Antimicrobial properties of nano-silver: A cautionary approach to ionic interference

Abstract

a b s t r a c tHypothesis: Metallic nanoparticles such as nano-silver have found many applications as alternative antimicrobials in recent years. However methods for determining their proposed antimicrobial activity have received little attention to date. The disk diffusion assay is commonly used as a demonstration of antimicrobial properties and is a regular feature in synthetic nanoparticle papers. The aim of this study was to assess its effectiveness in demonstrating the ''nanoparticle specific'' antimicrobial properties in the absence of ionic contributions from unreacted reducing agents and or impurities. Experiments: The disk diffusion assay was carried out on a range of silver nanoparticles, both in-house synthesised and commercially available, using Escherichia coli ATCC 25922 as a model organism. Results: Capped and purified nanoparticles show no antimicrobial activity despite claims to the contrary for this assay. Results will be discussed in terms of the need for researchers without a background in microbiology to understand the mechanism of antimicrobial action before choosing an assay. Also discussed is the importance understanding the physiochemical characteristics of when interpreting results. Finally the relevance of the results in terms establishing protocols for method development for 'nanoparticle specific' antimicrobial properties will also be considered.

Risk assessment of silver nanoparticles

“…[3] The notion has been overestimated that the NCS is a hazard to humans and higher animals based on the recent works on numerous toxicological data obtained in studies in vitro and in vivo [4]. In addition, the growing concern is caused by the possible consequences of entering Ag NPs into the environment as a part of various waste products.…”

Fabrication and Characterization of Antibacterial Polyurethane Acrylate-based Materials

“…Typically, the reducing agents provide the reduction reaction such as silver nitrate with a reducing agent like sodium borohydride in the presence of colloidal stabilizer. Sodium borohydride has been used with polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), sodium dodecyl sulfate (SDS), bovine serum albumin (BSA), citrate and cellulose as stabilizing agents 12,18,22 . In this paper, the fabrication of the photocured materials which contained silver nanoparticles (Ag-NPs) was studied on the properties of materials such as physical, mechanical and thermal properties, especially antibacterial activity.…”

Advances in the Experimental and Theoretical Understandings of Antibiotic Conjugated Gold Nanoparticles for Antibacterial Applications

“…However, there is a long list of nanomaterials which can be used as an antibacterial agent, includes silver nanoparticles, graphene oxide and its derivatives, ZnO nanoparticles, TiO 2 nanoparticles and so on, still, AuNPs are preferred because of their bio‐inertness, and easy surface functionalization with thiol, amino‐, carboxyl‐containing antibiotic molecules . Generally, AuNPs do not exhibit antibacterial property, but due to the presence of unreacted ligands or some ionic impurities, they act as an antibacterial agent . AuNPs can be made antibacterial by grafting hydrophobic molecules, antibacterial peptides, antibiotics and a molecule which makes the gold nanoparticles positively charged .…”