When MnSiO3 meets ratiometric fluorescence: A facile, cost-effective ratiometric fluorescent platform based on oxidase-like MnSiO3 nanozyme for versatile Total Antioxidant Capacity (TAC) measurements

The level alterations of antioxidants are highly associated with various oxidative stress-related diseases, food quality and drug safety problems, which enables the reliable and accurate determination of total antioxidant capacity (TAC) become progressively significant. Herein, for the first time, we explored the catalytic effect of MnSiO 3 nanozyme with oxidase-like activity towards different fluorescent substrates, and introduced ratiometric fluorescence to MnSiO 3 -based biosensing. By harnessing MnSiO 3 -propelled catalytic oxidation of two fluorescent substrates with contrary responses (Scopoletin, SC and o-phenylenediamine, OPD), we constructed a facile, cost-effective ratiometric fluorescent (RF) platform for TAC measurement. In the absence of antioxidants, SC and OPD can be oxidized, and the synergistic effect of fluorescence resonance energy transfer (FRET) and inner-filter-effect (IFE) between SC and oxidized OPD (Ox-OPD) will result in the weak fluorescence of Ox-SC at 465 nm and the strong one of Ox-OPD at 562 nm, respectively. However, the addition of antioxidants will dissociate MnSiO 3 , generating the recovered high/low fluorescence values of both substrates. Through monitoring the FI 465 /FI 562 changes, the RF analysis of different antioxidants (Cys, AA, GSH) with satisfactory sensitivity is performed and the TAC measurements in diverse real samples (human serums, beverages, and drugs) are successfully accomplished. Moreover, the system demonstrates high selectivity and could compete with the commercial TAC test kits.