and moved to the second part of a device. The size of hydrogel spheres was ranged from 50 to 100 um by altering the fluid flow rates, the channel widths, or by changing the relative viscosity between the two phases. The second part was microfilter-integrated chamber and all the hydrogel microspheres were effectively retained within the chamber by using microfilter with smaller mesh size than hydrogel microspheres. The detection of phenol was based on the quenching effect of o-quinone. When phenol diffuses into hydrogel microspheres entrapping QD-conjugated tyrosinase, it is oxidized to o-quinone by tyrosinase-catalyzed reaction, which is a classic electron accepting chemical that can quench the fluorescence of QDs within the hydrogel microspheres. It was found that degree of QD quenching was proportional to phenol concentration and wide range of phenol concentration (10 nM – 10μM) could be detected within a microfluidic device.
9:00 PM - KK9.3
Biomolecular Nanopatterning by Microfluidic System Guided Magnetic Electric Lithography.
Zhen Gu 1 2 3 , Yong Chen 1 3 Show Abstract
1 Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, Los Angeles, California, United States, 2 Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, California, United States, 3 California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California, United States
Biomolecular nanopatterning technique holds enormous promise for biological and medical applications, including high-sensitive diagnostics, genomics, proteomics, and integrated biomaterials. Here we have developed a magnetic electric lithography (MEL) technique, in which MNPs coated with multiple distinct biomolecules can be conveniently delivered through a microfluidic system, speedily deposited onto a template surface within specific areas by a magnetic field, and selectively immobilized onto the nanoelectrodes by applying an electric potential on the electrodes. Heterogeneous biomolecular nanopatterns formed by the MNPs assembled on the nanoelectrodes can be reliably transferred to a biocompatible polymer substrate. We have demonstrated that nanopatterns with a resolution down to ~10 nm can be fabricated by MEL, and heterogeneous biomolecular nanoarrays can be obtained by a parallel MEL process over an area of ~0.5 cm2 within two minutes. The resolution can potentially be improved by further reducing the sizes of MNPs and nanoelectrodes on the template. An integrated MEL system with dynamically controlled magnetic field, electric potential, and multiple microfluidic channels can potentially fabricate complex on-demanding biomolecular nanopatterns with high resolution, speed, and throughput for various biological and medical applications.
9:00 PM - KK9.4
Numerical Simulations of Misalignment Effects in Microfluidic Interconnects.
Sudheer Rani 1 3 , Taehyun Park 1 3 , Byoung Hee You 1 4 , Steve Soper 2 3 , Michael Murphy 1 3 , Dimitris Nikitopoulos 1 3 Show Abstract
1 Department of Mechanical Engineering, Louisiana State University, Baton Rouge, Louisiana, United States, 3 Center for Bio-Modular Multi-Scale Systems, Louisiana State University, Baton Rouge, Louisiana, United States, 4 Department of Engineering Technology, Texas State University, San Marcos, Texas, United States, 2 Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana, United States
The need to provide fluidic interconnections is one of the most important issues in the successful realization of an integrated microfluidic device. Numerical simulations were performed to see the effect of geometrical misalignment in pressure driven flows. The various types of misalignment effects investigated were the ones arising during: end-to-end interconnection, channel overlap when chips are stacked on top of each other, and the misalignment occurring due to the offset between the external tubing and the reservoir. For the case of end-to-end interconnection, the effect of misalignment was investigated for 0, 13, 50, 58, and 75% reduction in the available flow area at the location of geometrical misalignment. The formation of recirculation regions resulted in huge pressure drop as the amount of misalignment increased and this in greatly enhanced in the case of 75% reduction in available flow area at the misalignment junction. For the second case of misalignment due to channel overlap, various misalignment configurations were simulated by maintaining the same amount of misalignment (75% flow area reduction) for all the configurations. Calculations of equivalent length and loss coefficients showed that the effect of geometric misalignment is independent of the configuration and only depends on the flow area ratio (i.e. ratio of available flow area at misalignment to the original channel cross-sectional area) and the Reynolds number. The effect of misalignment between the centers of reservoir and external tubing was investigated by varying the position of the tubing to two different locations relative to the center of the reservoir. The effect of Reynolds number was also taken into account by simulating all the aforementioned cases at different Reynolds numbers ranging from 0.075 to 75. All the results are evaluated in terms of the equivalent length of a straight pipe and loss coefficients. The effect of misalignment in tube-in-reservoir interconnection was found to be insignificant when compared to the other two cases of interconnection.Correlations were developed for all the cases which are purely function of flow area ratio and Reynolds number. This enables the determination of pressure drop for arbitrary channel cross-sections and any amount of misalignment.
9:00 PM - KK9.5
Hot Embossing of Microfluidic Channel Structures in Cyclic Olefin Copolymers.
Patrick Leech 1 , Xiaoqing Zhang 1 , Yonggang Zhu 2 Show Abstract
1 , CSIRO CMSE, Clayton, Victoria, Australia, 2 , CSIRO CMSE, Highett, Victoria, Australia
Cyclic Olefin copolymer (COC) has become a promising substrate in microfluidic devices because of it's unique optical and mechanical properties which can be tuned by variation in the norbornene/ ethylene ratio. This paper examines, for the first time, the relationship between composition of synthesized grades of COC, the viscoelastic/ thermal properties and the replication of channel structures by hot embossing. The six grades of COC used in these experiments have contained a widely varying norbornene content (61-82 wt %) and glass transition temperature, Tg, (75-175 °C). Dynamic mechanical thermal analysis (DMTA) of these copolymers has shown a distinct change in the storage (E′) and loss (E″) moduli and loss tangent (tan δ) as a function of wt % norbornene. An optimal range of temperature for hot embossing (≥20 °C above Tg) has been identified from DMTA. In this temperature range, all grades of copolymer have shown a negligible elastic modulus, E′, and a low and constant value of viscous flow modulus (E″). Polymer deformation was studied during the hot embossing of 50, 100 and 200 µm channel widths. Hot embossing at temperatures above Tg, in a region of viscous liquid flow, has produced a smooth surface morphology and a full replication of depth without cracking or distortion of the channels in each grade of COC. The application of these results in the fabrication of flow focusing junctions  will be discussed in the paper.  P.W. Leech J.Micromech.Microeng. 19(6) 065019 (2009).
9:00 PM - KK9.6
Microfluidic-Microelectrode Array Devices for Culture of Unidirectional Neuronal Networks.
Alexander Mo 1 , Sarah Heilshorn 1 Show Abstract
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
The brain consists of a multitude of networked cells that work together to regulate bodily functions and centralize decision making. Individual neurons differentiate into specialized phenotypes that make multiple connections with other neurons to form circuits. These circuits in turn are wired to other circuits that regulate related functions in the body, forming a network with control over entire bodily systems. While much work has been done to piece together this hierarchical network connectivity across multiple length scales, efforts at studying simple cellular-level circuits have been hampered by the limited number of tools available to build in vitro circuit models. In response, we have designed microfluidic/microelectrode array devices to enable the formation of simple living neuronal networks. The microfluidic device portion dictates the connectivity of the network while the microelectrode array is used to both perturb and record the network activity. This device was designed to enable the formation of hierarchical, unidirectional connections between two isolated groups of randomly networked neurons.The PDMS microfluidic device, fabricated using standard soft lithography protocols, contains two cell culture chambers (2000 μm wide, 600 μm long, 100 μm tall) spaced 400 μm apart that are connected by 66 axonal microchannels (~10 μm wide, 5 μm tall). Similarly sized axonal microchannels developed by Jeon et al. were found to enable axonal neurites to extend through the tunnels while restricting the migration of cell bodies and dendrites. The PDMS microfluidic device is then bonded to a commercially fabricated planar microelectrode array (pMEA) to form two isolated cell culture environments for two specific neuronal phenotypes. Initially, a single neuronal phenotype is injected into the first chamber, and the neurons are allowed to mature and send axons through the microchannels. Following this, a secondary seeding of neurons is injected into the other chamber, and the cultures are incubated to allow the formation of synaptic connections between the two cell populations. This designed hierarchical network structure should be capable of stimulating and recording axon-mediated, unidirectional electrical signaling between two otherwise isolated networks of neurons.Compared to other recently developed methods to pattern neuronal cultures (e.g., microstamping and single-cell positioning), this method is cost-effective and can be easily multiplexed for high through-put experiments. Furthermore, because the device is fabricated from transparent materials, the neurons can be imaged in real-time to monitor morphological changes that occur during network remodeling and to correlate these changes with electrical network activity. This work represents a first step towards developing in vitro neuronal circuit models with pre-determined, hierarchical network connectivity.
9:00 PM - KK9.7
High Aspect Ratio SU8 Negative Photoresist Microstructures Manufactured by a New Method Plasma Assisted SU8 Etching.
Saydulla Persheyev 1 , Mervyn Rose 1 Show Abstract
1 Electronics Engineering and Physics, University of Dundee, Dundee, Angus, United Kingdom
SU8 Negative photoresist is finding high demand in applications such as MEMS, sensors and waveguides.The possibility of photolithographic patterning and high physical and dielectric properties are attracting ever more users among workers in the electronics industry and increasingly in biomedical applications. The negative epoxy-based SU8 photoresist, due to its special mechanical properties such as durability, water impermeability and dielectric nature upon polymerisation, is often used as a resin for making high aspect ratio, functional MEMS (Micro-Electro-Mechanical Systems) device structures and packaging, for cantilevers, and “Lab-on-a-chip” systems. SU8 is ideally suited to the fabrication of devices for micro-fluidic devices and in bio-MEMS, due its biocompatibility and chemical resistance. The negative photoresist is structured by UV photolithography and structures consisting of multiple layers can be created. The common issues that need to be overcome for conventional through top mask exposure is low adherence for low exposure times and top feature T shape broadening (a phenomenon known as T-topping) for overexposed films. Another limitation is low structure profile flexibility while the same mask is applied. In our work we employ an original method of exposing of SU8 and create high aspect ratio structures on glass and other substrates. Dry plasma etching results of negative epoxy-based photoresist by Reactive Ion Etching and Inductively Coupled Plasma system using gases O2 and CF4 are presented.
9:00 PM - KK9.8
Microfluidic Approaches for Bio-chemical Detection Sensors.
Kyung Choi 1 Show Abstract
1 , University of California, Irvine, California, United States
In nanotechnology, there are a lot of efforts for developing smaller and more compact devices to meet our growing demands in miniaturization. New advances such as soft lithography and microfluidic approaches thus have gotten great attentions to fabricate smaller devices with enhanced performances. There are challenges in nanotechnology for chemists to develop new materials since the technology is a part of the chemical domain, which builds up novel materials at the molecular level. Microfluidic approaches have taken intensive attractions since microfluidic reactors allow us to produce novel materials with specific advantages. We present here a microfluidic particle synthesis of molecularly imprinted polymer (MIP) with high affinities in molecular recognitions for bio- or chemical detection sensors/device applications. Molecularly imprinted polymer can be provided by “molecular imprinting technique”, which is a general protocol for the creation of synthetic receptor sites with specific molecular recognition functions for organic or bio-molecules in cross-linked network polymers. Synthesis of high affinity receptor sites is a key contribute to achieve high sensitivity in their molecular recognition functions.
9:00 PM - KK9.9
The Use of Microreaction Technology for Synthesis of Aromatic Nitro-plasticizer.
Toshiyuki Ogura 1 , Toshihiko Ohta 1 , Yutaka Takahashi 2 , Kazuhiro Mae 3 Show Abstract
1 Taketoyo plant, NOF corporation, R and D department, Aichi Japan, 2 Division of Mechanical Engineering, Gradiate School of Engineering, Mie University, 1677 Kurima Machiya-cho, Tsu, Mie Japan, 3 Department of Chemical Engineering, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto Japan
In order to keep process safety in exothermic chemical process such as nitration reaction, it is indispensable to restrain violent reaction. This is often troublesome through the process of scale-up of the conventional batch system from experimental size to productive scale. Micro system has the advantage to avoid the violent reaction by high heat-exchangeability. Numbering-up of micro device enables to increase the productivity with keeping process safety. In addition, high selectivity is also expected because micro mixing achieves homogeneous reaction circumstances and reaction condition within shorter period than milli-seconds.In the reaction system using aqueous acids, small diffusion distance generated in laminar flow in micro channel is effective for the reaction with hydrophilic reaction substrate. However, more vigorous mixing is needed in the system of immiscible substrates and nitration reactants or gas-liquid reaction system. We have been developed dynamically mixing microreactor suitable for these reaction systems.In this study, we have evaluated the mixing property of the developed microreactor and utilized for aromatic nitration. Dynamically mixing microreactor developed here had the cylindrical reaction part made of PTFE whose channel width and length was 0.1 mm and 60 mm, respectively. When the inner rotor packed in the cylinder rotated to the several thousands of rpm, sheared flow was generated to form the Taylor-Couette flow and to make dynamical mixing which resulted in formation of micrometer-size droplets in immiscible fluids.Fine droplets promoted the nitration under the reaction temperature and the reaction would be quenched in tubing at downstream of microdevice by decreasing temperature and the agglomeration of droplets. The reactivity can be controlled by reaction temperature and flow rate of fluids.The microreactor was utilized for aromatic nitration of ethylbenzene and isopropylbenzene as the energetic plasticizers. Nitration reaction was conducted by mixing of the aromatic liquid with the mixture of sulfuric and nitric acid. These aromatic materials were completely converted, and the dinitro-derivatives could be synthesized at the yielding higher than 60% at the flow rate of several ml/min.
Carlos J. Martinez Purdue University
Sonia Grego RTI International
Alberto Fernandez-Nieves Georgia Institute of Technology
Joao Cabral Imperial College London
KK10: Devices and Materials Fabrication
Thursday AM, April 08, 2010
Room 3014 (Moscone West)
9:30 AM - **KK10.1
A New Class of Programmable Microfluidic Materials With Switchable Shape, Stiffness and Color.
Orlin Velev 1 , Suk Tai Chang 2 , A. Burak Ucar 1 , Frederick Renk 3 Show Abstract
1 Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Chemical Engineering & Materials Science, Chung-Ang University, Seoul Korea (the Republic of), 3 Center for Packaging Innovation, MeadWestvaco, Raleigh, North Carolina, United States
Microfluidic systems for bioanalysis, organic and nanoparticle synthesis have been widely investigated. The potential of microfluidics in other areas of technology, such as making materials with extraordinary adhesive and self-healing properties has only begun to be realized and explored. We will present a class of novel microfluidic materials in the form of flexible sheets that can be solidified by light or that can repeatedly change their color on demand. These materials are based on engineered microfluidic channel networks embedded into a matrix of thin sheets of polydimethylsiloxane (PDMS). The macroscopic properties of the elastomer are determined by the stiffness or color of the material in the microchannels. The microfluidic networks in the shape-locking sheets are filled with liquid photocurable polymer. The materials formed in this way possess the unique ability to "memorize" and retain user-defined shapes upon illumination. When the microchannel networks are deformed and exposed by UV light, the photoresist inside the channels is solidified and subsequently acts as endoskeleton within the PDMS layer, locking in the programmed shape. The bending and stretching moduli of the materials with solidified endoskeleton increase drastically. The permanent locking in of the shape of the microfluidic sheets could be used in making instant containers, creating "exoskeletons" for delicate devices, rapid prototyping and multiple other applications. We will also present new microfluidic materials that can switch controllably their color and transmittance in the visible and infrared range. The optical transmittance of these materials changes when colored solutions with different compositions displace each other by virtue of the laminar flow in the microchannel networks. Such "chameleon" microfluidic sheets can find applications in smart windows and energy management.
10:00 AM - KK10.2
Layer-by-layer Assembly for Stimuli-responsive Nanofluidic Devices.
Jonathan DeRocher 1 , Pan Mao 2 , Wui Siew Tan 3 , Jun Young Kim 3 , Sha Huang 4 , Jongyoon Han 4 5 , Michael Rubner 3 , Robert Cohen 1 Show Abstract
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 5 Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Microfluidic and nanofluidic devices hold great potential as a platform for manipulation and analysis of small sample volumes. The high throughput and high surface area possible with these devices suggests applications in biomolecule or chemical detection, selective separation, and heterogeneous catalysis. To realize some of this potential, the surfaces of these devices can be modified to impart functionality to the device. Polyelectrolyte multilayers (PEMs) can be used to impart a broad array of novel functionalities to a surface including stimuli-responsiveness, reversible switching of the gap thickness, manipulation of the sign and/or the density of the surface charge, chemical functionality and wettability of a surface.In this work, a hybrid micro/nanofluidic device which contains an array of parallel nanochannels has been used as a substrate for deposition of many different kinds of PEMs. We have successfully used layer-by-layer (LbL) assembly to produce uniform conformal coatings in channels with aspect ratios of up to 75 and widths as low as 200 nm. Polymer/polymer (homopolymers and/or block copolymers), polymer/nanoparticle, and nanoparticle/nanoparticle PEMs have all been deposited in confined channels. LbL assembly within submicron channels reveals interesting departures from what is seen for LbL growth on infinite planar surfaces and we explain this effect by surface charge-induced depletion of the adsorbing species in the confined channel at each stage of the LbL process. We have also successfully narrowed the channel width to the point at which further LbL processing produces no further growth on the channel walls, indicating that physical exclusion eventually becomes important. To form a stimuli-responsive device, LbL assembly of poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) at pH 9.3 was used to conformally coat the nanochannel walls. This PEM swells hysteretically and reversibly in response to pH changes. Both the kinetics and the extent of swelling were investigated using DC conductance and compared with films assembled on a planar, unconfined surface. Besides pH-responsive films, we are also investigating the incorporation of PEMs which swell in response to temperature changes.
10:15 AM - KK10.3
Fabrication and Applications of Three Dimensional Porous Microwells.
Christina Randall 2 , Yevgeniy Kalinin 1 , Anum Azam 2 , David Gracias 1 Show Abstract
2 Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 1 Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States
Conventional microwells are typically accessible only from one surface which can limit diffusion and interactions with the surroundings. This limitation is especially pronounced when cells are cultured in these wells. Here, we describe the design and applications of polyhedral (metallic or polymeric) microwells with any designed wall porosity. These microwells are truly three dimensional and we show that they have enhanced diffusion with the surroundings, thereby suggesting a need for these kinds of microwells in addition to conventional 2D microwell systems.
10:30 AM - KK10.4
Self-aligned Sub-lithographic Mask for Fabrication of Silicon Nanochannels.
Zhuojie Wu 1 , Paul Ho 1 Show Abstract
1 Microelectronics Research Center, The University of Texas at Austin, Austin, Texas, United States
Silicon nanochannels provide interesting fundamental science and promising technologies for nanofluidic studies. The development of silicon nanochannels is challenging due to lack of fabrication methods that are scalable, cost-effective, with fast throughput and compatible with conventional CMOS processes, yet producing nanochannels with high quality. A novel approach to fabricate silicon nanochannels to meet these requirements is presented in this study. The process starts with the use of a fluorocarbon plasma to form a sub-lithographic polymer mask which is self-aligned to predefined trenches. This is followed by wet anisotropic etching to yield nanotrenches with atomically smooth sidewalls along two edges of each predefined trench which is not required to be at nano-scale. Silicon nanotrenches have been fabricated with width down to 20nm range and aspect ratio as high as 20. The method is compatible with most lithographical techniques and has been implemented with optical and electron beam lithography. A simple non-conformal PECVD silicon dioxide deposition is used to seal the nanotrenches to form nanochannels. In addition, the height of the silicon lines between the nanotrenches can be controlled by varying the plasma conditions. By bonding to another substrate, both planar nanochannels and vertical nanochannels can be fabricated in a single lithographic step. Since each planar channel connects to two adjacent vertical channels, the effective aspect ratio can be increased to provide high flow rate without excessive pressure build-up in long channels. Potential applications of such silicon nanochannel structures will be discussed.
10:45 AM - KK10.5
Porous Silicon Membranes With Microcavity Array for Cell-trapping in Biomedical Sensors.
Heinz Wanzenboeck 1 , Slobodan Damnjanovic 1 , Emmerich Bertagnolli 1 , Michael Wirth 2 , Franz Gabor 2 Show Abstract
1 Institute for Solid State Electronics, Vienna University of Technology, Wien Austria, 2 Dept. of Pharmaceutical Technol. and Biopharmaceutics, University Vienna, Vienna Austria
Surface modification is an important step for “lab on chip” systems. Choice of material, surface features and topologies have been recognized to be of critical relevance for the cell-surface contact.With an established micro-structuring approach already successfully employed in microelectronic and MEMS fabrication, we describe a method for geometrical patterning of a silicon membrane. Utilizing anisotropic etching processes we generate a microcavity array on a silicon membrane. This provides a bio-friendly material and topography for not chemically but, geometrically enforced alignment of living cells on a surface. This mechanically robust and chemically insensitive membrane with microarrayed surface structure is evaluated as a new sensor architecture designed for whole-cell biosensors.Fabrication of the geometrical patterns on the sensor systems was achieved by lithographic patterning and anisotropic etching. Anisotropic KOH wet etching of Si is established as method in MEMS fabrication. Also reactive ion etching (RIE) using SF6 as etch species was employed to fabricate regular arrays of trench structures as well as protruding microcones.These microstructured silicon permeable membrane were provided as substrate for the growth of cell cultures. Human Caco-2 cells an epithelial cell line used as model of the human intestine - were seeded and directly grown on the fabricated porous membrane. The obtained results were investigated by optical microscopy and by scanning electron microscopy.While a planar substrate typically results in a cell layer distributed stochastically over the surface the fabricated samples with an array of conical microcavities provide a prestructured growth matrix for cell cultures. The effect of 3-dimensional structures on the spatial distribution of Caco-2 or bladder cells was evaluated and is compared to flat substrates. Experiments with trench structures indicate the feasibility to order and align Caco-2 cells on the microstructured surface of the porous membrane. Effects of various microstructure shapes and influence of geometrical parameters such as structure width and depth on the distribution of cells were investigated.With the presented approach of geometrical patterning of surface elements we have demonstrated the capability to provide a bio-friendly topography for cell-based sensor designs. The application of this novel concept for on-line monitoring sensors and for advanced microsensor arrays will be discussed. Microelectrodes on biochips present the core function for low cost bioelectrical analysis. Concepts to implement such measurement electrodes on the structured surface will be presented. The potential for an electrochemical measurement of individual cells will be discussed.
KK11: Particle Synthesis
Thursday PM, April 08, 2010
Room 3014 (Moscone West)
11:30 AM - **KK11.1
Encoded Microparticles for Multiplex Assays.
Patrick Doyle 1 Show Abstract
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
Microfluidic devices offer the ability to finely control physical and chemical conditions which is advantageous for microparticle synthesis. We have recently invented a new technique entitled Stop Flow Lithography (SFL) which couples microfluidics and projection lithography to create microparticles with chemical and geometric complexity. These particles can be both geometrically encoded and functionalized with biomolecules to create microparticles for use in multiplex assays. In this talk I will discuss our progress in both particle synthesis, particle performance in sensing assays and development of a flow scanner capable for orienting and reading the particles.
12:00 PM - KK11.2
Submicron Dielectrophoretic Ink-jet Printing of Colloidal Suspensions.
Niklas Schirmer 1 , Brian Burg 1 , Dimos Poulikakos 1 Show Abstract
1 Mechanical and Process Engineering, ETH Zurich, Zurich Switzerland
As an alternative to mechanically actuated printing, a novel method for the high precision droplet dispension of nanoparticle-laden liquids based on inhomogeneous electrostatic forces is presented. In contrast to pushing ink out of a reservoir as in state of the art inkjet printers, the present approach realizes liquid dispension and non-contact deposition of submicron structures through on-demand ejection from submicron capillary printheads. The inhomogeneity of an electric field at the sharp tip end of a capillary nozzle causes particles in the suspension to polarize and accelerate towards the highest gradient of the electric field (dielectrophoresis). Accelerated by electrostatic forces, these particle-laden liquids (nano-inks) form droplets at the end of the nozzle and are ejected to an underlying substrate. Once deposited on the substrate, the rapidly evaporating carrier liquid causes the nanoparticles to form precise structures. Printing of conductive, semiconducting, and non-conductive nanoparticle-based patterns is demonstrated and the physical behavior of the fabricated devices is investigated before and after necessary annealing steps. Depending on the triggering of the electrical field submicron patterns are produced by dropwise and continuous liquid ejection with feature sizes of less than 250 nm. Additionally, the technology is employed to print fluorescent particles for biological applications.In contrast to existing electrohydrodynamic printing technologies, this novel mechanism not only allows for the deposition of 2D but also of 3D structures well into the submicron range. Nanoparticles in the colloidal droplets combine under the action of van der Waals attraction forces on the substrate to form highly flexible vertical nanowires with controllable lengths and diameters, here in the range of 150–800 nm.
12:15 PM - KK11.3
Microfluidic Synthesis and Rheological Characterization of Non-spherical Organic Microparticles.
David Baah 1 , Kala Bean 1 2 , Nicole Walker 1 2 , Bernard Britton 1 2 , Julaunica Tigna 1 3 , Tamara Floyd Smith 1 2 Show Abstract
1 Materials Science & Engineering, Tuskegee University, Tuskegee, Alabama, United States, 2 Chemical Engineering, Tuskegee University, Tuskegee , Alabama, United States, 3 Mechanical Engineering, Tuskegee University, Tuskegee , Alabama, United States
The ability to synthesize large quantities of highly uniform nano- or micro-sized particles with a large diversity of customizable morphologies and physicochemical properties is a great asset to many advanced applications. Recent advancement in nanotechnology requires such uniform and customizable particles. However, the synthesis of such highly monodispersed particles with tunable functionalities has been a great challenge to the scientific community. Several reports have documented the synthesis protocols for various morphologies of inorganic nano- and micro-sized particles. Various heterophase polymerization methods including microemulsion and suspension polymerization have been developed and implemented to synthesize both polymeric particles and their composites. This polymerization approach does not offer control over the size and morphology, and has been primarily used to synthesize spherical particles. However, non-spherical particles are highly desired for their properties such as anisotropic responses to external fields, large surface area, and effective packing. Microfluidic technology presents an alternative approach to synthesizing non-spherical particles/composites with tunable functionalities. Using this approach, it is possible to synthesize colloidal based nano/microparticles and their composites with predetermined shapes usable in sensors, optical devices, and microelectromechanical systems (MEMS) and field-responsive rheological fluids. The method is dependent on the use of UV-curable prepolymer, with an appropriate photo-initiator. In this study, a photo mask patterned with pores defining the shape of the particles was used to block the UV light whilst the pores allow the passage of light thereby cross linking the liquid prepolymer in the path. The prepolymer solution was passed through a microfluidic device fabricated by bonding poly(dimethylsiloxane), PDMS, molds to a glass slide. The Olympus BX51WI Microscope was used, as a means of focusing the UV light, to synthesize micron sized cubic organic particles. The particles were found to be highly monodispersed and 100 micron cubic. Using a TA AR2000 Rheometer, the rheological characterization revealed a fairly constant viscosity in the shear rate range of 0.1-100 s-1. It is anticipated that a higher particle loading the effective packing and particle interaction will trigger the onset of shear thickening.
12:30 PM - **KK11.4
Microfluidic Assembly of Patterned Colloidal and Polymeric Microparticles.
Jennifer Lewis 1 Show Abstract
1 Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States
We are developing microfluidic-based assembly routes for creating patterned colloidal and polymeric microparticles, granules, and 3D micro-components. Several examples from our recent research activities will be highlighted. First, we will describe the microfluidic assembly of colloidal granules and other micro-components with controlled composition, shape, and size. Next, we will describe the creation of chemically patchy microparticles composed of distinct hydrophilic and hydrophobic features using stop-flow lithography. We will explore the effects of microparticle size, aspect ratio, and patchy morphology on their self-assembly and dynamics using confocal microscopy. Several potential applications of these methods will be demonstrated, including novel granular media and low-cost MEMs.