Combined SECM-fluorescence microscopy using a water-soluble electrofluorochromic dye as the redox mediator

A combined experiment of fluorescence and electrochemical microscopies was performed to highlight the possibility of using a unique water-soluble molecule as the redox mediator and fluorescence reporter. Resorufin was selected as it owns a highly luminescent redox state which can be easily converted into a non-emissive one by reduction at moderately negative potentials. In the feedback mode of Scanning Electrochemical Microscopy (SECM), it is shown that the fluorescence modulation amplitude is sensitive to the nature of the substrate as well as to the tip-substrate distance and can thus be utilized to record optical approach curves. Changing the polarization of the ITO substrate enables to move from positive to negative feedback and the fluorescence modulation amplitude is also sensitive to this change. Substrate generation-tip collection mode was also investigated showing that fluorescence intensity can be used to detect at the tip the species produced at the substrate with a higher accuracy than the electrochemical current.