According toBeveridge (1997), the mechanisms which are considered for the biosynthesis of nanoparticles includes efflux systems, alteration of solubility and toxicity via reduction or oxidation, bioabsorption, bioaccumulation, extracellular complexation or precipitation of metals, and lack of specific metal transport systems 33. The cell wall of the microorganisms also plays a major role in the intracellular synthesis of nanoparticles. The cell wall being negatively charged interacts electrostatically with the positively charged metal ions. The enzymes present within the cell wall bioreduce the metal ions to nanoparticles, and finally the smaller sized nanoparticles get diffused of through the cell wall 34.
Shankar, S. S., Ahmad, A., and Sastry, M. (2003). “Geranium leaf assisted biosynthesis of silver nanoparticles,” Biotechnology Progress 19(6), 1627-1631.
Synthesis of Gold Nanoparticles by Plant System: One of the important approaches for biosynthesis of nanoparticles is employing the use of plant extract for biosynthesis reaction. In the case of Azadirachta indica leaf extract a competition bioreduction of Au3+ and Ag+ ions presented simultaneously in solution was observed. A bimetallic Au core-Ag shell nanoparticles synthesis occurred in solution 78. Aloe vera leaf extract has been used for gold nanotriangle and spherical silver nanoparticles synthesis 79. The kinetics of GNPs formation was monitored by UV-vis absorption spectroscopy and transmission electron microscopy (TEM).
Synthesis of Gold Nanoparticles by Fungal System: The fungi are one of the good biological agents in the synthesis of metal nanoparticles. Biosynthesis of metal nanoparticles using fungi such as F. oxysporum 51-53, Colletotrichum sp. 54, Trichothecium sp., Trichoderma asperellum, T. viride, 55-57, Phaenerochaete chryso sporium 58, Fusarium semitectum 59, Aspergillus fumigates 60, Coriolus versicolor 61, Phoma glomerata 62, Penicillium brevicompactum 63, Cladosporium cladosporioides 64, Penicillium fellutanum 65 and Volvariella volvacea 66has been extensively studied. Indeed, fungi are regarded as more advantageous for GNPs biosynthesis as compared to other microorganisms because;
One of the requirements for advancement of nanotechnology are the development of reliable experimental protocols for the synthesis of nanomaterials over a range of biological compositions, sizes and high monodispersity. An attractive possibility of green nanotechnology is to use micro-organisms in the synthesis of nanoparticles. Recently, the utilization of biological systems, especially fungi, has emerged as a novel method for the synthesis of nanoparticles. Nanoparticles are considered as fundamental molecular building blocks for nanotechnology. They are the starting points for preparing many nanostructured materials and devices. In this paper we report the extracellular biosynthesis of silver nanoparticles (AgNPs) by using a fungus named Trichoderma Reesei (also known as Hypocrea jecorina). In the biosynthesis of AgNPs by this fungus, the fungus mycelium is exposed to the silver nitrate solution. That prompts the fungus to produce enzymes and metabolites for its own survival. In this process the toxic Ag+ ions are reduced to the nonetoxic metallic AgNPs through the catalytic effect of the extracellular enzyme and metabolites of the fungus. Absorption UV-Visible light spectroscopy is used to follow up with the reaction process. Fluorescence emission spectroscopy is used to produce detailed information on the progress of reduction of silver nitrate (formation of silver nanoparticles) on the nanosecond timescale. Fourier transform infrared spectroscopy is used for quantitative analyses of the reaction products. Our measurements indicate that extracellular biosynthesis of AgNPs by Trichoderma reesei produces AgNPs with the diameters in the range of 5-50 nm. Trichoderma Reesei is an environmentally friendly fungus, and it is well known for its formation of extracellular enzyme and metabolites in very large amounts, much higher than other fungi. The present process is an excellent candidate for industrial scale production of silver nanoparticles.
Ghorbani, H. R. (2013). “Biosynthesis of silver nanoparticles using Salmonella typhirium,” Journal of Nanostructure in Chemistry 3(1), 1-4. DOI: 10.1186/2193-8865-3-29
The methods of biosynthesis can employ either microbial cells or plant extract for production of nanoparticles. Biosynthesis of nanoparticles is an exciting recent area to the large repertoire of various methods of nanoparticles synthesis and now, nanoparticles have entered a commercial exploration period. Gold nanoparticles (GNPs) are presently under intensive study for applications in optoelectronic devices, ultrasensitive chemical and biological sensors and as catalysts 3. Nanoparticles are metal particles and exhibit different shapes like spherical, triangular, rod, etc. Research on synthesis of nanoparticles is the current area of interest due to the unique visible properties (chemical, physical, optical, etc.) of nanoparticles compared with the bulk material 4-5.
The synthesis of gold nanoparticles has received considerable attention and has been a focus of research due to their high chemical and thermal stability, fascinating optical, electronic properties, and promising applications such as nanoelectronics, biomedicine, sensing, and catalysis. Different physical and chemical methods for gold nanoparticles synthesis are known but these methods are either expensive or are not eco-friendly due to use of hazardous chemicals, stringent protocol used during the process. These drawbacks necessitate the development of nonhazardous and greener methods for gold nanoparticles synthesis. Therefore, there has been tremendous excitement in the study of gold nanoparticles synthesis by using natural biological system. Microorganisms thus play a very important role in the eco-friendly and green synthesis of metal nanoparticles. The inherent, clean, nontoxic and environment friendly ability of eukaryotic and prokaryotic microorganisms, plants system to form the metal nanoparticles is particularly important in the development of nanobiotechnology. This review contains a brief outlook of the biosynthesis of gold nanoparticles using various biological resources, characterization and their potential application in various fields.
Njagi, E. C., Huang. H., Stafford, L., Genuino, H., Galindo, H. M., Collins, J. B., Hoag, G. E., and Suib, S. L. (2011). “Biosynthesis of iron and silver nanoparticles at room temperature using aqueous sorghum bran extracts,” Langmuir 27, 264-271.
Mechanism of Biosynthesis of Nanoparticles: Biosynthesis is the phenomena which takes place by means of biological processes or enzymatic reactions. These eco-friendly processes are referred as green and clean technology, and can be used for better synthesis of metal nanoparticles from microbial cells 31. Microorganisms can survive and grow in high concentration of metal ion due to their ability to fight against stress 32. The exact mechanism for the synthesis of nanoparticles using biological agents has not been devised yet as different biological agents react differently with metal ions and also there are different biomolecules responsible for the synthesis of nanoparticles. In addition, the mechanism for intra- and extracellular synthesis of nanoparticles is different in various biological agents 30.
As far as crop yields are concerned, wheat, maize, and rice are the most productive crop stalks in the world. Recent research concerning corn straw has been more comprehensive, mainly concentrated on bio-energy. Moreover, much research in this area is focused on the assessment of the supply chain or the exclusion of economic benefits (Batidzirai et al. 2016).Our previous work has included a preliminary study on the effect of the synthesis of AgNPs using wheat straw biomass (Ma et al. 2016). It was found that the AgNPs particles could be efficiently synthesized within 90 min, and its antibacterial effect was noticeable. The object of this study was to utilize rice straw to synthesize silver nanoparticles. The biosynthesis conditions were investigated, and the main properties of AgNPs were analyzed. The antibacterial activities of synthetic AgNPs on common gram-positive and gram-negative bacteria were studied. Also the antibacterial activity of AgNPs on antibiotics was explored.