Enhancing Water Stability and Cathode Photocurrent of CH ₃ NH ₃ PbI ₃ Perovskite via Bidentate Ligand-Bridged Covalent Passivation for PEC-EC Dual-Mode Assay of PTP1B Activity

Cathodic photoelectrochemical (PEC) sensing has attracted significant attention due to its remarkable anti-interference capability but is severely limited by the lack of high-performance photocathodic materials. Recently, CH₃NH₃PbI₃ (MAPbI₃) perovskite demonstrated a large cathodic photocurrent; however, its instability in aqueous solution meant that it was rarely used in PEC assays. Herein, mercaptopropionic acid (MPA) was employed to simultaneously anchor MA⁺ and [PbI₆]^4- units via a dual covalent bonding strategy. The developed MPA-MAPbI₃ showed remarkable stability in a Tris-HCl aqueous solution and enhanced the cathodic photocurrent. Thus, taking protein tyrosine phosphatase 1B (PTP1B) as a model, the application of MPA-MAPbI₃ in the PEC assay was explored. Methylene blue (MB) was sealed into the pores of mesoporous Fe₃O₄ beads (m-Fe₃O₄), and a phosphorylated peptide chain (P-peptide) was used as the gatekeeper based on the coordination interaction between the phosphate group of P-peptide and the Fe atom of m-Fe₃O₄. In the presence of PTP1B, the P-peptide underwent dephosphorylation, leading to the moving away of the P-peptide from m-Fe₃O₄. Thus, MB was released and captured by 6-mercapto-β-cyclodextrin which was immobilized on the MPA-MAPbI₃-modified electrode through host-guest interaction. Due to the electrochemical signal of MB and the quenching effect of MB on the PEC signal of MPA-MAPbI₃, the PTP1B activity assay was used with a wide linear response range and low detection limit based on PEC and EC modes. This work greatly promotes the application of MAPbI₃ perovskites in PEC sensing, and the developed PEC-EC dual-mode sensing platform has great potential in protein phosphatase-targeted drug discovery and early diagnosis of protein phosphatase-related diseases.