Optically Transparent Thin-Film Electrode Chip for Spectroelectrochemical Sensing

A novel microfabricated optically transparent thin-film electrode chip for fluorescence and absorption spectroelectrochemistry has been developed. The working electrode was composed of indium tin oxide (ITO); the quasi-reference and auxiliary electrodes were composed of platinum. The stability of the platinum quasi-reference electrode was improved by coating it with a planar, solid state Ag/AgCl layer. The Ag/AgCl reference was characterized with scanning electron microscopy and energy-dispersive X-ray spectroscopy. Cyclic voltammetry measurements showed that the electrode chip was comparable to a standard electrochemical cell. Randles-Sevcik analysis of 10 mM K3[Fe­(CN)6] in 0.1 M KCl using the electrode chip gave a diffusion coefficient of 1.59 × 10–6 cm2/s, in comparison to the value of 2.38 × 10–6 cm2/s using a standard electrochemical cell. By using the electrode chip in an optically transparent thin-layer electrode (OTTLE), the absorption based spectroelectrochemical modulation of [Fe­(CN)6]3–/4– was demonstrated, as well as the fluorescence based modulation of [Ru­(bpy)3]2+/3+. For the fluorescence spectroelectrochemical determination of [Ru­(bpy)3]2+, a detection limit of 36 nM was observed.