Orthogonal optical force separation simulation of particle and molecular species mixtures under direct current electroosmotic driven flow for applications in biological sample preparation

Abstract

Presented here are the results from numerical simulations applying optical forces orthogonally to electroosmotically induced flow containing both molecular species and particles. Simulations were conducted using COMSOL v4.2a Multiphysics® software including the particle tracking module. The study addresses the application of optical forces to selectively remove particulates from a mixed sample stream that also includes molecular species in a pinched flow microfluidic device. This study explores the optimization of microfluidic cell geometry, magnitude of the applied direct current electric field, EOF rate, diffusion, and magnitude of the applied optical forces. The optimized equilibrium of these various contributing factors aids in the development of experimental conditions and geometry for future experimentation as well as directing experimental expectations, such as diffusional losses, separation resolution, and percent yield. The result of this work generated an optimized geometry with flow conditions leading to negligible diffusional losses of the molecular species while also being able to produce particle removal at near 100% levels. An analytical device, such as the one described herein with the capability to separate particulate and molecular species in a continuous, high-throughput fashion would be valuable by minimizing sample preparation and integrating gross sample collection seamlessly into traditional analytical detection methods.

Pico-Force Optical Exchange (pico-FOX): Utilizing Optical Forces Applied to an Orthogonal Electroosmotic Flow for Particulate Enrichment from Mixed Sample Streams

“…For a sample collected from the second outlet reservoir, the 6 μm particles comprised 87% of the total number of particles, while for a sample collected from the third outlet; the 10 μm particles comprised 84% of the total number of particles. For both 6 and 10 μm polystyrene, enrichment of >80% was observed which is in general agreement with previously published results of COMSOL modeling of the same geometry that predicted 100% separation efficiency for the same particle types . The main source of cross-contamination in the size-based separation was not directly determined.…”

“…The experimental behavior of the sized-based separation of the 6 and 10 μm polystyrene particles from the food dye correlated with the predicted behavior . The composite image of the separation region showed the trajectories of the various sample components (Figure ).…”

“…The use of an external electric field was also beneficial as a means of pulseless pumping via EOF. Modeling and optimization of the pico-FOX system, its separation potential, and theoretical underpinnings have been previously described and formed the basis for this experimental investigation …”

“…This recovery efficiency can be visualized, qualitatively, by examining the outlet ports of the microfluidic cell where the dye was observed to be primarily localized in the first outlet port (Figure ). Even if every effort was made to optimize the microfluidic chip for dye collection, while disregarding particle separation, the nature of the platform results in a loss of 2.5% of the original dye concentration …”

“…Modeling and optimization of the pico-FOX system, its separation potential, and theoretical underpinnings have been previously described and formed the basis for this experimental investigation. 14 Two experimental separation modes were explored: (1) separation and refinement of different sized particles from a molecular species (Figure 2A), as well as (2) the separation of multiple material types of particles of the same size from a molecular species on the basis of their various refractive indices and electrophoretic mobilities (Figure 2B). In the first case, the mixed sample of 6 and 10 μm polystyrene particles and commercial food dye was pinched by the EOF flow from the other two inlets.…”