High sensitive ratiometric fluorescence analysis of trypsin and dithiothreitol based on WS2 QDs.

In this paper, a simple tungsten disulfide quantum dots (WS2 QDs)-based ratiometric fluorescence method was established for the detection of trypsin and 1, 4-dithiothreitol. Trypsin can hydrolyze cytochrome c into heme-peptide fragments with peroxidase-like activity. In the presence of hydrogen peroxide, the fragments can generates hydroxyl radicals, which can oxidize o-phenylenediamine (OPD) to form 2,3-diaminophenazine (DAP) with a fluorescence peak at 568 nm. DAP can quench the fluorescence of WS2 QDs at 448 nm via fluorescence resonance energy transfer (FRET). When 1, 4-dithiothreitol was present, it can react with hydroxyl radicals, and less OPD was oxidized, which accompanied by the fluorescence intensity of WS2 QDs increased and the fluorescence intensity of DAP decreased. Therefore, the fluorescence intensity ratio (F568/F448) can be used to monitor trypsin and 1, 4-dithiothreitol. A good linear calibration between fluorescence intensity ratio F568/F448 versus trypsin activity and1, 4-dithiothreitol concentration were obtained within 0.2-140 μg mL-1 and 20-200 μmol L-1, respectively. And the detection limit was 0.09 μg mL-1 for trypsin and 6.8 μmol L-1 for 1, 4-dithiothreitol, respectively. Furthermore, the developed ratiometric fluorescence method was successfully applied for trypsin and 1, 4-dithiothreitol assay in human serum samples.