(331e) Dielectrophoresis and AC-Field Induced Encapsulate Release of Micelles in Aqueous Suspensions

Biocolloids, such as micelles and liposomes, have been of increasing interest as drug delivery systems for controlled release and specific cell targeting via advanced electrokinetic and microfluidic techniques, such as dielectrophoresis (DEP), where colloid particles can be effectively and rapidly manipulated and assembled in suspensions by the use of an AC-electric field. In this work, we examine the dynamic responses of micelles, of 3-5 nm in diameter, to applied AC-electric fields by using 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 probes and molecular encapsulates in aqueous media. Micelle assembly concentration and DEP mobility of SDS micelles are accurately examined over a broad range of AC-field frequency (1 KHz -10 MHz) and amplitude (100mV -20V). We observe a strong AC-frequency dependence of micelle concentration between two microelectrodes, from which the DEP crossover frequency switching between the positive and negative DEP response for nanocolloids of less than 10 nm is determined for the first time. Surprisingly, we also observe the AC-field induced dissociation of the micelle structure and the resultant release of fluorescent encapsulates at a characteristic low AC-field frequency of ~1-10 kHz; the dissociation frequency can be tuned by encapsulated molecules with a strong dependence of their surface conductivity, which could have a potential application for controlled drug release by AC-electric fields.