Insights of green and biosynthesis of nanoparticles

Nanoparticles (NPs) are term used for particles whose sizes, at least at one dimension, are within 1–100 nm. NPs show various shapes and properties that are different from the bulk material of the same chemical composition, and can be designed and tailored by choosing suitable synthesis, production route, or method for NPs desired purposes and applications. Some NPs occur in nature, such as interplanetary and atmospheric dusts, then some viruses, and many can be synthesized using biological and/or biomimetic synthesis, which are considered greener methods than NP chemical or physical syntheses. Among the most explored NPs, metallic NPs (MNPs) stand out. MNPs can be spherical or nonspherical in form, with many types of shapes, such as nanocubes, nanoflowers, nanorods, nanostars, nanoreefs, nanoboxes, nanochains, nanowhiskers, and nanofibers. Gold, platinum, and silver nonspherical NPs show many fascinating properties that are explored for biomedical, nanotechnical, and environmental applications (trace metal detection). Herein, some insights of green biosynthesis of NPs are presented with emphasis on intracellular, extracellular and different bio-based methods. The most biosynthetic methods use reduction agents to promote metallic ions for the production of MNPs and tailor MNP shapes, while the use of stabilizing agents ensures that MNPs do not aggregate and control their sizes. Biological synthesisoften counts on mild conditions and all-in-one reduction/oxidation and stabilization, but some explore two or more steps for MNP production. Intracellular syntheses use fungi or bacteria for MNP reduction, while extracellular syntheses use reduction, biosorption, enzyme- or latex- mediated processes, and are less laborious because of no need to recover and purify MNPs. Bio-based methods mimic biological synthesis by using isolated compounds from plants, bacteria, and fungi. Other NPs can also be prepared by applying biosynthetic processes, such as metal-oxide particles, which gained attention because of interesting applications, such as magnetic NPs. All of the cited processes explore nonhazardous reagents and a great majority is environmentally friendly and clean. Although reproducible in small-scale, NPs’ large-scale production is still a challenge and there are no commercially available biogenic NPs. Therefore, current trends need to tackle challenges of green biosynthesis of NPs to their wide-scale fabrication.