D T Leighton | PubMed Health

PubMed2001

Dispersion reduction in pressure-driven flow through microetched channels.

Fluid is often moved about microetched channels in lab-on-a-chip applications using electrokinetic flows (electrophoresis or electroosmosis) rather than pressure-driven flows because the latter result in large Taylor dispersion. However, small pressure gradients may arise unintentionally in such systems due to a mismatch in electroosmotic flow rates or hydrostatic pressure differentials along the microetched channel. Under laminar flow conditions, Doshi et al. (Chem. Eng. Sci. 1978, 33, 795-804) have shown that for a channel with rectangular cross-section of width W and depth d, longitudinal diffusivities can attain values as large as approximately 8 K0 for small values of the aspect ratio d/W, where K0 is the value of the longitudinal diffusivity obtained by ignoring all variations across the channel. Microchannels in lab-on-a-chip geometries are often not rectangular in cross-section. Isotropic etching techniques, for example, lead to channels with quarter-circular ends. In this paper we examine the effect of this geometry on the magnitude of longitudinal dispersivity for pressure-driven flows and also investigate modifications to this design which may minimize such dispersion. Optimal channel profiles are shown to lead to dispersivities approaching K0, the theoretical minimum, for small values of d/W.

Journal Article↗

PubMed1998

Binary oscillatory cross-flow electrophoresis: theory and experiments.

In this article a novel electrophoretic separation technique, Binary Oscillatory Cross-flow Electrophoresis (BOCE), is described. The technique utilizes the interaction of an oscillatory electric field and a transverse oscillatory shear flow to create an active binary filter for the separation of charged protein species. An oscillatory electric field is applied across the narrow gap of a rectangular channel inducing a periodic motion of charged protein species. The amplitude of this motion depends on the dimensionless electrophoretic mobility, alpha = Eomu/omegad, where Eo is the amplitude of the electric field oscillations, mu is the dimensional mobility, omega is the angular frequency of oscillation, and d is the channel gap width. An oscillatory shear flow of the form ū = Deltaxomega(beta + cos(2omegat)) where beta is the fraction of steady flow and Deltax is the tidal displacement, is induced along the length of the channel resulting in the separation of species with different mobilities. An analytic model is presented that predicts the induced convective velocity of solute species as a function of alpha and beta in the absence of diffusion. Numerical simulations including diffusion support these predictions, and determine the time history of the concentration profiles in a separation cell and connecting reservoirs. In experiments using a model protein system including bovine serum albumen (BSA) and bovine hemoglobin (BHb), solute throughputs of 37 mg/h of 92% pure BSA have been observed in a small separation cell with a volume of 3 mL. These results are in close agreement with theoretical predictions.

Animals↗