Single-cell scanning photoelectrochemical microscopy using micro-optical-ring electrodes.

Microelectrodes as analytical sensing tools have gained immense popularity in a wide range of applications, ranging from probe design advancement to single live cell imaging. Micro-optical-ring electrodes (MOREs) are micro-scale ring-electrodes with an optical fiber core, that enables the MORE to conduct an optical signal while performing electrochemistry. Herein, we present a user-friendly and cost-effective method to fabricate MOREs for scanning photoelectrochemical microscopy (SPECM) applications. MOREs were characterized by electrochemistry, numerical modelling, and scanning electron microscopy (SEM), ensuring reproducibility in terms of a well-defined geometry and functionality. In this study, the integration of MOREs into scanning probe microscopy enabled the spectro-electrochemical detection of N, N, N, N'- Tetramethyl-p-phenyl-enediamine (TMPD) and its oxidized radical cation counterpart. UV-VIS spectroscopy capabilities of MOREs were optimized through tip-to-substrate distance variations. To demonstrate the applicability of MOREs to electrochemical single live cell imaging, oxygen production was detected in living algae (Eremosphaera viridis) by local illumination and concurrent electrochemical measurements.