Chiral Gold Staining Enables In Situ Plasmonic Engineering for Single-Bacterium Microscopic Imaging Analysis

The geometric chirality of nanoscale materials originates from the asymmetric structures of the enantiomeric molecules. Herein, we introduce a universal strategy for fabricating in situ-synthesized Au nanostructures (issAu) on biological substrates using a simple staining solution of Au precursors, surfactant, and reductant. As a proof-of-concept, we integrated this staining reaction into bacterial systems, achieving the oriented growth of issAu on organism skeletons. With the involvement of exogenous cysteine enantiomers in the staining solution, enantiomeric molecules contribute to anisotropic growth of branched issAu and the evolution of plasmonic chirality. Through reaction optimization, we successfully engineer chiral issAu onto bacteria, constructing these nanobioheterostructures as versatile, bacterium-derived nanomaterials. The simple and rapid staining method based on chiral issAu growth solutions facilitates the in situ plasmonic engineering of pathogenic bacteria, enabling optical microscopy imaging of individual microbes. Our protocol provides an approach for the chiral nanoengineering of biological entities and exhibits high potential in antimicrobial and bioanalytical applications.