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

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 MnO2 nanosheets, which was fabricated through in situ formation of MnO2 nanosheets in the presence of SGQDs. ALP catalyzed the hydrolysis of amifostine to WR1065 [S-2-(3-Aminopropylamino)ethanethiol)], which in the presence KMnO4 yielded MnO2 nanosheets and WR33278 [polyamine disulfide form of WR1065]. Then, the energy transfer platform was established by attaching SGQDs to MnO2 nanosheets via WR33278 as the linker. As a result, the fluorescence of SGQDs quenched efficiently by MnO2 nanosheets. AA could reduce MnO2 into Mn2+ and trigger the disintegration of the MnO2 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 MnO2 nanosheets. Thus, MnO2 nanosheets could also be used as colorimetric probes for the detection of ALP and AA through directly visualizing the color variation by bare eyes.