Ratiometric paramagnetic probe based on ABTS•+ and Mn2+ for detection of glutathione and revelation of the mechanism for MnO2 nanosheet induced oxidation of ABTS

Abstract

We designed a ratiometric paramagnetic probe based on electron spin resonance (ESR) signals of ABTS radical (ABTS•+) and Mn2+. Two ESR signals from different paramagnetic species (ABTS•+ and Mn2+) coexisting in the same solution were measured at the same time and were present in one spectrum. MnO2 nanosheets with oxidase-like properties were synthesized. The probe was used to investigate the oxidation mechanism of ABTS by MnO2 nanosheets. On one hand, MnO2 nanosheets catalyzed the generation of O2•− which oxidized ABTS to ABTS•+, and on the other hand, a small amount of ABTS was directly oxidized to ABTS•+ by MnO2 which was reduced to Mn2+. Glutathione (GSH) underwent a redox reaction with MnO2 nanosheets to yield Mn2+ with stable ESR signal. The concentration of MnO2 decreased in the presence of GSH, which inhibited the production of O2•− and ABTS•+. As a result, as the concentration of GSH increased, ESR signal of ABTS•+ descended and on the contrary ESR signal of Mn2+ ascended. Accordingly, the signal ratio of ABTS•+ to Mn2+ decreased with the increase of GSH concentration. The proposed ratiometric ESR probe could reduce the influence from background signal and improve the accuracy and sensitivity of the detection. We applied this strategy to the determination of GSH in human erythrocyte cells, and the results showed recoveries between 90.9 % and 92.6 %. With this method, simultaneously monitoring both nanozyme and its chromogenic substrate could be realized and thus a better understand of the mechanism for the function of MnO2 nanomaterial could be achieved.