Synthesis of sulfur-doped carbon quantum dots from Solanum nigrum for ciprofloxacin detection in yogurt samples and antibacterial activity

Abstract

In this study, S-CQDs were fabricated through a green and secure hydrothermal process, the carbon source was derived from the traditional Chinese medicinal herb Solanum nigrum and thiourea served as the sulfur precursor. The characterization results indicated that the S-CQDs presented a spherical shape, featuring a mean particle diameter of 3.96 nm and a lattice spacing measuring 0.19 nm. Surface functional groups such as amides, amino groups, and carboxyl groups were identified, contributing to their physicochemical properties. The S-CQDs demonstrated high selectivity and sensitivity toward CIP, spanning a linear detection range covering 0–0.4 μmol L⁻¹. Additionally, these materials displayed substantial antibacterial efficacy against both S. aureus and E. coli, with MIC values of 1.6 mg mL⁻¹ and 0.8 mg mL⁻¹ for each bacterium, respectively. Mechanistic investigations indicated that the positively charged S-CQDs electrostatically interacted with negatively charged bacterial membranes, disrupting membrane integrity and ultimately leading to bacterial cell death. This work establishes a novel approach for developing multifunctional S-CQDs, highlighting their promising applications in clinical diagnostics, environmental monitoring and antimicrobial therapies.