The potential energy surfaces generated by microelectrodes of polynomial and interdigitated castellated geometry have been calculated for particles experiencing both positive and negative dielectrophoretic forces. The resulting forms of particle collection at these electrodes are governed by the locations of the potential energy wells, and the theoretical predictions of the modes of collection for particles experiencing positive and negative dielectrophoretic forces are verified using mixtures of viable and non-viable yeast cells, as well as of bacteria and blood cells. An important result for the interdigitated electrodes is the finding that particles trapped in potential energy wells under the action of negative dielectrophoresis can be more easily removed from the electrode structure (e.g. by fluid flow or gravitational forces) than those trapped under positive dielectrophoresis. This was verified for mixtures of bacteria and blood cells, viable and non-viable yeast cells.