Polyvinylpyrrolidone-stabilized Pt nanoclusters as robust oxidase mimics for selective detection of ascorbic acid

In this work, the Pt nanoclusters with an average size of 1.7 ± 0.3 nm were prepared by a facile and green method using polyvinylpyrrolidone (PVP) as both stabilizer and reductant. The oxidase-like activity of PVP-stabilized Pt nanoclusters (PVP-Pt NCs) was investigated by the catalytic oxidation of o-phenylenediamine (OPD). The mechanism studies indicated that PVP-Pt NCs performed as oxidase enzyme mimics by catalyzing the dissolved oxygen to generate the reactive oxygen species (singlet oxygen and superoxide anion) intermediates. Ascorbic acid (AA) could also be oxidized to dehydroascorbic acid (DHA) which could react with OPD to generate a fluorescent compound. On the basis of the robust oxidase-like activity of PVP-Pt NCs, both colorimetric assay and fluorescence method for AA determination were established. Compared with colorimetric assay, the fluorescence method showed higher sensitivity and selectivity for AA detection. The proposed fluorescence method with the LOD of 1.17 μM could overcome the interference of most reducing substances and showed promising applications in biosensor. The as-prepared PVP-Pt NCs possessed intrinsic oxidase-like property by catalyzing dissolved oxygen to ROS (superoxide anions (·O 2 - ) and singlet oxygen ( 1 O 2 )) which could oxide the OPD to OPD ox . The inhibition of AA to the catalytic oxidation of OPD was employed to establish the colorimetric assay for AA determination. AA could also be oxidized to DHA by·O 2 - and 1 O 2 intermediates, and the DHA could react with OPD to form QD with a fluorescence emission peak at 434 nm. The fluorescence method for AA detection was carried out when the solution changed to yellow color which was the signal of the reaction terminal. Comparing with colorimetric assay, the fluorescence method exhibited enhanced sensitivity and selectivity.