Abstract
We introduce a method for improved dielectrophoretic (DEP) discrimination and separation of viable and nonviable yeast cells. Due to the higher cell wall permeability of nonviable yeast cells compared with their viable counterpart, the cross-linking agent glutaraldehyde (GLT) is shown to selectively cross-link nonviable cells to a much greater extent than viable yeast. The DEP crossover frequency (cof) of both viable and nonviable yeast cells was measured over a large range of buffer conductivities (22 muScm-400 muScm) in order to study this effect. The results indicate that due to selective nonviable cell cross-linking, GLT modifies the DEP cof of nonviable cells, while viable cell cof remains relatively unaffected. To investigate this in more detail, a dual-shelled oblate spheroid model was evoked and fitted to the cof data to study cell electrical properties. GLT treatment is shown to minimize ion leakage out of the nonviable yeast cells by minimizing changes in cytoplasm conductivity over a large range of ionic concentrations. This effect is only observable in nonviable cells where GLT treatment serves to stabilize the cell cytoplasm conductivity over a large range of buffer conductivity and allow for much greater differences between viable and nonviable cell cofs. As such, by taking advantage of differences in cell wall permeability GLT magnifies the effect DEP has on the field induced separation of viable and nonviable yeasts.