Enzymatic growth of single-layer MnO2 nanosheets in situ: Application to detect alkaline phosphatase and ascorbic acid in the presence of sulfanilic acid functionalized graphene quantum dots

Abstract In this work, a rapid fluorescence “turn off-on” assay was developed to detect alkaline phosphatase (ALP) and ascorbic acid (AA) based on sulfanilic acid functionalized graphene quantum dots (SGQDs) and MnO 2 nanosheets, which was fabricated through in situ formation of MnO 2 nanosheets in the presence of SGQDs. ALP catalyzed the hydrolysis of amifostine to WR1065 [S-2-(3-Aminopropylamino)ethanethiol)], which in the presence KMnO 4 yielded MnO 2 nanosheets and WR33278 [polyamine disulfide form of WR1065]. Then, the energy transfer platform was established by attaching SGQDs to MnO 2 nanosheets via WR33278 as the linker. As a result, the fluorescence of SGQDs quenched efficiently by MnO 2 nanosheets. AA could reduce MnO 2 into Mn 2+ and trigger the disintegration of the MnO 2 nanosheets. As a result, the SGQDs were released and the quenched fluorescence was recovered efficiently. Moreover, both the addition of ALP and AA can cause the change of solution color owing to the redox reaction of MnO 2 nanosheets. Thus, MnO 2 nanosheets could also be used as colorimetric probes for the detection of ALP and AA through directly visualizing the color variation by bare eyes.