Fluorometric turn-on detection of ascorbic acid based on controlled release of polyallylamine-capped gold...

A fluorometric turn-on assay is described for ascorbic acid (AA). It is based on the controlled release of polyallylamine-stabilized gold nanoclusters (polyallylamine-AuNCs) from MnO₂ nanosheets. In an aqueous solution of near-neutral pH value, the positively charged capped AuNCs are adsorbed on the surface of the negatively charged MnO₂ nanosheets. The adsorption leads to the quenching of the fluorescence of the AuNCs. However, in the presence of AA, MnO₂ is reduced to Mn²⁺. This causes the destruction of the MnO₂ nanosheets. As a result, the fluorescence of the polyallylamine-AuNCs at 615 nm is recovered. This method for determination of AA is inexpensive, sensitive, and selective. It works in the 0.01 to 200 μM concentration range and has a 3.2 nM detection limit (for S/N = 3). Graphical abstract Gold nanoclusters (AuNCs) and polyallylamine can form polyallylamine-AuNCs to enhance the orange fluorescence of AuNCs. MnO₂ nanosheets can absorb polyallylamine-AuNCs, and this results in fluorescence quenching of polyallylamine-AuNCs. Ascorbic acid (AA) can reduce MnO₂ nanosheets, in this results in the fluorescence recovery of polyallylamine-AuNCs.