Sugarcane bagasse is an abundant biomass waste and a promising carbon source for preparing carbon-based materials such as carbon quantum dots (CQDs). Low quantum yield is a major problem for sugarcane bagasse-based carbon quantum dots. Heteroatom-doped modification is an efficient approach to improve the quantum yield. A facile hydrothermal carbonization method was applied to synthesize the nitrogen-doped carbon quantum dot N-CQDs using urea as the nitrogen source. The synthetic procedure was determined by the single-factor experiments and the response surface methodology (RSM) based on Box–Behnken design (BBD). The optical properties of optimized N-CQD-13 were more excellent than those of undoped CQD. Higher quantum yields (both absolute and relative) were observed in N-CQD-13. Additionally, N-CQD-13 exhibited high stability for long-time storage and excellent pH tolerance in aqueous solutions. N-CQD-13 were applied to detect Fe³⁺ in aqueous solutions with a low detection limit of 0.44 μM. The fluorescence lifetime decay of the N-CQD-13 solutions untreated and treated with Fe³⁺ indicated the probable involvement of a dynamic fluorescence-quenching mechanism. Thus, this work explored a reliable method for the high-quality utilization of bagasse.

Chlamydomonas reinhardtii polysaccharides (CRPs) are bioactive compounds derived from C. reinhardtii, yet their potential in cancer therapy remains largely unexplored. This study optimized the ultrasound-assisted extraction conditions using response surface methodology and proceeded with the isolation and purification of these polysaccharides. The optimal extraction conditions were identified as a sodium hydroxide concentration of 1.5%, ultrasonic power of 200 W, a solid-to-liquid ratio of 1:25 g/mL, an ultrasonic treatment time of 10 min, and a water bath duration of 2.5 h, yielding an actual extraction rate of 5.71 ± 0.001%, which closely aligns with the predicted value of 5.639%. Infrared analysis revealed that CRP-1 and CRP-2 are α-pyranose structures containing furoic acid, while CRP-3 and CRP-4 are β-pyranose structures containing furoic acid. Experimental results demonstrated that all four purified polysaccharides inhibited the proliferation of cervical (HeLa) hepatoma (HepG-2) and colon (HCT-116) cancer cells, with CRP-4 showing the most significant inhibitory effect on colon cancer and cervical cancer, achieving inhibition rates of 60.58 ± 0.88% and 40.44 ± 1.44%, respectively, and significantly reducing the migration of HeLa cells. DAPI staining confirmed that the four purified polysaccharides inhibit cell proliferation and migration by inducing apoptosis in HeLa cells. CRP-1 has the most significant inhibitory effect on the proliferation of liver cancer cells. This study not only elucidates the potential application of C. reinhardtii polysaccharides in cancer therapy but also provides a scientific basis for their further development and utilization.