Bashir, Rashid

Tiny silicon microchip–based high-throughput hanging drop arrays allow drug screening and geometric control.

This article describes the electrical characterization of live and heat-inactivated micro-organisms within microstructures. Electrophoretic movement of live and heat-inactivated Listeria innocua on interdigitated fingered electrodes confirmed the presence of negative charges on the live micro-organisms and demonstrated positive or neutral charges on the heat-inactivated micro-organisms. A micropore was fabricated in an oxide coated silicon diaphragm, which was placed between two chambers containing ionic buffer solutions. When the micro-organism electrophoretically traversed the pore, the background ionic current was blocked and a decrease in the current was observed. As an initial test case, negatively charged polystyrene beads, which were 2.38 μm in diameter, were electrophoretically driven across the pore. Then, Listeria innocua, suspended in tris-glycine buffer, were also moved through the pore and their electrophoretic mobility was determined. In addition, the values of mobility of the micro-organisms through the micropore were found to be about 3 orders of magnitude smaller than their mobility without the pore, which can be explained by the higher hydrostatic pressures experienced by the micro-organisms when traversing through the pore.