A water-soluble ruthenium(II) complex (L), capable of
producing
singlet oxygen (1O2) 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 1O2, the
analysis of phenolic compounds was accomplished. Particularly, the 1O2-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 μmol
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.