Dielectrophoretic Manipulation and Controlled Release of Surfactant Based Micelles

Lipid and surfactant based biocolloids have been of increasing interest as delivery systems for controlled release, targeting, or medical diagnostics via AC-electrokinetic and other  techniques.  In this work, we examine the behavior of surfactant based micelles under dielectrophoresis (DEP) as a means to rapidly assemble micellar complexes with controlled release of varied encapsulatess.  The dynamic response of sodium tetradecyl sulfate (STS) and sodium dodecyl sulfate (SDS) micelles, each 3-5 nm in diameter, is accomplished through single-molecule resolution spectroscopy, namely fluorescence correlation spectroscopy (FCS).  We focus specifically on the AC-induced concentration changes of micelles due to applied field of AC-field frequencies of 5 kHz – 20 MHz at an amplitude of 20 V (peak-to-peak).  We observe a strong dependence of micelle concentration on ac-field frequency in the region of high field strength.  Surprisingly, we also observe an AC-induced dissociation of the micelle structure, resulting in the release of the encapsulated chemicals at low AC-field frequencies (< 10 kHz).  In addition, the micellar dissociation is found to be linked specifically to the surface charge of the interior encapsulate.