Synthesis, characteristics, and applications of sustainable carbon quantum dots derived from biomass of recombinant...

Biomass-derived carbon quantum dots (CQDs) emerge as promising alternatives to traditional metal-based quantum dots across various fields. However, it is still a significant challenge to achieve precise surface functionalization with high quantum yield (QY). This study developed a strategy for synthesizing functionalized CQDs using the biomass of recombinant Zymomonas mobilis, which produces intracellular poly-3-hydroxybutyrate (PHB). A series of CQDs were synthesized and characterized at nano/micro-scale levels. The PHB-CQDs and S-PHB-CQDs derived from biomass of PHB-producing recombinant strains, particularly the sulfur-doped S-PHB-CQDs, demonstrated excellent optoelectronic properties, which achieved a high QY of 40.1%. The hydrothermal reaction facilitated the decomposition of bacterial cells and intracellular PHB, resulting in precise surface modification of CQDs with oxygen/nitrogen-containing groups. Notably, PHB-CQDs had a 14-fold enhancement in sensitivity for Fe³⁺ detection compared to those derived from wild-type strains without intracellular polymer. Furthermore, both PHB-CQDs and S-PHB-CQDs from Z. mobilis exhibited excellent recovery rates in environmental water samples, which were subsequently integrated into colorimetric paper chips for on-site Fe³⁺ monitoring successfully. This work thus establishes a sustainable approach for synthesizing functionalized CQDs with excellent optoelectronic properties from microbial biomass of recombinant microorganisms producing intracellular polymer rich in O/N functional groups, enabling precise surface engineering of CQDs for applications such as environmental monitoring.