Characterization of particle capture in a sawtooth patterned insulating electrokinetic microfluidic device

Abstract

Here we present a scheme to separate particles according to their characteristic physical properties, including size, charge, polarizability, deformability, surface charge mobility, dielectric features, and local capacitance. Separation is accomplished using a microdevice based on direct current insulator gradient dielectrophoresis that can isolate and concentrate multiple analytes simultaneously at different positions. The device is dependent upon dielectrophoretic and electrokinetic forces incorporating a global longitudinal direct current field as well as using shaped insulating features within the channel to induce local gradients. This design allows for the production of strong local field gradients along a global field causing particles to enter, initially transported through the channel by electrophoresis and electroosmosis (electrokinetics), and to be isolated via repulsive dielectrophoretic forces that are proportional to an exponent of the field gradient. Sulfate-capped polystyrene nano and microparticles (20, 200 nm, and 1 μm) were used as probes to demonstrate the influence of channel geometry and applied longitudinal field on separation behavior. These results are consistent with models using similar channel geometry and indicate that specific particulate species can be isolated within a distinct portion of the device, whereas concentrating particles by factors from 10(3) to 10(6).

Refinement of insulator-based dielectrophoresis

“…This arc structure has been observed in many experimental systems and is demonstrated computationally (Figures 5A, 5B, 5C, & 5D). 1, 3, 8–11,42, 45, 49, 50 The net result is consistent with current experimental systems, where small collections of analytes are observed close to the point of greatest constriction of wide gates and full arcs form when complete trapping across the lateral dimension occurs. For a single particle population, some particles will trap on these wide gates, while other will continue on, which distributes that single population throughout the device.…”

“…The triangular insulator is representative of diamonds, sawteeth, and triangles used for insulators. 11, 23, 28, 31, 42, 43, 45 Along the centerline, the value for the gradient of the $\nabla │\stackrel{\rightharpoonup }{E}{│}^2$ is for the 34.10 μm gate is approximated to be 3.2×10 16 V 2 /m 3 , which is the highest value of any of the insulator shapes examined. Particles will travel along the field line by EK forces in the absence of a significant gradient.…”

“…The current channel measurements have been used for the manipulation and separation of several analytes including: polystyrene spheres, red blood cells, different serotypes of Escherichia coli , and different strains of Staphylococcus epidermidis . 1, 8, 11, 42 The channels modeled ranged in length from 7.5–12 mm (only the Inverse 20× Curve channels were on the upper end of this). A 500 V potential was applied so that the inlet wall was a ground and the outlet wall carried the potential (Figure 2A).…”

“…The assessment here focuses on the constriction design, which is universal to all iDEP systems. 29 Examples of insulator shapes currently utilized include rectangle 14, 31, 41 , triangle 25–27, 31 , sawtooth 11, 23, 42, 43 , circular posts 2, 10, 11, 27, 28, 35, 44 , and diamond posts. 28, 45, 46 Trapping DEP leads to the isolation and concentration of analytes near the constriction points in the microchannels.…”

“…For the purpose of high resolution separations, several factors come into play; including high values for the electric field and gradient 12 and the induction of all particles of an identical population to traverse the longitudinal axis in a similar fashion where the electric field strength and gradient intensity achieve separatory differentials (whether trapping, streaming (multi-outlet), or stochastic-based and chromatography-like elution-based strategies). 10, 11, 42, 43, 51–55 The identical or at least similar (accounting for diffusion and dispersion) movement of all particles of a homogeneous population is a core tenet of separations science. The manipulation of analytes by DEP is possible because each analyte has unique properties reflected by their electrophoretic ( ${\mu }_{EP}$) and dielectrophoretic ( ${\mu }_{\mathit{\text{DEP}}}$) mobilities.…”