AC and DC Protein Streaming and Trapping with Insulator-Based Dielectrophoretic Devices

 Microfluidic devices offer several experimental advantages over macroscale methods such as speed, efficiency, and high throughput giving them great potential for rapid and reliable separation and analysis of proteins. Here we propose to manipulate proteins rapidly and reliably with a novel migration technique utilizing dielectrophoresis (DEP). Our study demonstrates protein DEP responses under DC and AC conditions using a variety of insulator-based DEP (iDEP) devices and proteins including immunoglobulin G (IgG), lysozyme, and β-galactosidase. Even though DEP has been extensively employed as a separation, fractionation, and pre-concentration technique for large biological objects such as cells and DNA, protein DEP behavior is not well understood. Our detailed study of protein DEP provides novel information for future optimization of this protein migration method for pre-concentration and other analytical techniques. 

First, we performed numerical simulations to estimate electric field strength (E) as well as electric field gradients, ∇E² within our microdevices. Based on the calculated E and ∇E², we simulated protein concentration profiles considering electrokinesis, protein diffusion, and DEP to predict protein migration behavior. Simulation results indicated that under both positive and negative DEP conditions, proteins concentrated as streamlines between the post arrays. With IgG, we experimentally observed protein streaming behavior due to positive DEP with a maximum concentration of 70 %. This concentration profile was in excellent qualitative agreement with numerical simulations for a monomeric IgG species. Moreover, using improved nanoconstriction devices, we successfully trapped proteins under both AC and DC conditions. Our study thus provides valuable information to develop novel protein iDEP devices for separation, pre-concentration, and fractionation.