Functionalized carbon quantum dots as fluorescent nanoprobe for determination of tetracyclines and cell imaging

Nitrogen and sulfur co-doped carbon dots (N, S-CQDs) with high fluorescent, water-soluble, low-toxicity properties were synthesized by microwave-assisted hydrothermal approach. The prepared N, S-CDs exhibited high selectivity in detection of tetracyclines (TCs) and displayed a fast-responsive fluorescence quenching signal in the mixture, which are mainly attributed to the inner filter effect (IFE). The synthesized N, S-CQDs are successfully used as a fluorescent nanoprobe for the determination of CTC in milk samples (with excitation/emission maxima at 373/424 nm). The limit of detection (LOD) is 71 ng mL^-1, and the recoveries of spiked samples range from 96 to 104% with a relative standard deviations (RSDs) less than 2.7% (n = 3). Additionally, the cytotoxicity and optical imaging performance of N, S-CQDs were preliminarily evaluated. The results indicate the low-toxicity and good biocompatibility of the N, S-CQDs and their promising future as fluorescent-imaging agents in pharmaceutical analysis. Graphical Abstract Synthesis flowchart and application of nitrogen and sulfur dual-doped carbon quantum dots.