Photocurrent\nPolarity-Switchable Imaging of Single\nLiving Cells by Light-Addressable Electrochemical Sensor

The light-addressable electrochemical sensor (LAES) is\na powerful\ntool for single-cell imaging due to its label-free and probe-free\nadvantages. In this work, we report a photocurrent polarity-switchable\nLAES using a single-phase photoelectrode of a BiFeO<sub>3</sub> thin\nfilm for living cell imaging. The proposed BiFeO<sub>3</sub> could\nshow both p- and n-type photocurrent behavior by simply altering the\nexternal bias voltage. LAES imaging of the same individual MCF-7 cells\nwas performed in anodic and cathodic modes. Decreases in both photocurrents\nwere observed due to the hindering effect of the adherent cells on\nlocal photoinduced Faraday currents. Furthermore, the dynamic photocurrent\nchanges on cells after trypsin treatment were imaged and studied at\nanode and cathode polarities. Both polarities showed an increase in\nlocal photocurrents on cells as the cell–substrate junction\nweakened, and this change displayed heterogeneous characteristics.\nThis is the first time that LAES cell imaging was achieved in a p-type\nmode. Meanwhile, our photocurrent polarity-switchable imaging approach\novercomes the limitations of conventional photoelectrodes, which have\nbeen confined to single-polarity operation. We believe this work has\nthe potential to significantly broaden the application scope of LAES\nin single-cell visualization and analysis, offering great insights\ninto cellular behavior and function.