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

Green synthesis of metal nanoparticles using plants

Synthesis of metallic nanoparticles using plant extracts.

Five plant leaf extracts (Pine, Persimmon, Ginkgo, Magnolia and Platanus) were used and compared for their extracellular synthesis of metallic silver nanoparticles. Stable silver nanoparticles were formed by treating aqueous solution of AgNO(3) with the plant leaf extracts as reducing agent of Ag(+) to Ag(0). UV-visible spectroscopy was used to monitor the quantitative formation of silver nanoparticles. Magnolia leaf broth was the best reducing agent in terms of synthesis rate and conversion to silver nanoparticles. Only 11 min was required for more than 90% conversion at the reaction temperature of 95 degrees C using Magnolia leaf broth. The synthesized silver nanoparticles were characterized with inductively coupled plasma spectrometry (ICP), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and particle analyzer. The average particle size ranged from 15 to 500 nm. The particle size could be controlled by changing the reaction temperature, leaf broth concentration and AgNO(3) concentration. This environmentally friendly method of biological silver nanoparticles production provides rates of synthesis faster or comparable to those of chemical methods and can potentially be used in various human contacting areas such as cosmetics, foods and medical applications.

Rapid biological synthesis of silver nanoparticles using plant leaf extracts

https://www.rsc.org/suppdata/gc/b6/b615357g/b615357g.pdf

Green synthesis of silver nanoparticles using Capsicum annuum L. extract

In this paper we describe the size-controlled synthesis ofa silver nanocomplex based on the reduction of silvernitrate (AgNO3) by UV-irradiated tungstosilicate acid [H4(SiW12O40), TSA] solution. This method allows the synthesis of ellipsoidal particles with an average size that is tunable between 2.4 and 84 nm by varying the molar ratio of silver nitrate to TSA, the pH of the reaction solution, and the reaction temperature. Silver nanorods can be formed from the ellipsoidal nanoparticles by controlling the aging time. The formation mechanism of these nanorods is also discussed. The nanoparticles are characterized by UV/Vis spectroscopy, FTIR spectroscopy, XRD analysis, XPS, electron diffraction (ED), TEM, and with a Zetasizer instrument. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Size- and Shape-Controlled Synthesis and Assembly of a Silver Nanocomplex in UV-Irradiated TSA Solution

The influence of the common bacterium Escherichia coliform (E. coli) on the nucleation and growth of calcium oxalate (CaOxa) in aqueous solution is studied in order to determine its role in the biomineralization of urinary stones. The results show that CaOxa crystals obtained in the presence of E. coli transform more quickly from calcium oxalate dihydrate (COD) into calcium oxalate monohydrate (COM), and they become even larger, than in the absence of the bacterium. On decreasing the concentration of chemical reagents, in other words increasing the ratio bacterium/CaOxa, except for the more rapid phase transition from COD to COM, the CaOxa particles obtained become larger and more regular with a hexagonal morphology. This suggests that E. coli accelerates the crystallization of COM, which is the most stable crystal phase of CaOxa and the major component of urinary stones. Transmission electron microscopy (TEM) images, electron diffraction (ED) patterns, and Fourier-transform IR (FTIR) spectra show that the biomineralization process of CaOxa crystals takes place both inside and outside the bacterium, which implies that it is induced by both intracellular biomolecules and the bioorganic secretions of the bacteria. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) data and UV/Vis spectra show that the proteins bound to the crystal surface with a molecular weight of around 26.5 kDa have tyrosine, tryptophan, or phenylalanine residues. The zeta potential and FTIR spectra are used to investigate the mineralization mechanism of CaOxa with E. coli and show that, the negatively charged biomolecules inside and outside the bacterium interact with Ca2+ ions to provide nucleation sites and then act as modifiers to induce the nucleation, growth, and aggregation of COM crystals. Therefore, we infer that E. coli mineralizes calcium oxalate and plays a role in the formation of urinary stones.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The Role of Escherichia coliform in the Biomineralization of Calcium Oxalate Crystals

Unusual rhombohedral strontium carbonate (SrCO3) aggregates have been synthesized in situ from strontium nitrate by the slow release of carbon dioxide by alkaline hydrolysis of diethyl carbonate at the water/hexamethylene interface in the presence of cetyltrimethylammonium bromide (CTAB). Transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray powder diffractometry were used to characterize the products. The results indicate that rhombohedral SrCO3 aggregates are obtained with weaker crystallinity and sizes of several micrometers. The possible formation mechanism of the SrCO3 aggregates at the interface is discussed, which can be interpreted by particle-aggregation based non-classical crystallization laws. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Qingfeng Zhang

Papers

Green synthesis of silver nanoparticles using Capsicum annuum L. extract

Size- and Shape-Controlled Synthesis and Assembly of a Silver Nanocomplex in UV-Irradiated TSA Solution

The Role of Escherichia coliform in the Biomineralization of Calcium Oxalate Crystals

Synthesis of rhombohedral strontium carbonate aggregates at the water/hexamethylene interface with cetyltrimethylammonium bromide

A novel biological strategy for morphology control of PbWO4 crystals in tomato extract.