Facile synthesis of sulfur and oxygen co-doped graphitic carbon nitride quantum dots for on-off detection of Cu 2+ in real samples and living cells

A fluorescent sulfur and oxygen co-doped graphitic carbon nitride quantum dots (S,O-CNQDs) were prepared from ethylenediaminetetraacetic acid disodium salt dihydrate and thiourea as the carbon and sulfur sources. The morphology and surface functional groups of S,O-CNQDs were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The fluorescence of S,O-CNQDs could be quenched efficiently by Cu²⁺under the optimum conditions. The S,O-CNQDs could function as an excellent fluorescent probe for Cu²⁺detection with a wide linear range of 0.50-15μM and a low detection limit of 0.58 nM. In addition, this fluorescent probe was employed for monitoring Cu²⁺in samples of tap water, lake water, human serum and urine with good recoveries from 99.0% to 110.0%. Moreover, the S,O-CNQDs with high cell penetration and low cytotoxicity were utilized for Cu²⁺detection in living cells. Owing to the excellent properties of S,O-CNQDs, the as-prepared S,O-CNQDs can be a potential candidate for biological applications.