Gradient Insulator-Based Dielectrophoresis of Gold Nanoparticles.

Various forms of dielectrophoresis and higher order electrokinetic effects are being increasingly investigated and used to precisely and accurately manipulate micro and nanoparticles within microfluidic devices. The types of particles span ∼10 nm to hundreds of microns in diameter and are composed of minerals, polymers, biological materials, and complex mixtures. Some studies focused on the selective isolation and concentration of purified particles countering negative dielectrophoretic forces against flow and electrophoretic effects. Similar studies are presented here examining the behaviors of small inorganic particles (10 nm diameter) where their collective actions are inconsistent with negative dielectrophoretic effects and were consistent overall with positive dielectrophoresis (DEP). Positive DEP can account for some of the observed phenomena, particularly the deflection of large particle aggregates, which are rapidly accelerated through microchannel constrictions and then pulled back toward the constrictions against the direction of electroosmotic flow. Nevertheless, the dynamic complexity of the observed nanoparticle structures suggests that a myriad of electrostatic and possibly hydrodynamic forces, including both particle-particle and particle-device interactions, may be involved.