A green approach for silver nanoparticles preparation by cell-free extract from Trichoderma reesei fungi and their characterization

• Published in: Materials research express Vol. 6; no. 9; pp. 95040 - 95051
• Main Authors: Gemishev, O T, Panayotova, M I, Mintcheva, N N, Djerahov, L P, Tyuliev, G T, Gicheva, G D
• Format: Journal Article
• Language: English
• Published: IOP Publishing 10.07.2019
• Subjects: silver nanoparticles biosynthesis; silver nanoparticles characterization
• ISSN: 2053-1591; 2053-1591
• DOI: 10.1088/2053-1591/ab2e6a

Silver nanoparticles (AgNPs) exhibit unique optical, photochemical, electronic, photoelectrochemical properties and they are non-toxic to the mammalian cells at low concentrations. The biosynthesis of AgNPs is a green alternative to chemical and physical methods. The use of fungi is more efficient compared to other bio-alternatives because of the possibility for easy cultivation on a large scale and simple biomass harvesting. Trichoderma reesei fungi produce extracellular enzymes that can reduce silver ions (Ag+) to AgNPs. The present study describes an extracellular biosynthesis of AgNPs from AgNO3 solution by using cell-free water extract (CFE) of T reesei PF biomass. The impact of the components of the medium where the T. reesei PF were cultivated, the amount of biomass used for obtaining the CFE, the initial concentration of AgNO3 solution and the time for Ag+ reduction to AgNPs have been studied. It has been found that for all studied cultivation media the amount of biotransformed Ag+ increases with time and with the initial concentration of AgNO3. The higher amount of extracted wet biomass (i.e. the higher concentration of extracted metabolites) leads to a higher biotransformation of Ag+ to Ago. Having in mind the quantitative data from the ICP analysis of isolated and washed AgNPs produced at various experimental conditions, it could be concluded that the optimum formation of AgNPs was achieved when T reesei fungi were cultivated in media containing 0.1% corn steep liquor, 10% biomass extracted to obtain CFE and 10 mM concentration of the AgNO3 precursor was used. The formation of AgNPs was proved by XPS and TEM analysis. The HRTEM micrographs confirmed Ag metallic nanoparticles in crystal phase. The TEM images showed initial formation of AgNPs clusters with size 1-4 nm that increase further up to 15-25 nm. The NPs were stabilized by capping effect of the biomolecules, as the FTIR spectroscopy revealed. The small size, the particles' narrow size distribution, nontoxicity, stability and the negative zeta potential which could facilitate attachment of biologically active substances render the produced AgNPs into suitable carriers of such substances.