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-C₃N₄) modified with a molecularly imprinted polymer (MIP). It was synthesized via reverse microemulsion. The resulting MIP@g-C₃N₄ 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-C₃N₄ probe. The effect was used to quantify quercetin in grape juice, tea juice, black tea, and red wine by fluorometry (λ_exc = 350 nm, λ_em = 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%. .