Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Y34: Focus Session: Microfluidics, Nanofluidics Applications |
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Sponsoring Units: DPOLY Chair: Alberto Fernandez-Nieves, Georgia Institute of Technology Room: 342 |
Friday, March 22, 2013 8:00AM - 8:36AM |
Y34.00001: Acoustic Microfluidics for Bioanalytical Application Invited Speaker: Gabriel Lopez This talk will present new methods the use of ultrasonic standing waves in microfluidic systems to manipulate microparticles for the purpose of bioassays and bioseparations. We have recently developed multi-node acoustic focusing flow cells that can position particles into many parallel flow streams and have demonstrated the potential of such flow cells in the development of high throughput, parallel flow cytometers. These experiments show the potential for the creation of high throughput flow cytometers in applications requiring high flow rates and rapid detection of rare cells. This talk will also present the development of elastomeric capture microparticles and their use in acoustophoretic separations. We have developed simple methods to form elastomeric particles that are surface functionalized with biomolecular recognition reagents. These compressible particles exhibit negative acoustic contrast in ultrasound when suspended in aqueous media, blood serum or diluted blood. These particles can be continuously separated from cells by flowing them through a microfluidic device that uses an ultrasonic standing wave to align the blood cells, which exhibit positive acoustic contrast, at a node in the acoustic pressure distribution while aligning the negative acoustic contrast elastomeric particles at the antinodes. Laminar flow of the separated particles to downstream collection ports allows for collection of the separated negative contrast particles and cells. Separated elastomeric particles were analyzed via flow cytometry to demonstrate nanomolar detection for prostate specific antigen in aqueous buffer and picomolar detection for IgG in plasma and diluted blood samples. This approach has potential applications in the development of rapid assays that detect the presence of low concentrations of biomarkers (including biomolecules and cells) in a number of biological sample types. [Preview Abstract] |
Friday, March 22, 2013 8:36AM - 8:48AM |
Y34.00002: Electrokinetic device for three-dimensional trapping of single fluorescent emitters Jason K. King, Brian K. Canfield, Lloyd M. Davis Trapping by use of actively controlled electric fields is a valuable tool for studies of single biological molecules and nanoparticles. Devices have been developed to trap in one and two dimensions, but these rely on physically constraining the molecule along one or more directions. However, behavior of trapped molecules may be perturbed due to high collision rates with walls. Here we report on the development of a three-dimensional (3D) electrokinetic trap to counteract Brownian motion. Two pairs of electrodes arranged in a crossed configuration on separate planes allow generation of an electric field of variable orientation and magnitude. A custom forward-illuminated microscope with astigmatism introduced to the tube lens is used to determine the nanoparticle's 3D position in real time. This device has demonstrated the capability to manipulate and confine single 40 nm fluorescent latex beads in glycerol-water solution. The use of an electron-multiplying CCD camera allows for faster detection rates (\textgreater 100 Hz) and single-photon sensitivity. Characterization of particle motion and performance analysis of trapping methods is investigated. The use of alternative 3D detection methods is discussed, as well as applications to studies of single biomolecules and nanoparticles. [Preview Abstract] |
Friday, March 22, 2013 8:48AM - 9:00AM |
Y34.00003: It may be possible to construct a Chemical Synthesizing Computer based on Capillary Action Richard Kriske This author had previously proposed that Capillary Action has a Quantum Mechanical Model. This model can be easily constructed by noting that when a photon of the heat wavelength evaporates one molecule of water at the top of a capillary column, a ``hole'' is transmitted from the top of the column to the roots and into the water reservoir sustaining the capillary tube. This ``hole'' is a true hole (a true particle) in that it is transmitted as a quantized unit through the capillary tube. The mathematics of this process are the same as used in Quantum Field Theory, with the capillary acting as a perfect spring (like the spring used on a ``stack'' of dishes). When the external field using a force to pull the water molecule off the stack, an equal and opposite spring force (which is quantized), is transmitted down the column to the reservoir. When the water is not pure, this author proposes that each of the elements in the unpure water act linearly, each with its own quantized spring constant that does not interact with the other quantized spring constants, so it is possible to pull a single electron off the top of the water stack, yet the water in the stack is undisturbed (the reservoir is disturbed). Likewise it is possible to pull a sugar molecule off and balance chemical equations. [Preview Abstract] |
Friday, March 22, 2013 9:00AM - 9:12AM |
Y34.00004: ABSTRACT WITHDRAWN |
Friday, March 22, 2013 9:12AM - 9:24AM |
Y34.00005: Integrated optics for Lab-On-Chip Yu Gu, Andrea Crespi, Lisa Mariani, Gianna Valentino, Giulio Cerullo, Roberto Osellame The miniaturization of traditional chemical and biochemical functionalities called Lab-On-Chip has many advantageous over existing methods, such as portability, small sample size, multiplexing and simpler automation and standardization. In recent years, the integration of microfluidic and microoptical elements together onto monolithic platforms has led to the new term optofluidics. We present novel optofluidic devices based on integrated waveguides, microfluidic channels and high-index fluids. Such devices have a variety of applications including label-free biochemical sensing and telecommunications. [Preview Abstract] |
Friday, March 22, 2013 9:24AM - 9:36AM |
Y34.00006: A microfluidic separation platform using an array of slanted ramps Sumedh Risbud, Jorge Bernate, German Drazer The separation of the different components of a sample is a crucial step in many micro- and nano-fluidic applications, including the detection of infections, the capture of circulating tumor cells, the isolation of proteins, RNA and DNA, to mention but a few. Vector chromatography, in which different species migrate in different directions in a planar microfluidic device thus achieving spatial as well as temporal resolution, offers the promise of high selectivity along with high throughput. In this work, we present a microfluidic vector chromatography platform consisting of slanted ramps in a microfluidic channel for the separation of suspended particles. We construct these ramps using inclined UV lithography, such that the inclined portion of the ramps is upstream. We show that particles of different size displace laterally to a different extent when driven by a flow field over a slanted ramp. The flow close to the ramp reorients along the ramp, causing the size-dependent deflection of the particles. The cumulative effect of an array of these ramps would cause particles of different size to migrate in different directions, thus allowing their passive and continuous separation. [Preview Abstract] |
Friday, March 22, 2013 9:36AM - 9:48AM |
Y34.00007: Size based separation of micro-particles using adhesive ciliated surfaces: Mimicing the behaviour of suspension feeders Anurag Tripathi, Amitabh Bhattacharya, Anna Balazs Separation of different size micro-particles in microfluidic devices is important for many biomedical applications. Inspired by the selective intake of small food particles by marine suspension feeders, we propose a novel separation mechanism of micro-particles using active cilia arrays with adhesive tips. By means of Lattice Boltzmann simulations, we show that mixture of two different size particles with size ratio greater than or equal to two can be nearly completely separated by tuning adhesion strength and cilia stiffness. The proposed technique can be used even at low Reynolds number (Re $\ll$ 1) where separation mechanisms based on inertial effects will be of little use. For a given cilia-particle interaction, the balance of hydrodynamic and adhesive forces favors capture of particles below a critical size, which can be predicted by a simple analytical model. [Preview Abstract] |
Friday, March 22, 2013 9:48AM - 10:00AM |
Y34.00008: Stiffness Dependent Separation of Cells in a Microfluidic Device Todd Sulchek, Gonghao Wang, Wenbin Mao, Alexander Alexeev Abnormal cell mechanical stiffness can point to the development of various diseases including cancers and infections. We report a high-throughput technique for continuous cell separation utilizing variation in cell stiffness. We use a microfluidic channel that is decorated by periodic diagonal ridges to force cells of different stiffness values to follow different trajectories. The ridges within the microfluidic flow channel compress and deform the cells in rapid succession to translate each cell perpendicular to the channel axis in proportion to its stiffness. We report the experimental demonstration of separation as well as computational validation of the mechanism of separation. Atomic force microscopy (AFM) was used to independently measure cell stiffness. By flowing cells through the microfluidic device, we can quickly and efficiently separate mixtures into subpopulations of stiff cells and soft cells. We then summarize how we expect this technology may produce new biomedical diagnostic capabilities. [Preview Abstract] |
Friday, March 22, 2013 10:00AM - 10:12AM |
Y34.00009: Process development for perfectly concentric droplets-within-droplets and uniform-walled shells Greg Randall, Brent Blue Compound droplets, or droplets-within-droplets, are currently precursors for shell targets used in intertial fusion experiments. To implode properly, each shell requires a uniform wall thickness, which in turn requires a centered core droplet in the compound droplet precursor. Previously, Bei et al. (2009, 2010) have shown that stationary compound droplets could be centered in a static fluid using an electric field of 0.7 kV/cm at 20 MHz. We present our recent results in developing a continuous microfluidic process to mass fabricate these uniform-walled shells. This includes: using electric fields to center the core of moving compound droplets, inhibiting droplet stretching by using protein emulsifiers, and maintaining a centered core during polymerization. We apply a physical scaling analysis from a fluid mechanics perspective to aid process design. [Preview Abstract] |
Friday, March 22, 2013 10:12AM - 10:24AM |
Y34.00010: Optical Nanodozers: A New Tool for Probing Single-Molecule Conformation and Confinement Free Energy in Cavities of Adjustable Nanoscale Dimension Ahmed Khorshid, Walter Reisner Experiments probing single-molecule DNA statics and dynamics in nanoconfined systems are typically performed via fluoresence microscopy, yielding access to information regarding molecule conformation but no direct information regarding nanoscale forces. In our experiment we combine two single-molecule manipulation tools, optical trapping and nanoconfinement, to develop a novel assay that can yield information regarding both molecule conformation and forces experienced in confinement. Polystyrene beads are trapped inside 300x300nm silica nanochannels. These beads are then used as ``nano-pistons'' or ``nanodozers,'' to apply compressive forces to single-molecules confined inside the nanochannels. In particular, a single nanodozer is used to push a DNA molecule against a nanoslit barrier, enabling measurements of force versus molecule compression. By carefully calibrating our trap via assessing Brownian motion of the nanochannel confined bead we are able to obtain a force-compression curve that we are comparing to polymer physics models for a cavity confined chain. In addition, we can determine the force required to drive the polymer across the entropic barrier as the critical force applied when the polymer jumps out of the cavity and over the slit. [Preview Abstract] |
Friday, March 22, 2013 10:24AM - 10:36AM |
Y34.00011: DNA in Nanochannels: A Multistage Free Energy Perturbation Approach Yanwei Wang, Douglas R. Tree, Kevin D. Dorfman Nanochannels are ideal platforms for studying the basic physics of confined polymers, using DNA as the model polymer. While the scaling laws for strong (Odijk) and weak (de Gennes) confinement were established decades ago, recent experiments and computer simulations have illuminated the complex physics arising between these limiting cases. To understand fully the transition region between the classical regimes of de Gennes and Odijk, it is necessary to examine the underlying free energy behavior of DNA in nanochannels. This presentation reports our studies on the confinement free energy and other properties of nanochannel-confined DNA by the multistage free energy perturbation (MFEP) technique. Emphases are focused on the methodology, the role of the aspect ratio of the channel on the confinement free energy and the force-extension relation of DNA confined in nanochannels. [Preview Abstract] |
Friday, March 22, 2013 10:36AM - 10:48AM |
Y34.00012: Molecular Dynamics Study of Polymer Separation Using a Nanofluidic Staircase Frederick Phelan Jr., Christopher Forrey The diffusive behavior of isolated polymer chains in a nanofluidic staircase has recently been studied experimentally [Strychalski et al., Macromolecules, 45(3), 1602, (2012); Stavis et al., Lab Chip, 12(19), 1174, (2012)] and by simulation [Phelan et al., in preparation, (2012)]. Chains are observed to exhibit spontaneous 1-D biased diffusion from regions of high to low confinement, without the use of external forces, under conditions where the local confinement lies in either the Odijk or de Gennes regimes. The transport mechanism is that of a Brownian motor, where the polymer free energy is used to generate directed transport using thermal fluctuations and the biased structural features of the device. The nanostaircase has potential for a number of applications in polymer measurement science and transport, an important one of which could be separations. To study this, we examine polymer separation in the nanofluidic staircase using the molecular dynamics simulation software LAMMPS. Length based separations of linear polymers as applicable to DNA separations are the main topic of the study, but the effect of more complex architectures such as branching are also examined. [Preview Abstract] |
Friday, March 22, 2013 10:48AM - 11:00AM |
Y34.00013: Measuring the confinement free energy of DNA in nanofluidic cavities Alexander Klotz, Walter Reisner It is possible to dictate the equilibrium conformation of single DNA molecules in nanofluidic systems by creating topographies where confinement varies over scales of nanometers to microns. Much work has been done to elucidate the polymer physics of systems with simple 1D or 2D confinement, but there is little quantitative understanding of behavior in more complex systems.~ Using single-molecule fluorescence microscopy, we study the equilibrium conformation of single DNA molecules partitioning into a single nanoscale pit etched in a nanoscale slit. In this system the polymer exists in a conformation which is partially occupying the nanopit and partially outside in the slit: the fraction of contour filling the pit is determined by a balance of confinement free energy and self-avoidance.~ We measure statistical distributions of this filling fraction resulting from fluctuations of contour in and out of the slit. These distributions are measured as a function of slit height and pit width and interpreted in terms of free energy models based on the balance of confinement free energy and self-avoidance.~ These measurements serve as a unique experimental probe of cavity-like polymer confinement, a system with rich phase behavior that has not been probed experimentally.~ Together with previous work on the statistics of molecules spanning multiple pits, we can use this system to make measurements of the free energy of confinement and self-avoidance effects in confined systems, essential quantities in the design of nanofluidic devices for DNA manipulation. [Preview Abstract] |
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