Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 55, Number 16
Sunday–Tuesday, November 21–23, 2010; Long Beach, California
Session GP: Microfluids: Fluidic Devices I |
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Chair: Prashanta Dutta, Washington State University Room: Long Beach Convention Center 203A |
Monday, November 22, 2010 8:00AM - 8:13AM |
GP.00001: Continuous Size-Based Particle Separation in a Microfluidic Device Barukyah Shaparenko, Han-Sheng Chuang, Howard Hu, Haim Bau, George Worthen Pinched flow fractionation is a continuous particle sorting technique in which two streams (one with particles, the other without particles) are manipulated to meet and then flow collinearly through a pinched microchannel. Due to geometric constraints, the particles align at different positions relative to the channel wall, with smaller particles closer to the wall than larger particles. Following the pinched segment, the channel broadens significantly, and the differences in particle positions are amplified as the particles follow the diverging fluid streamlines and are separated into different outlet channels based on their sizes. We analyze the separation of 2 and 10~$\mu$m rigid spherical particles with a pinched segment of 40~$\mu$m width, comparing 2D computational results and experimental results. We control the separation by specifying an inlet flow rate ratio and one outlet flow rate. We optimize the channel geometry and determine the operating parameters necessary to achieve effective particle separation. Multiple stages of such separation components can be integrated for finer separations. Other separation mechanisms, like dielectrophoresis, can also be integrated into the device using field flow fractionation, in which an external field is applied perpendicular to the direction of flow, causing the particles to cross fluid streamlines. [Preview Abstract] |
Monday, November 22, 2010 8:13AM - 8:26AM |
GP.00002: Numerical simulations of the separation of deformable particles in deterministic lateral displacement devices Keng-Hwee Chiam, Raymond Quek, Duc Vinh Le Using numerical simulations, we study the separation of deformable bodies, such as capsules, vesicles, and cells, in deterministic lateral displacement devices, also known as bump arrays. These arrays comprise regular rows of obstacles such as micropillars whose arrangements are shifted between adjacent rows by a fixed amount. We show that, in addition to the zigzag and laterally displaced trajectories that have been observed experimentally, there exists a third type of trajectory which we call dispersive, characterized by seemingly random bumpings off the micropillars. These dispersive trajectories are observed for large and deformable particles whose diameters are comparable to the gap size between micropillars. We then map out the regions in phase space, spanned by the row shift, particle diameter, and particle stiffness, in which the different types of trajectories are expected. We also shown that, in this phase space, there are transitions from zigzag to dispersive trajectories, bypassing lateral displacement. This is undesirable experimentally because it limits the ability of the device to fractionate. Finally, we discuss how our numerical simulations may be of use in device prototyping and optimization. [Preview Abstract] |
Monday, November 22, 2010 8:26AM - 8:39AM |
GP.00003: Long Chain DNA Separation in a Sparse Nanopost Array Jia Ou, Mark Joswiak, Kevin Dorfman Long chain DNA separation is a challenge for gel lectrophoresis. Our previous DNA separation experiments and simulations demonstrated that a sparse micro post array can separate large DNA. However, the smaller DNA are not well resolved. We hypothesized that smaller posts will increase the collision frequency of the smaller DNA and thus the resolution. We successfully fabricated a hexagonal array of 350 nm diameter posts with a 3 $\mu $m spacing using an oxygen plasma etching method. Under an electric field of 10 V/cm, the mobilities of different species ranging from 10-48.5 kilobasepair (kbp) were normalized by the mobility of $\lambda $ DNA (48.5 kbp), which was included in all experiments as a standard to correct for day-to-day variations in electroosmotic flow. The resolution of these DNA is markedly improved when compared with a 1 $\mu $m diameter micropost array. We demonstrate the robustness of the device by using the calibration curve to identify the peaks in a separation of the $\lambda$ DNA-Mono Cut mix. [Preview Abstract] |
Monday, November 22, 2010 8:39AM - 8:52AM |
GP.00004: Modeling the electrophoretic separation of short biological molecules in nanofluidic devices Ghassan Fayad, Nicolas Hadjiconstantinou Via comparisons with Brownian Dynamics simulations of the worm-like-chain and rigid-rod models, and the experimental results of Fu et al. [{\it Phys. Rev. Lett.}, {\bf 97}, 018103 (2006)], we demonstrate that, for the purposes of low-to-medium field electrophoretic separation in periodic nanofilter arrays, sufficiently short biomolecules can be modeled as point particles, with their orientational degrees of freedom accounted for using partition coefficients. This observation is used in the present work to build a particularly simple and efficient Brownian Dynamics simulation method. Particular attention is paid to the model's ability to quantitatively capture experimental results using realistic values of all physical parameters. A variance-reduction method is developed for efficiently simulating arbitrarily small forcing electric fields. [Preview Abstract] |
Monday, November 22, 2010 8:52AM - 9:05AM |
GP.00005: Continuous separation of micropaticles by size in ridged microchannels Wenbin Mao, Gonghao Wang, Todd A. Sulchek, Alexander Alexeev Size-based separation and sorting are widely used for biomedical research and clinical application. We design a microfluidic channel with periodically arranged diagonal ridges that separate micrometer-sized particles by size. We use a hybrid numerical method that combines the lattice Boltzmann model (LBM) and lattice spring model (LSM) to examine the dynamics of suspended particles in such channels. Our simulations reveal that particles with different sizes follow distinct trajectories and separate in the lateral direction inside ridged microchannels. The trajectories are determined by the particle equilibrium position in narrow constrictions formed diagonal ridges. We characterize the separation performance by analyzing the effects of ridge geometry and compare our simulation results with experimental data. This microfluidic system can be employed for high throughput sorting and separation of biological cells and synthetic microcapsules. [Preview Abstract] |
Monday, November 22, 2010 9:05AM - 9:18AM |
GP.00006: Continuous Electrokinetic Separation of Particles and Cells in a Serpentine Microchannel Cameron Canter, Junjie Zhu, Tzuen Rong Tzeng, Xiangchun Xuan Particle separation plays an important role in many areas. A variety of force fields have been used to separate particles in microfluidic devices, among which electric field may be the most popular one due to its general applicability and adaptability. So far, however, electrophoresis-based separations have been limited to primarily batchwise processes. Dielectrophoresis (DEP)-based separations require in-channel micro-electrodes or micro-insulators to produce electric field gradients. In this talk we present a novel electrokinetic separation of particles in a serpentine microchannel. The continuous separation arises from the cross-stream particle dielectrophoresis induced by the non-uniform electric field inherent to curving microchannels. We demonstrate a size-based separation of polystyrene beads (1 $\mu $m and 5 $\mu $m in diameter) and microbial cells (\textit{E. coli} and yeast) in the serpentine microchannel with the application of a small DC electric field. We also develop a numerical model to simulate the particle and cell separation processes. [Preview Abstract] |
Monday, November 22, 2010 9:18AM - 9:31AM |
GP.00007: Electrokinetic Transport and Manipulation of Particles in Microfluidic Reservoirs Junjie Zhu, Xiangchun Xuan Electrically controlled microfluidic devices have been proven to be very useful in manipulating both synthetic and biological particles in terms of efficiency, sensitivity, and simplicity. The success of these devices depends on a comprehensive understanding of electrokinetic particle transport in every part of their microchannels and reservoirs. In this talk we present an experimental and numerical study of the electrokinetic transport of spherical polystyrene beads in microfluidic reservoirs. We also demonstrate that polystyrene beads can be continuously focused, trapped, concentrated, and separated in microfluidic reservoirs. This diverse electrical control of particle transport in reservoirs is envisioned to open new possibilities for handling bioparticles in electrokinetic microfluidic systems. [Preview Abstract] |
Monday, November 22, 2010 9:31AM - 9:44AM |
GP.00008: Optoelectrofluidic field separation based on light-intensity gradients and its applications Jinsung Yoon, Sanghyun Lee, Kwan Hyoung Kang Optoelectrofluidic field separation (OEFS) of particles under light-intensity gradient (LIG) is reported, where the LIG illumination on the photoconductive layer converts the short-ranged dielectrophoresis (DEP) force to the long-ranged one. The long-ranged DEP force can compete with the hydrodynamic force by alternating current electro-osmosis (ACEO) over the entire illumination area for realizing effective field separation of particles. Results of the field separation and concentration of diverse particle pairs (0.82--16 $\mu $m) are well demonstrated, and conditions determining the critical radius and effective particle manipulation are discussed. In addition, expanding the OEFS to biological applications such as rapid cell manipulation and separation will be discussed. The OEFS with LIG strategy could be a promising manipulation method of particles including biological cells in many applications where a rapid manipulation of particles over the entire working area is of interest. [Preview Abstract] |
Monday, November 22, 2010 9:44AM - 9:57AM |
GP.00009: Deterministic Particle Trapping in Laminar Microvortices Albert Mach, Dino Di Carlo We present a method of deterministic trapping of particles larger than a critical size in laminar microscale vortices. This novel phenomenon is observed in microchannels containing a straight channel with periodic expansion and contraction arrays. High fluid flow rates in the laminar regime create a detached boundary layer in each array producing two symmetric fluid recirculation zones. Particles introduced into the straight channel experience two lateral lift forces due to shear gradient and wall effect when inertia is important. As particles approach the expansion, larger shear gradient lift induces larger particles to migrate laterally across streamlines and into the vortex, since the balancing wall-effect lift is no longer significant immediately after the expansion. Smaller particles are maintained in streamlines that flow out of the device because they experience less shear gradient lift--scaling with particle diameter cubed. We identify the hydrodynamic forces responsible for the trapping mechanism, determine the critical particle size for trapping and present potential biological applications in concentrating cells from complex samples using this phenomenon. [Preview Abstract] |
Monday, November 22, 2010 9:57AM - 10:10AM |
GP.00010: Anchors and rails: trapping and guiding drops in 2D R\'emi Dangla, Sungyon Lee, Charles Baroud We present a method to control the motion of drops in a wide and thin microchannel, by etching fine patterns into the channel's top surface. Such control is possible for drops that are squeezed by the channel roof, by allowing them to reduce their surface energy as they enter into a local depression. The resulting reduction in surface energy pulls a drop into the groove such that localized holes can be used as anchors for holding drops, while linear patterns can be used as rails to guide them along complex trajectories. An anchored drop can remain stationary indefinitely, as long as the velocity of the surrounding oil remains below a critical value which depends on the drop size and channel geometry. A rail pointing laterally guides drops whose size is below a critical radius which depends on physical and geometric parameters. This can be used to separate drops based on size or on their physical properties. [Preview Abstract] |
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