http://users.encs.concordia.ca/~mojtaba/elec6271/silver%20nanoparticles.pdf

Silver nanoparticles: green synthesis and their antimicrobial activities.

Here, we present a review of the antibacterial effects of silver nanomaterials, including proposed antibacterial mechanisms and possible toxicity to higher organisms. For purpose of this review, silver nanomaterials include silver nanoparticles, stabilized silver salts, silver–dendrimer, polymer and metal oxide composites, and silver-impregnated zeolite and activated carbon materials. While there is some evidence that silver nanoparticles can directly damage bacteria cell membranes, silver nanomaterials appear to exert bacteriocidal activity predominantly through release of silver ions followed (individually or in combination) by increased membrane permeability, loss of the proton motive force, inducing de-energization of the cells and efflux of phosphate, leakage of cellular content, and disruption DNA replication. Eukaryotic cells could be similarly impacted by most of these mechanisms and, indeed, a small but growing body of literature supports this concern. Most antimicrobial studies are performed in simple aquatic media or cell culture media without proper characterization of silver nanomaterial stability (aggregation, dissolution, and re-precipitation). Silver nanoparticle stability is governed by particle size, shape, and capping agents as well as solution pH, ionic strength, specific ions and ligands, and organic macromolecules—all of which influence silver nanoparticle stability and bioavailability. Although none of the studies reviewed definitively proved any immediate impacts to human health or the environment by a silver nanomaterial containing product, the entirety of the science reviewed suggests some caution and further research are warranted given the already widespread and rapidly growing use of silver nanomaterials.

https://link.springer.com/content/pdf/10.1007%2Fs11051-010-9900-y.pdf

A review of the antibacterial effects of silver nanomaterials and potential implications for human health and the environment

Silver nanoparticles are nanoparticles of silver which are in the range of 1 and 100 nm in size. Silver nanoparticles have unique properties which help in molecular diagnostics, in therapies, as well as in devices that are used in several medical procedures. The major methods used for silver nanoparticle synthesis are the physical and chemical methods. The problem with the chemical and physical methods is that the synthesis is expensive and can also have toxic substances absorbed onto them. To overcome this, the biological method provides a feasible alternative. The major biological systems involved in this are bacteria, fungi, and plant extracts. The major applications of silver nanoparticles in the medical field include diagnostic applications and therapeutic applications. In most of the therapeutic applications, it is the antimicrobial property that is being majorly explored, though the anti-inflammatory property has its fair share of applications. Though silver nanoparticles are rampantly used in many medical procedures and devices as well as in various biological fields, they have their drawbacks due to nanotoxicity. This review provides a comprehensive view on the mechanism of action, production, applications in the medical field, and the health and environmental concerns that are allegedly caused due to these nanoparticles. The focus is on effective and efficient synthesis of silver nanoparticles while exploring their various prospective applications besides trying to understand the current scenario in the debates on the toxicity concerns these nanoparticles pose.

/pdf/silver-nanoparticles-mechanism-of-antimicrobial-action-3x1asgjbb2.pdf

Silver nanoparticles: mechanism of antimicrobial action, synthesis, medical applications, and toxicity effects

Biological synthesis of metallic nanoparticles.

Nanosilver: a nanoproduct in medical application.

Biological synthesis of silver nanoparticles using the fungus Aspergillus flavus

A novel one-pot ‘green’ synthesis of stable silver nanoparticles using soluble starch

Biomimetics of silver nanoparticles by white rot fungus, Phaenerochaete chrysosporium

We have reported a novel in situ synthesis protocol for silver nanoparticles onto cotton fabrics. Here, cotton fabric immersed in silver nitrate solution is autoclaved at 15 psi, 121 degrees C for 15 min. At this temperature and pressure, the aldehyde terminal of starch (residual size material on cotton fabric) reduced the silver nitrate to silver metal and simultaneously stabilized the nanoparticles on fabric itself. The UV-visible absorption spectrum of both cotton fabrics and bath solution showed a typical absorption peak at 420 nm corresponding to the surface plasmon resonance of silver nanoparticles. With the help of transmission electron micrographs, the average size of the dislodged silver nanoparticles in water is calculated to be 20.9 +/- 13.7 nm. This silver nanoparticles impregnated cotton fabrics showed excellent antibacterial activity against Staphylococcus aureus and bacteriostasis activity against Klebsiella pneumoniae. Also, silver nanoparticles impregnated fabrics expressed significant UV-protection capability in comparison with the untreated fabrics.

Functional finishing of cotton fabrics using silver nanoparticles.

A simple route for the synthesis of silver-protein (core-shell) nanoparticles using spent mushroom substrate (SMS) has been demonstrated in this work. SMS exhibits an organic surface that reduces silver ions and stabilizes the silver nanoparticles by a secreted protein. The silver nitrate solution incubated with SMS changed to a yellow color from 24 h onward, indicating the formation of silver nanoparticles. The purified solution yielded the maximum absorbance at 436 nm due to surface plasmon resonance of the silver nanoparticles. X-ray analysis of the freeze-dried powder of silver nanoparticles confirmed the formation of metallic silver. Transmission electron microscopic analysis of the samples showed a uniform distribution of nanoparticles, having an average size of 30.5 +/- 4.0 nm, and its corresponding electron diffraction pattern confirmed the face-centered cubic (fcc) crystalline structure of metallic silver. The characteristic fluorescence of the protein shell at 435 nm was observed for the silver nanoparticles in solution, when excited at 280 nm, while Fourier transform infrared (FTIR) spectroscopy confirmed the presence of a protein shell. The silver nanoparticles were found to be stable in solution for more than 6 months. It is observed that the reducing agents from the safflower stalks caused the reduction of silver ions while protein secreted by the fungus stabilized the silver nanoparticles. These silver nanoparticles showed excellent antibacterial activity against two representative bacteria, Staphylococcus aureus (Gram positive) and Klebsiella pneumoniae (Gram negative), in spite of the presence of an organic layer as a shell. Apart from ecofriendliness and easy availability, "SMS" as a biomanufacturing unit will give us an added advantage in ease of handling when compared to other classes of microorganisms.

R.P. Nachane

Papers

Biological synthesis of silver nanoparticles using the fungus Aspergillus flavus

A novel one-pot ‘green’ synthesis of stable silver nanoparticles using soluble starch

Biomimetics of silver nanoparticles by white rot fungus, Phaenerochaete chrysosporium

Functional finishing of cotton fabrics using silver nanoparticles.

Silver-protein (core-shell) nanoparticle production using spent mushroom substrate.