Abstract
The biosynthesis of Ag and Au nanoparticles (NPs) was investigated using an extremophilic yeast strain isolated from acid mine drainage in Portugal. Three distinct studies were performed, namely, the growth of yeast strain in presence of metal ions, the use of yeast biomass for the metal nanoparticles synthesis, and of the supernatant obtained after 24-hour incubation of yeast biomass in water. The extremophilic strain under study was able to grow up to an Ag ion concentration of 1.5 mM whereas an increase of Au ion concentration over 0.09 mM caused a strong inhibitory effect. A successful route for the metal NPs synthesis was obtained using the yeast biomass. When the washed yeast cells were in contact with Ag or Au solutions, AgNPs smaller than 20 nm were produced, as for the AuNPs diameter ranged from 30 to 100 nm, as determined through transmission electron microscopy and confirmed by energy-dispersive X-ray spectra. The supernatant-based strategy provided evidence that proteins were released to the medium by the yeasts, which could be responsible for the formation and stabilisation of the Ag NPs, although the involvement of the cell wall seems fundamental for AuNPs synthesis.
Highlights
Nowadays, research in nanotechnology deals with the development of eco-friendly processes for the synthesis of stable nanoparticles, possessing well-defined shapes, and controlled narrow sizes [1]
We explore for the first time the potential of a yeast strain, isolated from acid mine drainage in Portugal (Sao Domingos, Alentejo), to reduce silver and gold ions
The area under each curve (AUC) was calculated by integration of the optical density with time in a 6-day period, since AUC is described as sensitive to the differential effects of the lag phase, the rate of growth and the maximum absorbance obtained during the incubation time [13]
Summary
Research in nanotechnology deals with the development of eco-friendly processes for the synthesis of stable nanoparticles, possessing well-defined shapes, and controlled narrow sizes [1]. Microbial recovery of precious metals with the formation of their nanoparticles is a green alternative to the conventional methods, and it fulfils both issues aforementioned [2, 3]. Many biological systems such as bacteria [2, 4, 5], fungi [6], yeast [7, 8], and plants have been used for the biosynthesis of gold and silver nanoparticles, with welldefined size and distinct topography. According to Gericke and Pinches [11], the yeast Pichia jadinii (formerly Candida utilis), a fungal isolate from a metal-rich dump (isolate 6–3), and the fungus Verticillium luteoalbum present the ability to produce gold nanoparticles. The influence of Ag and Au ions on the yeast growth is addressed, as well as the role of the reducing sugar glucose on the formation of nanoparticles during yeast growth
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