Ultrasensitive colorimetric sensing strategy based on ascorbic acid triggered remarkable photoactive-nanoperoxidase...

Recently, exploitation of nanozymes for signal amplification has aroused extensive research interesting in the fields of analytical chemistry and nanoscience. Herein, we introduced a new sensing strategy based on the ascorbic acid (AA) precisely regulated Ag₃PO₄ nanozyme for signal amplification. AA can reduce the partial Ag⁺ on the surface of Ag₃PO₄ nano-particles to form Ag° particles and result in the formation of Ag°/Ag₃PO₄ heterostructure. Due to surface plasmon resonance (SPR), the Ag° particles in heterostructure can act as the co-catalysts to enhance the electron-hole separation and the interfacial charge transfer, leading to a highly efficient oxidase mimicking activity for catalyzing the oxidation of the substrate of 3,3,5,5-tetramethylbenzidine (TMB) under visible light. Impressively, the activity enhancement of Ag₃PO₄ nano-peroxidase was linearly depended on the AA concentrations. Based on this feature, we employed it for multiple biological detections. For example, L-ascorbic acid-2-O-α-D-glucopyranosyl (AAG) was designed for α-glucosidase substrate, which can be hydrolyzed by α-glucosidase and lead to AA release. Further, the signal of α-glucosidase activity can be efficiently enlarged by Ag₃PO₄ nanozyme. Taking advantages of the powerful signal amplification by Ag₃PO₄ nanozymes, we developed the multiple sensing assays for monitoring AA in rat brain microdialysates, detection of α-glucosidase activity and its inhibitors (anti-diabetic drugs). The assay allowed the ultrasensitive colorimetric detection of α-glucosidase inhibitor with an ultra-low detection limit of 10 nM, and a naked-eye detection of the inhibitor concentration as low as 1 μM. The sensing strategy based on AA precisely regulated Ag₃PO₄ nano-peroxidase provides a promising candidate platform for highly stable and efficient cascaded signal amplification in biosensing field.