270223 Protein Streaming Via Insulator-Based Dielectrophoresis in a Microfluidic Platform

Tuesday, October 30, 2012: 10:30 AM
Fayette (Westin )
Asuka Nakano, Fernanda Camacho-Alanis, Tzu-Chiao Chao and Alexandra Ros, Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ

Protein Streaming via Insulator-based Dielectrophoresis in a Microfluidic Platform

Asuka Nakano, Fernanda Camacho-Alanis, Tzu-Chiao Chao, Alexandra Ros

Department of Chemistry and Biochemistry, Arizona State University, Tempe AZ, 85287

Rapid and reliable separation and analysis of proteins is of great interest. This becomes especially challenging when only small sample volumes are available, concomitantly with low concentrations of proteins. Time critical situations such as surgeries and rapidly degrading samples pose additional challenges. Due to these challenges, conventional macro-scale separation techniques reach their limitations. While microfluidic devices require only pL-nL sample they offer several advantages such as speed, efficiency, and high throughput.

Here, we propose to elucidate the capability to manipulate proteins in a rapid and reliable manner with a novel migration technique, namely dielectrophoresis (DEP). We demonstrate a detailed study of various factors influencing protein DEP, employing immunoglobulin G (IgG) under DC conditions. DEP has been extensively employed as a separation, fractionation, and pre-concentration technique for large biological objects such as cells and recently for DNA. In contrast to the other existing separation techniques, DEP relies on a particle's polarizability in an inhomogeneous electric field. This additional parameter has great potential to improve separation when employed as a primary separation method as well as a component of a multi-dimensional separation. Improved separations are in demand especially when the sample becomes complex. To generate a non-uniform electric field, we specifically utilize insulator-based DEP (iDEP) where the dielectrophoretic response of proteins is provoked in a tailored microfluidic device with integrated arrays of insulating posts. Unlike DNA and cells, protein DEP behavior is not well understood; therefore our detailed study of protein DEP provides novel information to eventually optimize this protein migration method for pre-concentration and other analytical techniques.

First, we performed numerical simulations to predict protein migration behavior considering electrokinesis, protein diffusion, and DEP. With small sized (~nm) proteins, high electric field strength as well as corresponding large electric field gradient needs to be created. For this purpose, multiple post geometries were tested by numerical simulation and as a result, we found the maximum field strength of 8105 V/m and maximum ∇E2 value of 31017 V2/m3 with the triangular post geometry. Based on the calculated electric field, E, and ∇E2, we simulated the protein concentration profiles and found that the protein concentrates in streamlines between the rows of posts in the positive DEP case, whereas protein is depleted at the exact same regions for negative DEP.

Experimentally, we investigated the DEP behavior of IgG under various buffer conditions differing in pH and conductivity. We observed streaming DEP only at pH 6.5~8 with a maximum DEP streaming enrichment of 70 %. This concentration profile was in excellent qualitative agreement with numerical simulations performed with the assumption of monomeric IgG species. Furthermore, pH dependent DEP streaming is also in agreement with the numerical simulations suggesting that the variation of protein charge and electroosmotic flow influences protein DEP streaming. Additionally, we observe micelle induced negative DEP streaming for proteins, which is also in agreement with numerical simulations. This micelle formation was further confirmed by dynamic light scattering experiments. Our study thus provides valuable information to eventually improve novel protein DEP devices for separation, pre-concentration, and fractionation.

 


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