Investigating soil and ATCC bacterial strains for their ability to synthesize anisotropic gold nanoparticles

The current study investigated 17 bacterial strains for their ability to synthesize gold nanoparticles (AuNPs) from the aryldiazonium gold(III) salt (DS-AuCl₄). The study aims to investigate the ability of bacterial cell biomass in the stationary phase of growth to synthesize AuNPs at 28 °C and 37 °C. Eleven bacterial strains were isolated from soil and identified using the VITEK® 2 system and 16S rRNA sequencing. An additional six strains were obtained from the American Type Culture Collection (ATCC). The investigated Gram-positive and Gram-negative bacterial strains successfully produced anisotropic AuNPs at a cell density of 2.0 McFarland (6.0 × 10⁸ CFU/mL). Nanoparticle formation was faster when samples were incubated at 37 °C than at 28 °C across all bacterial strains. The results of UV-vis spectroscopy confirmed the presence of AuNPs, with peaks observed centered at 550 nm. High-resolution transmission electron microscopy (HR-TEM) revealed a variety of morphologies, including spheres, rods, triangles, pentagons, hexagons, irregular shapes, and flower-like structures. Gram-positive and Gram-negative bacteria synthesized AuNPs of sizes 38.7 ± 26.0 and 34.0 ± 18.6 nm, respectively. Lattice-spacing analysis confirmed the formation of metallic AuNPs. Energy-dispersed X-ray spectroscopy (EDS) validated the presence of gold in the samples, and X-ray photoelectron spectroscopy (XPS) confirmed the elemental composition of AuNPs at 84.0 eV. These nanoparticles have potential applications in cancer therapy and diagnosis, antibacterial treatments, and drug delivery. KEY POINTS: • The AuNPs were synthesized using various bacterial strains • The gold precursor is aryldiazonium gold(III) salt • Various anisotropic morphologies were obtained.