Bacteria and nanosilver: the quest for optimal production

Abstract

Silver nanoparticles (AgNPs) have potential uses in many applications, but current chemical production methods are challenged by scalability, limited particle stability, and the use of hazardous chemicals. The biological processes present in bacteria to mitigate metallic contaminants in their environment present a potential solution to these challenges. Before commercial exploitation of this technology can be achieved, the quality of bacteriogenic AgNPs needs to be improved for certain applications. While the colloidal and morphological stabilities of biogenic AgNPs are widely regarded as superior to chemogenic particles, little control over the synthesis of particle morphologies has been achieved in biological systems. This article reviews a range of biosynthetic reaction conditions and how they affect AgNP formation in bacteria to understand which are most influential. While there remains uncertainty, some general trends are emerging: higher Ag + concentrations result in higher AgNP production, up to a point at which the toxic effects begin to dominate; the optimal temperature appears to be heavily species-dependent and linked to the optimal growth temperature of the organism. However, hotter conditions generally favour higher production rates, while colder environments typically give greater shape diversity. Little attention has been paid to other potentially important growth conditions including halide concentrations, oxygen exposure, and irradiation with light. To fully exploit biosynthetic production routes as alternatives to chemical methods, hurdles remain with controlling particle morphologies and require further work to elucidate and harness. By better understanding the factors influencing AgNP production a foundation can be laid from which shape-controlled production can be achieved.

Green Chemistry: Evolution in Architecting Schemes for Perfecting the Synthesis Methodology of the Functionalized Nanomaterials

“…However, the increase in the production rate also results in the formation of non-spherical NMs and large aggregates have been found to be synthesized if highly favorable conditions for the production rate are applied. [86] In the case of cell-free extract, the production rate increases with the increase in the temperature, increase in incubation time, increase in electromagnetic/ionizing radiation, decrease in mixing intensity, and increase in aerobic conditions. The parameters of pH and increase in the concentration of nitrate ions (precursor salt) do not influence the production rate of the Ag NMs.…”

“…should also be taken in account during synthesis. [86] The presence of these additional factors makes the optimization of the microorganism based produc- Extracellular production of the Ag NMs was found to be stable for more than a year without precipitation [63] Saccharomyces cerevisiae…”

“…The parameters of pH and increase in the concentration of nitrate ions (precursor salt) do not influence the production rate of the Ag NMs. [86,87]…”

Biogenic Nanoparticles: Synthesis, Characterisation and Applications

“…These are some of the issues associated with biological synthesis; however, careful selection of microorganisms, optimization of control factors such as pH and temperature and concentration of precursors may allow the implementation of such methods in largescale production. It is also hypothesised that microbes can be genetically engineered to synthesise nanoparticles with greater control over shape and size [18,19].…”

<p>Functionalized Gold and Silver Bimetallic Nanoparticles Using <em>Deinococcus radiodurans</em> Protein Extract Mediate Degradation of Toxic Dye Malachite Green</p>

“…Biomaterials, such as nucleotides, 1 amino acids, 2 polypeptides and proteins, [3][4][5] cell extracts, [6][7][8][9][10] could be used as raw materials for reducing metal ions and producing metal nanoparticles (NPs). Metal NPs have demonstrated catalytic, mechanical, magnetic, thermal, optical, photoelectrochemical and biological properties.…”