Material-selective separation of mixed microparticles via insulator-based dielectrophoresis.

Insulator-based dielectrophoresis (iDEP) has become a powerful tool for biomicrofluidic separation and analysis because it is capable to selectively separate biological particle systems according to properties like size, material, and shape. However, it has rarely been used to solve challenging separation problems involving nonbiological particles, namely, for systems that are prone to particle agglomeration. Here, we demonstrate material-selective separation of nonbiological systems, i.e., polystyrene and gold-coated polystyrene particles of two different sizes, using iDEP at high accuracy. For this purpose, we present a method to generate fluorescent gold-coated particles. We further introduce a method to reduce the static backpressure that builds up between in- and outlet reservoir due to electroosmotic flow. Moreover, we found that particle agglomeration makes their separation impossible when conventional iDEP routines are applied. Therefore, two solutions to reduce particle agglomeration are presented: A combination of AC and DC potentials and adjustment of pH and conductivity of the suspending medium. Both approaches allow separating particles under challenging conditions such as initially low absolute particle zeta potentials and high particle concentrations. Since those conditions can also be present in biological iDEP separation processes, the results are of general value for biological and nonbiological iDEP operations.