N,S-doped carbon dots derived from tryptophan for sensitive and selective detection of meropenem in live cells, human urine, and water samples

Meropenem (MP) is an important carbapenem antibiotic used as a last-line treatment that requires precise quantification for therapeutic drug monitoring and environmental antibiotic surveillance. Herein, nitrogen, sulfur co-doped carbon dots (N,S-CDs) were derived from L-tryptophan and thiourea for MP detection. The prepared N,S-CDs were characterized by using UV–VIS, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and fluorescence spectroscopy. The interaction with MP led to systematic quenching of fluorescence (λ em = 457 nm, λ ex = 350 nm), a Stern–Volmer constant Ksv = 3.97 × 10 6 M −1 , a binding constant Ka = 9.07 × 10 6 M −1 , and a decrease in the fluorescence lifetime from 6.45 to 5.68 ns. A linear response was exhibited throughout the 0–390 nM range (R 2 = 0.990) with a limit of detection (LOD) of 6.8 nM. The sensor demonstrated high selectivity toward MP with a 1250-fold excess of coexisting inorganic ions, biomolecules, and structurally related carbapenem antibiotics. Intracellular fluorescence imaging and concentration-dependent intracellular MP detection were also demonstrated in live PC3 cells with negligible cytotoxicity (cell viability > 80% up to 10 mg/mL), indicating its potential for clinical therapeutic drug monitoring and environmental surveillance. The probe was successfully validated for the analysis of MP in pharmaceutical formulations, human serum, urine, and environmental water samples, with recoveries (%) in the range of 98%–102%. This work presents N,S-CDs as a robust, sensitive, and biocompatible analytical tool for clinical, pharmacological, and environmental MP surveillance.