Choline chloride-thiourea deep eutectic solvent (DES) was prepared and used to microwave-assisted synthesis of nitrogen, sulfur, and chloride doped carbon dots (N, S, Cl-CDs). In this innovative approach, DES is a solvent and a doping agent. The synthesized carbon dots (CDs) were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis), and fluorescence spectroscopy. The average size of N, S, Cl-CDs was 7 nm. The N, S, Cl-CDs had a quantum yield of 26.5% as the result of heteroatoms doping in CDs. The method was based on quenching of the fluorescence intensity by Fe3+ interaction with CDs and then N, S, Cl/CDs + Fe3+ system displayed a sensitive and selective turn-on fluorescence in the presence of naproxen. Linear range and detection limit for naproxen were 0.05–70 μM and 25 nM, respectively. Applicability of this nanoprobe was tested in naproxen determination in pharmaceutical tablets and the method was validated by high-performance liquid chromatography. The mechanism was also studied.
