Determination of folic acid via its quenching effect on the fluorescence of MoS2 quantum dots.

Molybdenum disulfide quantum dots (MoS2 QDs) are used in a fluorometric method for the determination of folic acid (FA) based on fluorescence quenching. The MoS2 QDs synthesized by a hydrothermal method possess bright blue fluorescence (with excitation/emission maxima of 325/415 nm), quantum yield of 3.7%, and excellent storage stability in solution (30 days in the refrigerator). Their fluorescence is quenched by FA, and intensity decreases linearly in the 0.1 to 125 μM FA concentration range. The detection limit is 0.1 μM (at S/N = 3), and the relative standard deviation (for n = 5) is 2.8% for 25 μM concentrations of FA. Studies on the quenching mechanism suggest that the effect is due to static quenching. The FA in commercial FA tablets was successfully determined. Graphical abstract Schematic representation of the hydrothermal method for the preparation of molybdenum disulfide quantum dots (MoS2 QDs) with about 2.7 ± 0.5 nm diameter using Na2MoO4 and L-cysteine as Mo and S sources, and the fluorescence method for the determination of folic acid (FA) based on fluorescence quenching of MoS2 QDs.