Microwave-assisted synthesis of watercress-derived N,S-doped carbon dots for sensitive spectrofluorimetric determination of rifaximin antibiotic: Greenness, blueness, and whiteness assessment

• The current study introduces a novel and ultrafast microwave-assisted synthesis of N,S-CDs using watercress as a green carbon source. • This work explains the use of N,S-CDs as fluorescent nanosensors to determine RFX. • Determination of RFX relies on the quantitative and selective quenching of the native fluorescence of N,S-CDs. • The developed method was successfully employed for the determination of the RFX in its tablets with high % recoveries. • The method demonstrated excellent green and blue characteristics based on the analytical Eco-scale, AGREE, MoGAPI, and BAGI metric tools. A rapid microwave-assisted method was developed for synthesizing watercress-derived nitrogen and sulfur carbon dots (N,S-CDs) in just one minute using thiourea as a nitrogen and sulfur source and watercress as a green carbon source. Different spectroscopic and microscopic techniques were used to characterize the N,S-CDs. The synthesized N,S-CDs exhibited maximum fluorescence emission at 386 nm after being excited at 320 nm. Rifaximin (RFX) could quench the native fluorescence of the N,S-CDs quantitatively based on the inner filter effect (IFE) and static quenching mechanisms. The results revealed a good linearity over the range of 0.2-30.0 µg/mL, with a correlation coefficient of 0.9996. The developed method demonstrated excellent accuracy, with recovery values between 99.16% and 99.97%, and good precision, as the %RSD values were ≤ 1.3% for both intra-day and inter-day precision. The detection and quantitation limits were found to be 0.06 µg/mL and 0.19 µg/mL, respectively. The method was successfully applied for determining RFX in its tablets with high selectivity. The developed method produced comparable results to those obtained by the published HPLC method in terms of precision and accuracy. Finally, the developed method demonstrated excellent green, blue, and white characteristics based on the results obtained via the analytical Eco-scale, AGREE, MoGAPI, BAGI, and RGB12 tools. The suggested method offers a sensitive, fast, and eco-friendly spectrofluorimetric methodology for estimating the RFX without requiring hazardous organic solvents or complicated equipment.