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 K 3 [Fe(CN) 6 ] in 0.1 M KCl using the electrode chip gave a diffusion coefficient of 1.59 × 10 –6 cm 2 /s, in comparison to the value of 2.38 × 10 –6 cm 2 /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.