A global approach of the mechanism involved in the biosynthesis of gold colloids using micro-algae

International audienceThe use of micro-algae for the production of noble metal nanoparticles has drawn much attention recently. This paper aims to address some questions raised by our earlier publications and some recent reports from other groups, among which the biological pathways involved in the bioreduction of noble metal cations into nanoparticles and the design of stable colloids. TEM micrographs, taken at the early stage of contact between cells and salt solutions, show undoubtedly that the biomineralization process occurs within the thylakoidal membranes, which are the organelles responsible for photosynthesis. We strongly believe that the available enzymes and their cofactors (enzymatic machinery) are the key molecules that allow such reduction, promoting therefore the formation of nanoparticles. In addition, by comparing the characteristics of gold colloids made by polysaccharides-producing and non-producing micro-algae strains, we demonstrate that the stability of those colloids is ensured predominantly by those biopolymers. These macrobiomolecules control partly the size and the shape of NPs

Improvement of kinetics, yield, and colloidal stability of biogenic gold nanoparticles using living cells of Euglena gracilis microalga

International audienceRecent years have witnessed a boom in the biosynthesis of a large variety of nanomaterials using different biological resources among which algae-based entities have been gaining much more attention within the community of material scientists worldwide. In our previously published findings, we explored some factors that governed the biofabrication of gold nanoparticles using living cultures of microalgae, such as the utilized microalgal genera, the phylum they belong to, and the impact of tetrachloroauric acid concentrations on the ability of these strains to perform the biosynthesis of gold nanoparticles once in contact with these cations. As a follow-up, we present in this paper an improvement of the features of bioproduced gold colloids using living cells of Euglena gracilis microalga when this species is grown under either mixotrophic or autotrophic conditions, i.e., exposed to light and grown in an organic carbon-enriched culture medium versus under autotrophic conditions. As an outcome to this alteration, the growth rate of this photosynthetic microorganism is multiplied 7–8 times when grown under mixotrophic conditions compared to autotrophic ones. Therefore, the yield, the kinetics, and the colloidal stability of the biosynthesized gold nanoparticles are dramatically enhanced. Moreover, the shape and the size of the as-produced nano-objects via this biological method are affected. In addition to round-shaped gold nanoparticles, particular shapes, such as triangles and hexagons, appear. These findings add up to the amassed knowledge toward the design of photobioreactors for the scalable and sustainable production of interesting nanomaterials