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 nanoparticle applications and human health

We report the results of a 28-day oral exposure study in rats, exposed to <20 nm noncoated, or <15 nm PVP-coated silver nanoparticles ([Ag] = 90 mg/kg body weight (bw)), or AgNO3 ([Ag] = 9 mg/kg bw), or carrier solution only. Dissection was performed at day 29, and after a wash-out period of 1 or 8 weeks. Silver was present in all examined organs with the highest levels in the liver and spleen for all silver treatments. Silver concentrations in the organs were highly correlated to the amount of Ag+ in the silver nanoparticle suspension, indicating that mainly Ag+, and to a much lesser extent silver nanoparticles, passed the intestines in the silver nanoparticle exposed rats. In all groups silver was cleared from most organs after 8 weeks postdosing, but remarkably not from the brain and testis. Using single particle inductively coupled plasma mass spectrometry, silver nanoparticles were detected in silver nanoparticle exposed rats, but, remarkably also in AgNO3 exposed rats, hereby demonstrating the forma...

Distribution, Elimination, and Toxicity of Silver Nanoparticles and Silver Ions in Rats after 28-Day Oral Exposure

Silver nanoparticles induce oxidative cell damage in human liver cells through inhibition of reduced glutathione and induction of mitochondria-involved apoptosis

Background
Zinc oxide nanoparticles (ZnO NPs) have received much attention for their implications in cancer therapy. It has been reported that ZnO NPs induce selective killing of cancer cells. However, the underlying molecular mechanisms behind the anticancer response of ZnO NPs remain unclear.

http://fac.ksu.edu.sa/sites/default/files/5_0.pdf

Zinc oxide nanoparticles selectively induce apoptosis in human cancer cells through reactive oxygen species.

Silver nanoparticles induced heat shock protein 70, oxidative stress and apoptosis in Drosophila melanogaster.

Differential toxicity of silver and titanium dioxide nanoparticles on Drosophila melanogaster development, reproductive effort, and viability: size, coatings and antioxidants matter.

Inhalation method for delivery of nanoparticles to the Drosophila respiratory system for toxicity testing.

Nanoparticles (NPs) are a growing facet of our
industrial, medical and environmental economy Toxicity research
has focused on acute exposures both in vitro and in vivo Few in
vivo studies on chronic lifetime effects of NP exposure are
available Drosophila melanogaster provides a powerful model for
investigating human health and nanotoxicity Counterparts of genes
responsible for more than 700 different human genetic diseases,
including neurological, immunological, cardiovascular, auditory,
visual, developmental and metabolic disorders, are found in
Drosophila (Koh et al 2006; Wolf et al 2006; Rieter et al 2001,
Sykiotis and Bohmann 2008) The cost effectiveness, experimental
flexibility, and short generation time of Drosophila permit rapid
assessment of the vast number of NPs being produced, including
chronic and reproductive effects, thus providing a first tier
assessment We have developed an in vivo chronic nanotoxicity model
using Drosophila melanogaster The effects of different
nanoparticles (silver and titanium) exposure on Drosophila
reproduction, development, and survivorship, were assessed based on
different sizes, and coatings We’ve found that chronic exposure to
silver NPs via ingestion has toxic effects on fly viability and
reproductive effort Conversely, titanium oxide has no effect on
fly life history, and serves to verify the ability of our model to
discriminate among nanoparticle toxicity We also demonstrate the
reversal of NP silver toxicity through diet supplementation with
vitamin C By including vitamin C in NP treated fly food, the flies
were protected from the toxic life history effects of nanosilver
ingestion This corroborates previous results that implicate
oxidative stress as the primary contributor to silver toxicity and
provides a potential antioxidant-based strategy for the development
of prophylactics to NP exposure

Ryan Posgai

Papers

Silver nanoparticles induced heat shock protein 70, oxidative stress and apoptosis in Drosophila melanogaster.

Differential toxicity of silver and titanium dioxide nanoparticles on Drosophila melanogaster development, reproductive effort, and viability: size, coatings and antioxidants matter.

Inhalation method for delivery of nanoparticles to the Drosophila respiratory system for toxicity testing.

Development of a Drosophila melanogaster model system for nanoparticle toxicity assessment