An approach towards continuous production of silver nanoparticles using Bacillus thuringiensis

Abstract

Applying the principles of green chemistry for the synthesis of nanoparticles (NPs) is an emerging field in the current era. Continuous production of NPs, i.e. simultaneous bacterial growth and NP production, if possible, would be more effective for different NP mediated applications. Hence, our approach here is to optimize the method to produce and extract silver nanoparticles (AgNPs) during growth of the bacteria Bacillus thuringiensis. The fabricated AgNPs were obtained when the bacteria were grown at a minimum inhibitory concentration of AgNO₃ in culture medium. The microorganism produced elemental silver NPs with particular surface physico-chemical properties pertaining to the cellular moieties acting as a capping agent. Fabrication of the NPs was confirmed using UV-Vis absorbance spectra, attenuated total reflection Fourier transform infrared spectra, zeta analysis, and field emission scanning electron micrographs. The UV-Vis and IR studies together indicated the presence of proteins on the NP surface. The fabricated NPs were further purified using size exclusion chromatography (SEC), and the presence of the NPs in different elutions was further confirmed using UV-Vis, IR spectroscopes, and TEM. The yield, upon purification, was 98.75 μg of AgNPs from 500 mL of the culture, which is a relatively good yield. Additionally, the purified AgNPs were found to have a relatively stronger antibacterial activity against Escherichia coli than commercially available AgNPs. The work shows that a microorganism with resistance to significant concentrations of metal ions can be used for continuous production of metal NPs for industrial as well as biological applications.