Abstract
Nanocrystallites have garnered substantial interest due to their varying applications including catalysis. Consequently important aspects related to control of shape/size and syntheses through economical and non-hazardous means are desirable. Highly efficient bioreduction based natural fabrication approaches that utilize microbes and or -plant extracts are poised to meet these needs. Here we show that the gamma- proteobacterium, Shewanella oneidensis MR-1, can reduce tetrachloro aurate (III) ions, producing discrete extracellular spherical gold nanocrystallites. The particles were homogeneous with multiple size distributions and produced under ambient conditions at high yield, 88% of theoretical maximum. Further characterization revealed that the particles consist of spheres in the size range of 2-50 nm, with an average of 12±5 nm. The nanoparticles were hydrophilic, biocompatible, and resisted aggregation even after several months. The particles are likely capped by a detachable protein/peptide coat. UV-vis and Fourier transform infrared spectroscopy, X-ray diffraction, energy dispersive X-ray spectra and transmission electron microscopy measurements confirmed the formation as well the crystalline nature of the nanoparticles. The antibacterial activity of these gold nanoparticles was assessed using Gram-negative (E. coli and S. oneidensis) and Gram-positive (B. subtilis) bacteria. Toxicity assessments divulged that the particles were neither toxic nor inhibitory to any of these bacteria.
