Flotation Reagent Stress-Induced Extracellular Polymeric Substance Protein Secondary Structure in Shewanella oneidensis MR-1 Dictates the Morphology and Performance of Extracellular Polymeric Substance-Mediated ZnS Quantum Dots.

Extracellular polymeric substance (EPS)-mediated biosynthesis is a sustainable route for heavy metal valorization into quantum dots (QDs), yet how the EPS protein secondary structure regulates QD properties remains undefined. Herein, EPS from Shewanella oneidensis MR-1 cultivated under flotation reagent stress was utilized to synthesize high-performance ZnS QDs. Sodium butyl xanthate exhibited the optimal induction effect, significantly lowering the α-helix/(β-sheet + random coil) ratio in EPS. This structural shift promotes a more extended network, serving as a spatially ordered template for rapid, uniform ZnS nucleation. Analyzing QD materials mediated by distinct EPS layers (LB-EPS and TB-EPS) across treatments revealed strong correlations of this ratio with their size uniformity and specific surface area. Conversely, the QD yield and fluorescence intensity were governed primarily by chemical group abundance and synergistic structural-chemical factors, respectively. This dual regulatory mechanism demonstrates that manipulating the EPS protein structure is as crucial as modulating its chemical composition for nanomaterial biosynthesis.