The influence of the initial molar ratio of water relative to tetraethyl orthosilicate (TEOS) precursor and the content of Nafion ionomer in sol-gel-derived silica composites on the voltammetric response of electrodes modified with these composites for [Re-I(DMPE)(3)](+) was investigated. The slow diffusion of [Re-I(DMPE)(3)](+) in Nafion can be significantly improved by dispersing Nafion in sol-gel-derived silica, and the diffusion of [Re-I(DMPE)(3)](+) in such a composite increases with the increase in water/TEOS molar ratio and the decrease in Nafion content. With the mass ratio of Nafion relative to sol-gel-derived silica being 40:100 and the initial molar ratio of water relative to TEOS being 20:1, the electrodes modified with the derived Nafion-silica nanocomposite exhibited an apparent peak current increase rate, during preconcentration of [Re-I(DMPE)(3)](+), that was approximately three times faster than the corresponding Nafion-modified electrode. Compared with bare indium-tin oxide (ITO) glass, the composite-coated ITO glass showed a 25-fold enhancement in voltammetric response to [Re-I(DMPE)(3)](+). The suitability of the developed optically transparent Nafion-silica composite for spectroelectrochemical sensing of[Re-I(DMPE)(3)](+) was demonstrated. The [Re-I(DMPE)(3)](+) extracted into the coating (similar to 0.4 mu m in thickness) was electrolyzed to [Re-II(DMPE)(3)](2+) Under attenuated total reflection mode, the in-situ electrogenerated chromophore [Re-II(DMPE)(3)](2+) was monitored by probing its interaction with the evanescent field of light of a selected wavelength. Thus, the elements required for a spectroelectrochemical sensor with three modes of selectivity were demonstrated: partitioning into the film on an electrode surface and an electrochemically modulated optical signal.