A MnO nanosheet-based ratiometric fluorescent nanosensor with single excitation for rapid and specific detection of ascorbic acid.

Ascorbic acid (AA) detection in biological sample and food sample is critical for human health. Herein, a MnO nanosheet (MnO-NS)-based ratiometric fluorescent nanosensor has been developed for high sensitive and specific detection of AA. The MnO-NS presents peroxidase-like activity and can oxidize non-fluorescent substrate of o-phenylenediamine (OPDA) into fluorescent substrate, presenting maximum fluorescence at 568 nm (F). If MnO-NS is premixed with AA, the MnO-NS is then decomposed as Mn by AA, decreasing the fluorescent intensity of F. Meantime, AA is oxidized as dehydroascorbic acid (DHAA), which can react with OPDA to generate fluorescent substrate. A new fluorescence response is found at 425 nm (F). The dual fluorescent responses can be excited with a universal excitation wavelength, simplifying the detection procedure. With F/F as readout, limit of detection for AA reaches as low as 10.0 nM. Satisfactory recoveries are found for AA detection in serum and diverse beverages. The ratiometric strategy significantly eliminates false-negative and false-positive results, providing a cost-effective, rapid, and reliable way for AA detection in real sample.