Resting-cell biocatalysis as a platform for cadmium sulfide quantum dot biosynthesis

Biogenic quantum dots (QDs) have attracted interest as an alternative route for producing semiconductor nanomaterials. However, their potential advantages over chemical synthesis depend on the production system and require case-specific evaluation. However, current microbial platforms often suffer from limited control over chemical nanoparticle synthesis, low stability, and challenging downstream processing. In this study, we developed and characterized a resting-cell strategy for the biosynthesis of cadmium sulfide (CdS) QD using the environmental bacterium Pseudomonas putida KT2440 and explored, for the first time, the potential of Cupriavidus necator H16 as a microbial chassis for QD production. Optimization of production conditions in P. putida KT2440 were stablished. Structural and elemental characterization confirmed the formation of CdS nanomaterials, while spectroscopic and DLS analyses demonstrated a time-dependent increase in nanoparticle size from 2.6 ± 0.5 nm to 6.6 ± 0.7 nm. Purified QD retained fluorescence for up to 3 months when stored in Tris–HCl buffer, highlighting the importance of storage conditions for preserving nanoparticle integrity. Under resting-cell conditions C. necator H16 generated fluorescent nanoparticles with emission properties that differed from those observed in P. putida . Comparative analyses further demonstrated that resting cells outperformed actively growing cultures, enabling faster QD formation and prolonged fluorescence stability. Collectively, these findings establish resting-cell biocatalysis as an efficient platform for sustainable QD production and expand the repertoire of microorganisms available for the biological synthesis of semiconductor nanomaterials.