Characterization of a Ruthenium(II) Complex in Singlet Oxygen-Mediated Photoelectrochemical Sensing

A water-soluble ruthenium(II) complex (L), capable of producing singlet oxygen (O-1(2)) when irradiated with visible light, was used to modify the surface of an indium-tin oxide (ITO) electrode decorated with a nanostructured layer of TiO2 (TiO2/ ITO). Singlet oxygen triggers the appearance of a cathodic photocurrent when the electrode is illuminated and biased at a proper reduction potential value. The L/TiO2/ITO electrode was first characterized with cyclic voltammetry, impedance spectroscopy, NMR, and Raman spectroscopy. The rate constant of singlet oxygen production was evaluated by spectrophotometric measurements. Taking advantage of the oxidative process initiated by O-1(2), the analysis of phenolic compounds was accomplished. Particularly, the O-1(2)-driven oxidation of hydroquinone (HQ) produced quinone moieties, which could be reduced back at the electrode surface, biased at -0.3 V vs Ag/AgCl. Such a light-actuated redox cycle produced a photocurrent dependent on the concentration of HQ in solution, exhibiting a limit of detection (LOD) of 0.3 mu mol dm(-3). The L/TiO2/ITO platform was also evaluated for the analysis of p-aminophenol, a commonly used reagent in affinity sensing based on alkaline phosphatase.

Automated summary

A water-soluble ruthenium(II) complex (L) was used to modify the surface of an indium-tin oxide (ITO) electrode decorated with a nanostructured layer of TiO2 (TiO2/ITO). Singlet oxygen (O-1(2)) produced by the complex under visible light irradiation triggers a cathodic photocurrent when the electrode is illuminated and biased at a proper reduction potential. The L/TiO2/ITO electrode was characterized and demonstrated efficient oxidation of phenolic compounds, with a limit of detection (LOD) of 0.3 mu mol dm(-3).