Excellent performance of Ag6Si2O7 oxidase mimic endowed by self-released ions for rapid colorimetric determination with reduced operational interference

Abstract

Increasing attention has been directed towards oxidase mimics due to their catalytic ability toward enzyme substrates in the absence of H2O2, offering great colorimetric sensing potential in assays and diagnostics. However, slow electron-transfer and unstable absorbance over time often lead to unsatisfactory enzymatic reaction rates and unreliable readouts, significantly reducing detection efficiency and accuracy. Herein, we report on an Ag6Si2O7 nanozyme utilizing 3,3′,5,5′-tetramethylbenzidine (TMB) as a chromogenic substrate, demonstrating excellent oxidase-like activity and long-term stable colorimetric signals. Experimental results reveal that the excellent catalytic kinetics of Ag6Si2O7 (Km = 0.197 mM, Vmax = 5.1 × 10−7 M/s) are attributed to ultrafast electron transfer between Ag+ and TMB, mediated by Ag2O intermediates formed from self-released alkaline ions. Additionally, self-released H2SiO42− improves the stability of the oxidized substrate, resulting in a long-term stable colorimetric signal (∼20 min), which exhibits reliable accuracy regardless of the time point at which analyte is added within 20 min, thus eliminating the interference of individual operation time errors. Ascorbic acid (AA) is selected as the target molecule to assess the performance of the Ag6Si2O7-TMB colorimetric sensing system. This approach demonstrates a wide detection range from 5 to 300 μM and a detection limit of 0.452 μM. The developed colorimetric sensing strategy exhibits good stability, specificity, rapidity, and potential application in real sample detection.