Enhanced photoelectrochemical sensing of Pb2+ based on Cu/Mn:ZnInSe ternary quantum dots coupled with G-quadruplex DNAzyme

Novel Cu/Mn:ZnInSe ternary quantum dots (QDs) were synthesized from low-cost inorganic salts and natural biomolecules combined with titanium dioxide (TiO₂) for the first time using a one step in situ hydrothermal method to prepare a TiO₂/Cu/Mn:ZnInSe QD photoelectrochemical (PEC) sensing interface for lead ion detection. In contrast to the photoelectric conversion efficiency of the FTO/TiO₂ and FTO/TiO₂/ZnInSe electrodes, that of the FTO/TiO₂/Cu/Mn:ZnInSe electrode was evidently improved. The structure, morphology and conductivity of the FTO/TiO₂/Cu/Mn:ZnInSe electrode were confirmed using scanning electron microscopy (SEM) and the electrochemical method. Under the optimal conditions of electrode preparation, optimal experimental parameters (pH values of the detection medium and buffer solution) were obtained. Based on the high selectivity of nucleic acid aptamer sensors in detecting heavy metals, the G-quadruplex (G4) was modified on the FTO/TiO₂/Cu/Mn:ZnInSe electrode. Coupling the Pb²⁺-induced G4 DNAzyme structure with biocatalysis precipitation (BCP) enabled the detection limit of Pb²⁺ to be 10 nM. This work has opened up different perspectives for sensor design in PEC detection, providing a universal format for the future development of the PEC environment and biological analysis.