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Silver nanoparticles have extensive application in the development of new technologies in the areas of electronics, medicine and material sciences due to good conductivity and chemical stability. For example they find wide application as spectrally selective coatings for solar energy absorption, intercalation material for electrical batteries, optical receptors, catalysts in chemical reactions, bio labeling, photonics, optoelectronics, surface-enhanced Raman scattering (SERS) detection material and as antimicrobials.
The development of green processes for the synthesis of nanoparticles is evolving into an important branch of nanotechnology, because biological methods are considered safe and ecologically sound for the nanomaterial fabrication as an alternative to conventional physical and chemical methods. The green synthesis techniques are generally synthetic routes that utilize relatively non-toxic chemicals to synthesize nanomaterials, and include the use of non-toxic solvents such as water, biological extracts, biological systems and microwave assisted synthesis. Silver nano-particles
Many reports are available on the biogenesis of silver nanoparticles using several plant extracts, particularly neem leaf broth (Azadirachta indica), pelargonium graveolens (P.graveolens- geranium), geranium leaves (P. graveolens), medicago sativa (Alfalfa), aloe vera, emblica officinalis (amla, Indian Gooseberry) and few microorganisms. Similarly different plant constituents such as geraniol possess reducing property and reduce Ag+ to silver nanoparticles with a uniform size and shape in the range of 1 to 10 nm with an average size of 6 nm.
Factors for biosynthesis
Indian researchers have employed a single-step environmental friendly approach to synthesize silver nanoparticles. According to their report the biomolecules found in plants induce the reduction of Ag+ ions from silver nitrate to silver nanoparticles (AgNPs). The process of reduction is extra cellular and fast leading to the development of easy biosynthesis of silver nanoparticles. Plants during glycolysis produce a large amount of H+ ions along with NAD which acts as a strong redoxing agent which is responsible for the formation of AgNPs. Water-soluble antioxidative agents like ascorbic acids are further responsible for the reduction of AgNPs. These AgNPs produced show good antimicrobial activity against common pathogens.
The polyol components and the water-soluble heterocyclic components are largely accountable for the reduction of Ag ions and the stabilization of the nanoparticles, respectively. There are also reports on reductases and polysaccharides as factors involved in biosynthesis and stabilization of the nanoparticles, respectively.
Also the sunflower leaf extract was found to be promising in the development of silver nanoparticles.
Recently, efficient antibacterial activity was observed against multi drug resistant and highly pathogenic bacteria, including multi drug resistant Staphylococcus aureus, Salmonella typhi, Staphylococcus epidermidis and Escherichia coli by silver nanoparticles produced by the fungus F. acuminatum.
However, the synthesis of silver nanoparticles using such plant constituents or microorganisms has not yet been studied for a large number of natural compounds.