Fluorometric determination of quercetin by using graphitic carbon nitride nanoparticles modified with a molecularly imprinted polymer.

The authors describe a fluorescent probe for sensitive and selective determination of quercetin, an indicator for the freshness of drinks. The probe consists of silica ball encapsulated graphitic carbon nitride (g-C3 N4 ) modified with a molecularly imprinted polymer (MIP). It was synthesized via reverse microemulsion. The resulting MIP@g-C3 N4 nanocomposite was characterized by fluorescence spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray powder diffraction. Quercetin quenches the fluorescence of the MIP@g-C3 N4 probe. The effect was used to quantify quercetin in grape juice, tea juice, black tea, and red wine by fluorometry (λexc  = 350 nm, λem  = 460 nm). Response is linear in the 10-1000 ng mL-1 quercetin concentration range. The detection limit is 2.5 ng mL-1 , recoveries range between 90.7 and 94.1%, and relative standard deviations are between 2.1 and 5.5%. Graphical abstract Schematic of the synthesis of the MIP@g-C3 N4 by a reverse microemulsion method. The probe was applied for the selective recognition and fluorometric determination of quercetin.