Nature-derived carbon dots for ratiometric analysis: Bismuth-doped fluorescent probe for oyster shell determination in tablet dosage forms

• Innovative synthesis of WB-derived dual-emission fluorescent carbon dots. • Dual doping with bismuth oxide and folic acid enhances fluorescence properties. • Microwave-assisted process yields eco-friendly, fluorescent WB-n-CQDs. • WB-n-CQDs probe enables sensitive, selective OSC quantification in tablets. • Ratiometric analysis offers linearity and high accuracy for OSC determination. Wheat bran (WB), a major byproduct of the milling industry, is the most prevalent among various cereal bran residues. The substantial accumulation of WB biomass is driving the research community to seek innovative and economically viable applications for this bioresource. In this context, the potential for utilizing WB byproducts as nature-derived carbon quantum dots (n-CQDs) precursor has been highlighted. This research introduces an innovative, environmentally friendly, and effective WB-based n-CQDs (WB-n-CQDs) synthesized by microwave-assisted method. The developed WB-n-CQDs-based fluorescence probe, in combination with silver nitrate, demonstrates high sensitivity and selectivity for oyster shell calcium (OSC) quantification. The incorporation of bismuth oxide and folic acid as dopants effectively enhances the intensity of two emission peaks at 354 nm and 445 nm, thereby improving fluorescence ratiometric capabilities for measuring OSC. A variety of experimental techniques has been employed to investigate the structural, morphological, and optical characteristics of WB-n-CQDs, including Fourier-transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, fluorescence spectroscopy, UV–Vis spectroscopy, and high-resolution transmission electron microscopy. The experimental results demonstrated remarkable physical and chemical characteristics, highlighting the potential of WB-n-CQDs for their applications in green analytical chemistry. The fluorescence intensity of Ag-WB-n-CQDs demonstrated an acceptable linear correlation with OSC concentration levels ranging from 0.1 to 1.0 μg/mL, along with high recovery percentages that lie between 98 % and 102 %. The successful application of Ag-WB-n-CQDs for measuring OSC in its dosage forms demonstrates the promising potential of biomass-derived n-CQDs in sustainable and advanced sensing technologies.