An advanced biological scanning electrochemical microscope (Bio-SECM) for studying individual living cells

An inverted optical microscope was customized to incorporate a constant-distance mode scanning electrochemical microscope (SECM). The system worked well with an optical, shearforce-based feedback mechanism for maintaining a constant tip-to-sample separation throughout scanning. The highly accurate distance control of the established Bio-SECM allowed novel, flexible carbon-fibre microelectrodes with appropriate vibration characteristics and significantly reduced tip diameters to be used as vibrationable SECM tips for topographical and electrochemical measurements on soft biological samples such as adherently growing fibroblasts or adrenal chromaffin cells. Visual aid offered by the optical microscope helped identifying suitable cells and supported manual prepositioning of an electrode tip next to a selected cell. Precise, non-manual positioning of the tip of the microelectrode directly above a single living cell at a distance of a fraction of a micrometre was carried out by taking advantage of topography information available from constant-distance SECM line scans. In the case of catecholamine-releasing chromaffin cells, properly placed SECM tips succeeded to detect amperometrically the release of adrenaline and noradrenaline out of single secretory vesicles upon proper stimulation.