Engineering of Heterojunction-Mediated Biointerface for Photoelectrochemical Aptasensing: Case of Direct Z‑Scheme CdTe-Bi₂S₃ Heterojunction with Improved Visible-Light-Driven Photoelectrical Conversion Efficiency

This work presents a heterojunction-mediated photoelectrochemical (PEC) biointerface for selective detection of microcystin-LR (MC-LR) by introducing a direct Z-scheme heterojunction as efficient visible-light-driven photoactive species. Specifically, the Z-scheme type CdTe-Bi₂S₃ heterojunction was designed and synthesized as an ideal photoactive material, which exhibited higher PEC activity as compared with either CdTe quantum dots or Bi₂S₃ nanorods due to the improved photogenerated charges separation efficiency of heterojunction. Then the MC-LR aptamer was employed for selective recognition of MC-LR target, which was immobilized on the CdTe-Bi₂S₃ film by the formation of phosphor-amidate bonds between the phosphate group of aptamer and amino group of the chitosan film on the electrode. The proposed aptasensor showed a photocurrent signal due to the photoactive CdTe-Bi₂S₃ heterojunction, while the presence of MC-LR resulted in a dose-responsive decrease in PEC response, which allowed the quantification analysis of MC-LR by measuring the photocurrent signal of the fabricated aptasensor. Under optimal conditions, the resulted PEC aptasensor showed wide linear range (0.01–100 pM) and low detection limit (0.005 pM) for MC-LR determination with high selectivity and acceptable reproducibility. Finally, the proposed aptasensing method was successfully applied in MC-LR detection in real water samples.