Microalgae-derived carbon quantum dots enhance photosynthesis and accumulation of energy storage compounds in microalgal communities

With growing concerns over climate change, microalgae are considered promising feedstocks for third-generation biofuels due to their rapid growth and high CO₂ fixation capacity. Carbon quantum dots (CQDs) can modulate light wavelengths to improve microalgal solar utilization and biomass yield. Reducing CQDs synthesis costs and improving energy extraction efficiency could substantially decrease the microalgal biofuel production cost. In this study, CQDs were synthesized by a top-down hydrothermal method using mixed microalgal biomass as the carbon source. The nanostructure of the resulting microalgae-derived CQDs was confirmed by TEM and particle size analysis (3–16 nm). The effects on the original algal community were then evaluated under green, red, and full-spectrum light, and compared them with commercial blue, yellow, and red CQDs. The results indicate that under full-spectrum light, the microalgae-derived CQDs outperformed the commercial quantum dots in promoting microalgal growth and enhancing photosynthetic pigment content. Specifically, compared to the control group, the contents of chlorophyll a, chlorophyll b, and carotenoids increased by 43.5%, 360.7%, and 48.5%, respectively. Furthermore, despite inducing a degree of oxidative stress, the microalgae-derived CQDs did not cause significant growth inhibition. On the contrary, they boosted the synthesis of high-value metabolic products. Under full-spectrum light, the yields of lipids and proteins in the experimental group treated with microalgae-derived CQDs increased by 112.6% and 114.0%, respectively, relative to the control group. Overall, microalgae-derived CQDs exhibit dual functions of enhancing photosynthesis and metabolic productivity in microalgae, offering potential applications in bioenergy production and algal biotechnology. • Microalgae-derived CQDs were synthesized via a top-down hydrothermal method • Synthesized CQDs enhanced growth and metabolism despite inducing oxidative stress • Cluster analysis identified beneficial experimental conditions for microalgae • The underlying activated cellular pathways were subsequently investigated