Dielectrophoretic dots: development of hardware for realtime cellular assessment

Dielectrophoresis (DEP), the motion of polarisable particles in non-uniform fields, has already been shown to be effective for the determination of the dielectric properties of cells for electrophysiological investigation. Applications have been demonstrated from drug screening to extending our understanding of cancer biology. However conventional methods for dielectrophoretic analysis are not well suited for large numbers of parallel experiments, due to the complex nature of electrode fabrication, the very low effective volumes (of the order of nanolitres) in which DEP is effective, and the difficulty in making simple observations of many cells (which are typically microscope-based). In this proposal, a new system of DEP analysis will be constructed using parallel arrays of electrodes (the so-called dot electrodes ). Electrode technology recently developed at the University of Surrey has produced a novel electrode structure for DEP, for which a patent has recently been filed. Whereas previous DEP studies have used electric fields generated by planar (effectively 2D) electrodes etched from gold across the surface of a microscope slide, the new technology uses parallel-plane dot electrode structures to generate simple-to-interpret DEP data rapidly (of the order of 10-20 seconds). The system operates as follows. The dielectrophoretic dot chambers are filled with cell suspension, followed by the drug candidate. An array of dots will be energized by perhaps 20 frequencies, one to each dot, so that the whole spectrum can be obtained simultaneously. The dots will be of sufficient size and spread to ensure the whole array is visible simultaneously using the microscope. Upon the application of the electric field, positive dielectrophoresis removes the cells from the bulk liquid and reduces light scattering, whereas negative dielectrophoresis focuses particles in the middle of the dot and increases light scattering. A high-resolution digital camera uses image-processing algorithms to analyse the change in cell distribution, at a specific time after the application of the field, and hence determine the dielectrophoresis spectrum. This novel approach will enable observation of much more rapid cellular phenomena; in this project the equipment will be demonstrated by observation of cancer drug action and in the onset of cell toxicity, and the onset of apoptosis. All three of these represent important aspects of the study of pharmacology and toxicology, for which fields this project has potential to impact significantly.