A snapshot of the electrochemical reaction layer by using 3 dimensionally resolved fluorescence mapping

Fluorescence confocal laser scanning microscopy under electrochemical control allows imaging of various reaction layers revealing heterogeneous versus homogeneous reactions.

The coupling between electrochemistry and fluorescence confocal laser scanning microscopy (FCLSM) allows deciphering the electrochemical and/or redox reactivity of electroactive fluorophores. This is demonstrated with phenoxazine electrofluorogenic species frequently used in bioassays by mapping the variation of fluorescence intensity with respect to the distance from the electrode. The electrochemical conversion of resorufin dye (RF) to non-fluorescent dihydroresorufin (DH) leads to a sharp decrease of the fluorescence signal in the vicinity of the electrode. In contrast, the direct reduction of resazurin (RZ) to DH leads to an unexpected maximum fluorescence intensity localized further away from the surface. This observation indicates that the initial electron transfer (heterogeneous) is followed by a chemical comproportionation step (homogeneous), leading to the formation of RF within the diffusion layer with a characteristic concentration profile. Therefore, in situ FCLSM affords a direct way to monitor such chemical reactivity in space and to decipher a new redox pathway that cannot be resolved solely by electrochemical means.

Reaction Layer Imaging Using Fluorescence Electrochemical Microscopy

The chemical confinement of a pH sensitive fluorophore to a thin-reaction layer adjacent to an electrode surface is explored as a potentially innovative route to improving the spatial resolution of fluorescence electrochemical microscopy. A thin layer opto-electrochemical cell is designed, facilitating the visualization of a carbon fiber (diameter 7.0 μm) electrochemical interface. Proton consumption is driven at the interface by the reduction of benzoquinone to hydroquinone and the resulting interfacial pH change is revealed using the fluorophore 8-hydoxypyrene-1,3,6-trisulfonic acid. It is demonstrated that the proton depletion zone may be constrained and controlled by the addition of a finite acid concentration to the system. Simulation of the resulting fluorescence intensity profiles is achieved on the basis of a finite difference model, with excellent agreement between the theoretical and experimental results.

Controlled functionalisation of single-walled carbon nanotube network electrodes for the enhanced voltammetric detection of dopamine

Acid functionalised SWNT network electrodes enhance the voltammetric detection of dopamine and minimise surface fouling.