Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session X14: Micro and Nano Fluid Mechanics |
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Sponsoring Units: DFD Chair: Boyd Edwards, West Virginia University Room: 315 |
Thursday, March 19, 2009 2:30PM - 2:42PM |
X14.00001: The dynamical origin of the zeta potential Patrick Tabeling By using evanescent waves, we study equilibrium and dynamical properties of liquid-solid interfaces in the Debye layer for hydrophilic and hydrophobic surfaces. We measure velocity profiles and nanotracer concentration and diffusion profiles between 20 and 300 nm from the walls in pressure-driven and electroosmotic flows. We extract electrostatic and zeta potentials and determine hydrodynamic slip lengths with 10 nm accuracy. The spectacular amplification of the zeta potential resulting from hydrodynamic slippag allows to clarify for the first time the dynamic origin of this potential. [Preview Abstract] |
Thursday, March 19, 2009 2:42PM - 2:54PM |
X14.00002: Radiofrequency Nanoelectrolytic Debye-Layer Transistor Jean-Luc Fraikin, Michael Requa, Michael Stanton, Andrew Cleland A voltage-biased metal immersed in an aqueous electrolyte attracts ions from the solution, causing the accumulation of a diffuse layer of charge close to its surface. This layer is called the Debye-Huckel layer, or double layer. For a non-reactive electrode, the electric double-layer (EDL) presents a capacitive electrical impedance, which depends non-linearly on the voltage applied across it. We present a novel transistor whose transduction element is the EDL capacitance, which allows electronic gating of a 50 MHz signal at frequencies close to 1 MHz. The transistor comprises three terminals: a pair of nanofabricated interdigitated electrodes (IDEs) embedded in an electrolyte-filled microfluidic channel, and a third, gating Ag/AgCl electrode in the same fluid volume. We demonstrate direct gating of the transistor with the Debye layer, and make use of the device to measure the voltage dependence of the EDL capacitance over a broad range of electrode bias. [Preview Abstract] |
Thursday, March 19, 2009 2:54PM - 3:06PM |
X14.00003: Simulation of Steady-State Non-Equilibrium Ion Distributions Within a Finite-length Nanofluidic Channel William Booth, Jarrod Schiffbauer, Josh Fernandez, Kathleen Kelley, Aaron Timperman, Boyd Edwards Steady-state non-equilibrium distributions of two species of mono-valent ions near and within a charged 2D nanofluidic channel have been examined with and without electroosmotic flow. Large reservoirs are connected by the nanofluidic channel to simulate bulk conditions. Far-from-equilibrium applied voltages create a charge polarization across the nanochannel when the Debye length is comparable to the channel width. Depletion zones of each ion species are observed. [Preview Abstract] |
Thursday, March 19, 2009 3:06PM - 3:18PM |
X14.00004: DEP Force Spectroscopy Jingyu Wang, Steven M.T. Wei, Joseph Junio, H.D. Ou-Yang We report measurement of the frequency-dependent dielectrophoretic forces imparted on individual colloid particles in an aqueous suspension. The motion of suspended particles relative to the solvent resulting from polarization forces due to an inhomogeneous electric field is known as the dielectrophoretic force (DEP). In the case of colloidal particles, the Claussius-Mossotti (CM) function containing the frequency dependence of the dielectric behavior of the particle relative to the suspending fluid dictates the direction and magnitude of the resulting DEP force. The magnitude of this force approaches zero as the frequency approaches the point of cross-over to switch the direction of the force. Using optical tweezers as force sensor we have successfully characterized the frequency dependent DEP force with a spatial resolution in the micron range and a force resolution of a fraction of 1pN. To achieve this, we used an AM modulation scheme to administer the oscillating electric field, so that we could monitor the phase and amplitude of the displacement of the particle while it was held by the optical tweezers and acted on by the DEP force. The optical tweezers based DEP force spectroscopy presents a way to understand the fundamental parameters at the microscopic level. [Preview Abstract] |
Thursday, March 19, 2009 3:18PM - 3:30PM |
X14.00005: A New Fourier Model of Traveling Wave Electrophoresis Robert Correll, James Eakins, James Vopal, Boyd Edwards Traveling-wave electrophoresis is a new method of separating charged analytes using a series of interlaced electrodes with time-varying electric potentials along a microchannel. It potentially offers several potential advantages over conventional electrophoretic devices, including increased separation efficiency and ease of scalability. A better description of the underlying mathematics is required in order to fully optimize this promising technology. As such, a new Fourier model of the electric potential inside the channel is introduced, along with preliminary computational results. This new representation allows for greatly reduced computation time and greater accuracy. Similarities and differences with other models are highlighted, as well as the dependence of the potential on the electrode and channel geometries. The movement of charged particles in response to the potential is examined, with several critical thresholds highlighted. [Preview Abstract] |
Thursday, March 19, 2009 3:30PM - 3:42PM |
X14.00006: Traveling-wave electrophoresis for microfluidic separations Boyd Edwards, Aaron Timperman, Lloyd Carroll, Kyoo Jo, Jon Mease, Jarrod Schiffbauer Models and microfluidic experiments are presented of an electrophoretic separation technique in which charged particles whose mobilities exceed a tunable threshold are trapped between the crests of a longitudinal electric wave traveling through a stationary viscous fluid. The wave is created by applying periodic potentials to electrode arrays above and below a microchannel. Predicted average velocities agree with experiments and feature chaotic attractors for intermediate mobilities. [Preview Abstract] |
Thursday, March 19, 2009 3:42PM - 3:54PM |
X14.00007: Trigonometric Model for Traveling Wave Electrophoresis James Vopal, Boyd Edwards The motion of ions in a trigonometric spatio-temporal potential in a fluidic microchannel is investigated. Computer simulations are performed for ions of different mobilities to predict the ionic trajectories and average velocities. In many instances, plotting the average velocity verses mobility results in a Devil's staircase. When Devil's staircases are seen, no chaotic behavior is present. When the average velocity verses mobility does not result in a Devil's staircase, chaotic trajectories can be found. [Preview Abstract] |
Thursday, March 19, 2009 3:54PM - 4:06PM |
X14.00008: Electrokinetic interaction between a charged cylindrical particle and a charged planer surface Dolfred Vijay Fernandes, Sangmo Kang, Yong Kweon Suh Electrophoretic motion of a charged particle under an electric field applied parallel to the planer surface has been studied numerically. Effect of electric double layer (EDL) interaction between the particle and the surface on the electrophoretic motion is the main focus of the study. Thick EDL around the particle and on the surface is obtained by solving Poisson-Nernst-Planck (PNP) equations on a hybrid grid system. A Lagrange type cylindrical grid attached to the particle can move freely on Euler type Cartesian grid. Second order accurate bilinear-interpolation scheme is used at the intersection of Lagrange-Euler grid. The linear and rotational motion of particle in the electroosmotically driven fluid is obtain by balancing EDL interaction force, gravitational force, electrostatic force and hydrodynamic force. The fluid flow along the surface and around the particle is computed by solving Stokes equations. [Preview Abstract] |
Thursday, March 19, 2009 4:06PM - 4:18PM |
X14.00009: Ac electroosmotic flows above coplanar electrodes Yong Kweon Suh Interactive numerical method has been proposed to calculate the ac electroosmotic flows above a pair of coplanar electrodes. The thin electrical triple layer (ETL) has been modeled by an asymptotic theory developed by the authors. The model corresponds to a simple dynamic equation for the surface charge density representing the integrated charge over the inner layer. Interactive calculation of the dynamic equation and the Laplace equation for several periods of ac frequency then yielded steady-state distribution of potential and the potential drop across the Stern and inner layers. The Smoluchowski's slip velocity was then determined from those two set of data and used as the boundary condition for the calculation of the Stokes' flow above the electrodes. We have shown that our solutions compared well with the experimental data reported in the literature. We investigated the effect of various parameters on the slip velocity distribution, such as the ac frequency, the electrode length, the effective Stern-layer thickness and the adsorption coefficients. [Preview Abstract] |
Thursday, March 19, 2009 4:18PM - 4:30PM |
X14.00010: Detection and electrokinetic trapping of single fluorescent molecules in fused silica nanochannels Brian Canfield, Xiaoxuan Li, William Hofmeister, Lloyd M. Davis We describe experimental detection and electrokinetic trapping of single, fluorescently-labeled proteins confined within $\sim $100 nm fluidic channels fabricated in fused silica. Though difficult to fabricate, the fused silica environment yields lower autofluorescence than borosilicate glass, which is especially advantageous given the low light level from single molecules. The molecules are dispersed in a buffer solution at ultralow concentration ($\sim $10$^{-12}$ M) to provide single-molecule occupancy of the sub-femtoliter probe volume within the nanochannel. Fluorescence is excited and collected in a custom-built confocal microscope, using two temporally interleaved beams from a modelocked dye laser focused to adjacent spots along the nanochannel. Detection is accomplished with custom single-photon avalanche diodes for time-resolved single-photon counting, and by using this time stamp information, a field-programmable gate array circuit board controls the electrokinetic trapping by modulating an applied voltage. Fluorescence correlation spectroscopy is also used to monitor the transport of molecules along the nanochannel. Electrokinetic transport can thus be characterized from changes in the autocorrelation function with voltage modulation. [Preview Abstract] |
Thursday, March 19, 2009 4:30PM - 4:42PM |
X14.00011: Microfluidic device for the electrokinetic manipulation of single molecules Jason King, Lloyd Davis, Brian Canfield, William Hofmeister, Philip Sampson We are developing a microfluidic device for three-dimensional electrokinetic manipulation of single fluorescent molecules in solution. The device consists of electrode pairs deposited onto glass cover slips via UV microlithography and ionic sputtering. By positioning two such electrode pairs in a tetrahedral configuration separated by 100 microns and applying appropriate digitally-controlled voltages to each, the apparatus generates an electric field of selected directionality in the central bounded region. Proof of concept is demonstrated by controlling the motion of micron-size latex beads, visualized with an EM-CCD camera. By use of a double Mach-Zehnder interferometer configuration, 40 fs Ti:Sapphire laser pulses (repetition rate 76 MHz) are split into four temporally interleaved pulses (effective rate 304 MHz), which are then focused to the vertices of a tetrahedron (approximately one micron per side) within the central electrode region to generate two-photon-excited fluorescence from single molecules. The time stamp data from this four-focus probe, collected with a custom fast-timing single-photon avalanche diode, enables characterization of particle motion through fluorescence cross-correlation spectroscopy. [Preview Abstract] |
Thursday, March 19, 2009 4:42PM - 4:54PM |
X14.00012: Microfluidic Channels under Magnetohydrodynamic (MHD) Convection Yogendra M. Panta, Hyun W. Kim, Shizhi Qian Magnetohydrodynamic (MHD) effects have been widely known since many years. MHD effects are used to propel, stir, and pump fluids in various fluid applications especially in the field of microfluidics and Lab On a Chip (LOC) technology. Orthogonally aligned electric flux density and magnetic flux density were applied to straight and torroidal micro-channels both aligned perpendicular to the desired direction of fluid flow. Microfluidic MHD channels in straight and torroidal shapes were fabricated from a thin brass sheet sandwiched between two polycarbonate sheets patterned with two platinum electrodes in the channel walls from inside. When a potential difference of low magnitude ($\sim $ 1 mV) is applied across the electrodes, a current density J transmitted through the electrolyte solution results. In the presence of a magnetic field B, the orthogonal interaction between the resulting current density J and the magnetic field B induces Lorentz forces F (=J$\times $B) which induce and drive fluid motion in the channel. This effect was applied to propel and pump the fluid in presence of a current carrying species both in a straight and torroidal micro-channels. Flow velocities were obtained linearly increasing with the higher magnetic flux densities. A drop of dye was placed into the solution to trace the path of moving fluid under MHD convection. [Preview Abstract] |
Thursday, March 19, 2009 4:54PM - 5:06PM |
X14.00013: Cell and Colloidal Substrates for Dielectrophoretic Microfluidic Immunoassays Jill Mazur, Zachary Gagnon, Hsueh-Chia Chang Dielectrophoresis (DEP) is a term commonly used to describe the field induced polarization and translational motion of a polarizable particle in a non-uniform AC field. The frequency at which the induced particle dipole goes to zero, known as the crossover frequency (cof), is highly dependent on the surface conductance of the particle. We have shown previously that DNA hybridization on the surface of a 100 nm functionalized silica particle leads to detectable surface conduction changes which make it possible to detect DNA hybridization reactions by simply measuring changes in particle suspension cof. In this work we present a similar detection scheme using novel colloidal and cell substrates as dielectrophoretic immunosensors. Aminated cell or nanocolloid surfaces are subjected to a polymer coating glutaraldehyde treatment followed by antibody coupling reaction for immunoassay based detection. By varying the polymer coating thickness on the colloid or cell surface we demonstrate the ability to tune, stabilize the cell and colloid cof, and minimized non-specific adsorption of proteins. As such, a library of cof labeled colloids and cells are created and used for multiple antigen analysis. By measuring the colloid and cell specific DEP cof prior to and after antibody-antigen interaction we demonstrate the ability to perform rapid label free protein detection within a microfluidic device. [Preview Abstract] |
Thursday, March 19, 2009 5:06PM - 5:18PM |
X14.00014: AC Electrokinetic Cell Separation on a Microfluidic Device Zachary Gagnon, Hsueh-Chia Chang Rapid cell separation and collection is demonstrated through the integration of electrokinetic pumps, dielectrophoretic (DEP) traps and field driven valves into a well designed microfluidic channel loop. We present the ground-up design and analysis of this fully functional microfluidic device for the rapid separation and collection of live and dead yeast cells and malaria red blood cells (RBCs) at low concentrations. DEP cell sorting and concentration schemes are based on the exploitation of cell specific DEP crossover frequencies (cof's). A rigorous DEP study of yeast and RBCs is presented and used to determine optimal conditions for cell separation. By utilizing a glutaraldehyde crosslinking cell fixation reaction that is sensitive to cell membrane protein concentration, we demonstrate the ability to further amplify these differences between healthy and unhealthy cells as well as stabilize their DEP cof's. Pumping is achieved with a new type of electrokinetic flow, AC electrothermal electro-osmosis (ETEO) and is shown to scale inversely with the field induced debye length and drive fluid velocities in excess of 6 mm/sec. The well characterized electrokinetic phenomena are integrated into a microchannel loop with a specifically designed electrode field penetration length for low concentration cell separation and concentration. [Preview Abstract] |
Thursday, March 19, 2009 5:18PM - 5:30PM |
X14.00015: Anomalous analyte dispersion at microchannel-nanocapillary membrane interfaces Jarrod Schiffbauer, Kathleen Kelly, Will Booth, Josh Fernandez, Aaron Timperman, Boyd Edwards The dispersion of a plug-like distribution of negatively charged fluorescent dye molecules inside a microchannel is studied by numerical analysis of a time-series of epifluorescence microscope images. The concentration is accomplished using a nanocapillary membrane (NCM) --based concentration device. Dispersion of the analyte after concentration is complete, i.e. after the applied voltage is removed, is of considerable technical interest as a limiting factor in the functionality of lab-on-a-chip concentration devices. Subsequent band-broadening is inconsistent with Taylor dispersion and is shown here to be influenced by the presence of charge-separation between the concentrated analyte and background buffer ions. [Preview Abstract] |
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