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 theherbicide 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 435nm, 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 2.5-100ngmL(-1) atrazine concentration range, and the detection limit is 1.2ngmL(-1). The assay was applied to the determination of atrazine in spiked environmental water samples.