Proteolysis-regulated excited state electron transfer of Ag₂S/In(OH)₃@BSA nanocomposites for fluorescence-photoelectrochemistry dual-mode biosensing of heparin

Sharing the same photoexcitation process, fluorescence (FL) and photoelectrochemistry (PEC) accomplish optical-optical and optical-electrochemical switches respectively, and are both widely used in diverse fields. However, since FL and PEC are mutually exclusive in principle, it is difficult to obtain intense FL and PEC responses in a system, limiting FL-PEC dual-mode applications. In this study, Ag₂S quantum dots (QDs) and In(OH)₃ nanoblocks (NBs) are simultaneously synthesized by BSA-templated bio-mineralization, and the excited state electrons of Ag₂S/In(OH)₃@BSA nanocomposites (NCs) are further regulated by a proteolysis process. Owing to the coating of BSA, excited state electrons primarily return to ground state via radiation transition, resulting in a robust FL signal. When BSA is hydrolyzed by trypsin, the excited state electrons preferentially transfer to the electron acceptors, and the exposed Ag₂S/In(OH)₃@BSA NCs generate a strong PEC signal. Consequently, heparin, acting as an inhibitor of trypsin, can regulate the FL-PEC switch, allowing for the quantification of heparin by both the decrease in FL signals and the increase in PEC signals. Therefore, a dual-mode biosensor is established to detect heparin using FL and PEC signals, with linear ranges of 0.75–750 U mL⁻¹ and 3.75 × 10⁻³ to 37.5 U mL⁻¹, and limits of detection of 0.68 U mL⁻¹ and 4.97 × 10⁻⁴ U mL⁻¹, respectively. Additionally, the biosensor is used to monitor the rapid metabolism of heparin within 20 h in rats. Overall, this work demonstrates that manipulating excited state electrons of nanomaterials through a biological process offers an alternative perspective for designing FL-PEC dual-mode sensing systems.