Ecofriendly dual-emission cerium, nitrogen, and sulfur co-doped carbon dots as a ratiometric probe for spironolactone: An antioxidant-based approach

• Dual-emission cerium, nitrogen, and sulfur doped carbon dots (Ce-NSCDs) were synthesized. • The first microwave-assisted synthesis of Ce-NSCDs, in 60 seconds, is presented. • A Ce-NSCDs ratiometric probe for spironolactone determination is reported. • Spironolactone was determined based on an antioxidant approach. • TEM and XPS were employed to investigate the underlying mechanism. • Superior eco-friendliness was proved using greenness metric tools. Ratiometric probes are analytical tools that utilize a single probe with two or more emission signals to measure analyte concentrations, effectively correcting for measurement variations. Although several methods have been previously employed for spironolactone (SPR) determination, these methods often require expensive instrumentation, lengthy extraction or derivatization steps, and generate considerable chemical waste. In this study, a facile, rapid, and environmentally friendly ratiometric spectrofluorometric method for determining SPR is presented. Dual emission carbon dots co-doped with cerium, nitrogen, and sulfur (Ce-NSCDs) were formed through one-pot microwave-assisted pyrolysis, utilizing citric acid, urea, and ammonium cerium (IV) sulfate as precursors in just 60 seconds, for the first time. The Ce-NSCDs displayed dual emissions at 350 nm and 430 nm when excited at 320 nm. Notably, SPR enhanced the emission of Ce-NSCDs at 350 nm, while the emission at 430 nm remained unaffected. Transmission electron microscopy images indicated that SPR interacted with the surface of Ce-NSCDs, forming a shell. X-ray photoelectron spectroscopy investigations suggested a Ce(IV)/Ce(III) redox mechanism, where the intrinsic antioxidant activity of SPR enabled the modulation of the Ce(IV)/Ce(III) equilibrium, leading to enhanced emission. Consequently, a ratiometric sensing probe was developed based on the F 350 /F 430 emission ratio. The determination of SPR demonstrated excellent linearity (R 2 = 0.996) over a concentration range of 40 - 200 μg/mL, with a limit of detection of 13.08 μg/mL and exhibited good accuracy and precision (% recovery of 100 ± 2), and selectivity with excellent reproducibility (%RSD < 2%), confirming its precision and reliability. This innovative sensing strategy was successfully applied for the determination of SPR in pharmaceutical formulations, yielding satisfactory recovery results that demonstrate the method’s practical applicability and was shown to be environmentally benign.