Green synthesis of carbon quantum dots from soluble soybean polysaccharide for multifunctional applications

Carbon quantum dots (CQDs) were synthesized via a one-step hydrothermal route using soluble soybean polysaccharide (SSPS) as a green and renewable precursor. The resulting SSPS-derived CQDs (SCQDs) were uniform nanodots with average diameters ranging from 2.66 ± 0.69 nm to 2.81 ± 0.57 nm, exhibiting strong blue fluorescence and excellent water dispersibility. Structural characterization by TEM, XRD, FTIR, and XPS confirmed the amorphous carbon structure and the presence of abundant hydroxyl, carboxyl, and carbonyl groups on SCQDs, which contribute to their distinctive optical and functional properties. The SCQDs exhibited excitation-dependent photoluminescence with a quantum yield of 12.0 %. They also demonstrated potent radical scavenging activities of 91.3 % for ABTS and 79.4 % for DPPH, along with notable antibacterial properties. Furthermore, the SCQDs showed good biocompatibility within the concentration range of 50-500 μg/mL, maintaining cell viability above 70 % after 7 days of exposure. The SCQDs were successfully utilized for cellular imaging, Fe³⁺ and Pb²⁺ ion sensing, and preservation of strawberries and bananas. These results demonstrate the suitability of SSPS for serving as an effective precursor in the sustainable synthesis of multifunctional CQDs with significant potential for applications in biomedical imaging, environmental sensing, and active food packaging.