Non-invasive, electro-orientation-based viability assay using optically transparent electrodes for individual fission yeast cells

A non-invasive assay of cylindrical yeast cell viability based on electro-orientation (EO) in an alternating electric field was developed, in which cell viability can be determined by each cell's EO direction without the need for reagents. A cell suspension of a few microliters was sandwiched between a pair of optically transparent indium-tin-oxide (ITO) plate electrodes. Observation under a light microscope enabled easy identification of EO based on cell shape, e.g., cells were standing upright and appeared perfectly circular when oriented parallel to the electric field direction (standing position), and they were lying flat and had an elongated shape when oriented perpendicular to the field (lain-down position). The alternative EO positions of living or dead cells were dependent on the applied frequency: opposite EO positions were obtained by applying an AC voltage of 1.5 V at 10 MHz; at which point, only living cells rapidly attained a standing position, whereas dead cells were lain-down within 10 s. All the cell's EO positions agreed well with a viability assay by florescence staining. Therefore, at the single-cell level and fluorescently label-free, it was possible to simply and accurately determine whether individual cells were alive or dead based on their shape.