Synthesis of copper–nitrogen codoped carbon quantum dots using frangipani as a carbon source and application of metronidazole determination

High-fluorescence Cu/N-codoped carbon quantum dots (Cu/NCQDs) were prepared by a one-step hydrothermal method using frangipani and copper acetate hydrate. The prepared Cu/NCQDs exhibited a nearly spherical morphology, and the average particle size was 2.58 nm. The surface of the Cu/NCQDs contains abundant hydrophilic groups –OH, –NH2 and –COOH, which explains their high water solubility. The Cu/NCQDs exhibited high-intensity, stable blue fluorescence that is independent of the excitation wavelength. As metronidazole can effectively quench the fluorescence intensity of Cu/NCQDs, a metronidazole fluorescence-detection method using Cu/NCQDs as the fluorescence probe was developed, and the quenching mechanism was studied. The method has the advantages of simplicity, speed, and low cost. Besides, the linear equation was F = − 3.235 + 9.064 C(MNZ)(μmol/L), the correlation coefficient (R2) was 0.996, and the detection limit was 0.28 μmol/L. Further, the metronidazole content in actual samples was determined using this method; the recovery rates of the metronidazole tablets and honey samples were 96.8–103.7%, and relative standard deviation was lower than 6%.