An in situ engineered CuCo2S4@CuCo2O4 heterojunction with an O–S interpenetrated interface as a photoanode for selective photoelectrochemical bioanalysis†
In this work, an integrated electrode strategy is put forward to enhance photoexcited charge separation, in which a CuCo2S4@CuCo2O4 nanoneedle array heterojunction with an O–S interpenetrated interface is synthesized directly on a carbon cloth (CC) substrate via a hydrothermal process followed by a controlled in situ exterior sulfurization method. CuCo2S4@CuCo2O4 as a binder-free photoanode exhibits a high sensitive photocurrent response due to the unique design and construction of the integrated electrode. The vertically aligned CuCo2S4@CuCo2O4 nanoneedle architecture with wide open channels improves light scattering and harvesting, and maintains abundant active edge sites for spatially separating redox reactions. In particular, the superior co-presence of an O–S interpenetrated interface in both components of the electrode gradually formed in the sulfurization process act as a smooth bridge to promote photoexcited charge shuttling with a low barrier, and thoroughly promote electron/hole separation, further boosting the photoelectrocatalytic activity of the electrode. A novel photoelectrochemical (PEC) sensor with CuCo2S4@CuCo2O4/CC as a photoanode was constructed for the selective detection of L-Cysteine (L-Cys) without any biomolecule auxiliary. This PEC platform is effectively shielded from the interference of glutathione (GSH) and other coexisting amino acids due to the formation of a Cu–S bond, steric effects and its different redox properties. The applicability of this method was also investigated by the determination of L-Cys in human serum, urine and injection samples, with satisfactory results. This work provides a feasible strategy for the fabrication of an integrated electrode, and offers an insight into the exploitation of PEC for bioanalytical purposes.