Fluorescence spectroscopy of gum arabic-derived carbon quantum dots: a green nanosensor for dantrolene determination via the inner filter effect.

Carbon quantum dots (CQDs) are promising fluorescent nanomaterials for analytical applications, but their structure-property relationships remain under-investigated, especially in biomass-derived systems. Herein, we report the ultrafast, one-pot, microwave-assisted synthesis (700 W, 4 min) of highly fluorescent CQDs from gum arabic, a renewable, low-cost, and GRAS-certified polysaccharide. Structural characterization by FTIR spectroscopy and transmission electron microscopy revealed a uniform spherical morphology (3.8 nm) with abundant oxygen-containing functional groups, providing excellent water solubility and high fluorescence quantum yield (35.5%). Spectroscopic studies of the photophysical properties revealed excitation-dependent fluorescence with an optimum λex/λem of 346/425 nm, attributed to surface defect states arising from the functionalized carbon core. Using these structure-derived photophysical properties, a fluorescence nanosensor was developed for the selective determination of dantrolene (DNT), a poorly metabolized muscle relaxant that persists in municipal wastewater. Mechanistic studies showed that fluorescence quenching occurs via the inner filter effect (IFE). The developed method shows excellent analytical performance (linear range of 3.0-60.0 µM and LOD of 0.6 µM) and was successfully applied for the determination of DNT in commercial capsules (recovery of 98.19-102.62%) and tap water samples (recovery of 94.19-96.94%), indicating its selectivity against common excipients, co-administered drugs, and inorganic ions. This work highlights the valorization of underutilized natural gums into high-performance sensing materials, provides clear structure-property-activity correlations in biomass-derived CQDs, and demonstrates their utility as a sustainable spectroscopic probe for environmental and pharmaceutical analysis.