Fluorometric atrazine assay based on the use of nitrogen-doped graphene quantum dots and on inhibition of the activity of tyrosinase.

A fluorometric assay is described for the determination of the herbicide atrazine. The assay is based on the use of tyrosinase and fluorescent nitrogen-doped graphene quantum dots (N-GQDs). The N-GQDs were synthesized via one-pot hydrothermal reaction starting from citric acid and ammonia. Their fluorescence excitation and emission maxima are at 355 and 435 nm, and the quantum yield is 18%. Tyrosinase catalyzes the oxidation of dopamine to form dopaquinone which reduces the fluorescence of the N-GQDs through a dynamic quenching process. On addition of atrazine, the catalytic activity of tyrosinase is inhibited. This leads to less formation of dopaquinone and less reduction of fluorescence. The assay has a linear response in the 2.5-100 ng·mL atrazine concentration range, and the detection limit is 1.2 ng·mL. The assay was applied to the determination of atrazine in spiked environmental water samples. Graphical abstract Schematic presentation of the fluorometric assay of atrazine detection based on tyrosinase-induced fluorescence (FL) quenching effect on the nitrogen-doped graphene quantum dots (N-GQDs) and inhibitory effect of atrazine on tyrosinase.