In situ observations of submicron fluorescent tracers suspended in high ionic strength media sealed in a confined geometry are combined with 3-D simulations in order to provide a better understanding of the synergism between dielectrophoresis and electrothermal flows that cause rapid particle transport and trapping on the surface of planar quadrupolar microelectrodes. The influence of electrode design on the microfluidic patterns and observed particle collection is examined by employing two different types of microelectrodes in the experiments. The potential use of quadrupolar microelectrodes as means for achieving accelerated sampling and signal amplification in future surface based biosensor devices is illustrated with an experiment involving stable capture of antigen-coated polystyrene particles on the surface of an antibody-functionalized microelectrode array.