One-Step Synthesis of CuO–Cu2O Heterojunction by Flame Spray Pyrolysis for Cathodic Photoelectrochemical Sensing of l-Cysteine

CuO–Cu2O heterojunction was synthesized via a one-step flame spray pyrolysis (FSP) process and employed as photoactive material in construction of a photoelectrochemical (PEC) sensing device. The surface analysis showed that CuO–Cu2O nanocomposites in the size less than 10 nm were formed and uniformly distributed on the electrode surface. Under visible light irradiation, the CuO–Cu2O-coated electrode exhibited admirable cathodic photocurrent response, owing to the favorable property of the CuO–Cu2O heterojunction such as strong absorption in the visible region and effective separation of photogenerated electron–hole pairs. On the basis of the interaction of l-cysteine (l-Cys) with Cu-containing compounds via the formation of Cu–S bond, the CuO–Cu2O was proposed as a PEC sensor for l-Cys detection. A declined photocurrent response of CuO–Cu2O to addition of l-Cys was observed. Influence factors including CuO–Cu2O concentration, coating amount of CuO–Cu2O, and applied bias potential on the PEC response toward l-Cys were optimized. Under optimum conditions, the photocurrent of the proposed sensor was linearly declined with increasing the concentration of l-Cys from 0.2 to 10 μM, with a detection limit (3S/N) of 0.05 μM. Moreover, this PEC sensor displayed high selectivity, reproducibility, and stability. The potential applicability of the proposed PEC sensor was assessed in human urine samples.