Abstract

Nano coding, a system for genome analysis, utilizes electro osmosis and electrophoresis to park DNA molecules in
molecular gates. Understanding how electro osmotic and electrophoretic mobilities vary due to surface charge of
the device will enable better devices to be developed for Nano coding or other genome analysis platforms. Using
a current monitoring method, the surface charge was determined for three different plasma treatments of poly
(dimethylsiloxane) (PDMS). Next, the effective electrophoretic mobility of negatively charged fluorescently labeled
microspheres was measured for a dynamic range of ionic strength solutions (0.500 – 18.00 mM). As the ionic strength
decreased, the effective electrophoretic mobility (or net mobility) decreased or moved in the opposite direction due
to electro osmosis. For all three plasma treatments, the lower ionic strength solutions (0.500 and 1.000 mM) were
dominated by electro osmosis. Electro osmosis dominated at 2.00 mM for the two highest surface charges. The
experimental net mobility was compared to theoretical considerations, utilizing the Pitts equation for electrophoretic
mobility and the Stellwagen equation for electro osmotic mobility. Both theoretical and experimental show the net
mobility decreased as the ionic strength decreased.

Keywords: Electro osmosis; Electrophoresis; Fluorescent microspheres; Low ionic strength solutions