Ratiometric fluorescence sensing of glutathione by using the oxidase-mimicking activity of MnO2 nanosheet.

In this work, a facile ratiometric fluorescence sensor for GSH measurement was designed based on MnO 2 nanosheet (NS), carbon dots (CDs), as well as a simple substrate o-phenylenediamine (OPD). Herein, MnO 2 NS played triple essential roles in the sensing system. First, it could be reduced by GSH through a special reaction, and therefore served as GSH recognizer. Second, it played as a fluorescence nanoquencher to strongly quench the fluorescence of CDs. Third, it could directly oxidize OPD to yield a luminescent product 2, 3-diaminophenazine (DAP) via the intrinsic oxidase-like activity. It revealed that MnO 2 NS could be reduced to Mn2+ in the presence of GSH. Thus its oxidase-like activity and fluorescence quenching abilities were inhibited, which then restricted the generation of DAP and recovered the fluorescence of CDs. Based on this phenomenon, a novel ratiometric fluorescence sensor for GSH determination was fabricated by measuring the ratio of fluorescent intensity of DAP to that of CDs. Besides, the constructed ratiometric fluorescent sensor, which could be facilely operated with single-wavelength excitation, exhibited high sensitivity and selectivity with a wider linear range and a lower detection limit. Image 1 • A facile single-wavelength excitation ratiometric fluorescence sensor was constructed for GSH. • MnO 2 nanosheets can not only effectively quench the fluorescence of CDs but also oxidize OPD into luminescent DAP due to its intrinsic oxidase-like activity. • DAP could also quench the fluorescence of CDs through the inner filter effect. [ABSTRACT FROM AUTHOR]