(415f) Dielectrophoresis and AC-Field Induced Encapsulate Release of Micelles in Aqueous Suspensions

Recently, lipid based biocolloids, such as micelles and liposomes, have been of increasing interest as drug delivery systems for controlled release, specific cell targeting, or medical diagnostics via advanced electrokinetic and microfluidic techniques. In this work, we examine dielectrophoresis (DEP) of complex bio-nanocolloids, where nanoparticles can be effectively and rapidly manipulated and assembled in suspensions by the use of an AC-electric field. The dynamic response of micelles, of 3-5 nm in diameter, to applied AC-electric fields is examined through the use of fluorescence correlation spectroscopy (FCS) at a single-molecule resolution. We focus on the AC-field induced transport of sodium dodecyl sulfate (SDS) micelles tagged with various fluorescent encapsulates in aqueous media. The AC-electric field induced concentration changes and DEP mobility are accurately determined over a broad range of AC-field frequencies (5 kHz ? 20 MHz) at amplitude of 10 V_pp. We observe a strong AC-frequency dependence of micelle concentration between two microelectrodes, from which the DEP crossover frequency is determined. The crossover frequency, or the point at which the nanocolloid DEP response switches between positive and negative DEP, is observed for micelles and nanocolloids of 10 nm for the first time. Surprisingly, we also observe an AC-field induced dissociation of the micelle structure and a resulting release of fluorescent encapsulates at a characteristic low AC-field frequency of ~1-10 kHz, where the dissociation has been found to be dependent on the surface charge of the interior encapsulate. Manipulation and induced release of complex nanostructures could have potential applications for controlled drug release and lab-on-a-chip technologies.