Immobilized silver nanoparticles enhance contact killing and show highest efficacy: elucidation of the mechanism of bactericidal action of silver

Abstract

Antimicrobial materials with immobilized/entrapped silver nanoparticles (AgNPs) are of considerable interest. There is significant debate on the mode of bactericidal action of AgNPs, and both contact killing and/or ion mediated killing have been proposed. In this study, AgNPs were immobilized on an amine-functionalized silica surface and their bactericidal activity was studied concurrently with the silver release profile over time. This was compared with similar studies performed using colloidal AgNPs and AgCl surfaces that released Ag ions. We conclude that contact killing is the predominant bactericidal mechanism and surface immobilized nanoparticles show greater efficacy than colloidal AgNPs, as well as a higher concentration of silver ions in solution. In addition, the AgNP immobilized substrate was used multiple times with good efficacy, indicating this immobilization protocol is effective for retaining AgNPs while maintaining their disinfection potential. The antibacterial surface was found to be extremely stable in aqueous medium and no significant leaching (∼1.15% of total silver deposited) of the AgNPs was observed. Thus, immobilization of AgNPs on a surface may promote reuse, reduce environmental risks associated with leaching of AgNPs and enhance cost effectiveness.

Antibacterial properties and toxicity from metallic nanomaterials

“…Two leading theories on the proposed mechanism suggest 1) a disruption of membrane functionality from an interaction between released Ag + ions and the cell membrane and 2) extensive cell membrane damage caused by the formation of reactive oxygen species (ROS) ultimately causing damage to the cell due to oxidative stress ( Figure 1). [24][25][26] In brief, the first mechanism suggests that Ag + ions released from AgNPs can bind with thiol groups (-SH) of proteins and enzymes found on the cellular surface, causing destabilization of the cellular membrane and a breakdown of the ATP synthesis pathway. AgNPs may then adhere to the membrane wall, causing holes through which they can later penetrate the bacteria and interact with intracellular components or proteins containing sulfur.…”

A Novel Silver Nanoparticles-based Sensing Probe for the Detection of Japanese Encephalitis Virus Antigen

“…When silanized glass slides were immersed into Ag NPs suspension, the color of glass slides turned from colorless to yellow tinted. Ag NPs were deposited onto the surfaces of glass slides (Figure 3(c)) as positively charged ammonium ions of APTES would attract negatively charged citrate stabilized Ag NPs onto the surfaces of glass slides via electrostatic forces (Agnihotri et al 2013;Rashid et al 2013). Figure 4 shows the FESEM micrographs of Ag NPs-deposited glass slides.…”

“…Figure 3 shows the schematic representation of the preparation of Ag NPs-deposited glass slides. Agnihotri et al (2013) suggested that acid hydrolysis (Figure 3a) could generate uniform silanol groups (Si-OH) on the glass slides. Subsequently poly-condensation of APTES ( Figure 3(b)) took place for the formation of siloxane (Si-O-Si) bonds within the silanol sites on the glass surfaces and between aminosilane molecules during the heat treatment (Sharma et al 2012).…”

“…The silanized glass slides were then immersed in Ag NPs suspension for overnight to allow deposition of Ag NPs onto surfaces of glass slides. Ag NPs-deposited glass slides were rinsed with ultrapure water and dried at room temperature (Agnihotri et al 2013). …”

Facile and green fabrication of electrospun poly(vinyl alcohol) nanofibrous mats doped with narrowly dispersed silver nanoparticles

“…Smaller AgNPs bear stronger antibacterial properties, due to their larger surface area and faster silver ion release. 50,51 Recently, Agnihotri et al 52 reported immobilized or entrapped AgNPs on an amine-functionalized silica surface and studied their superior biocidal efficacy. Similarly, the AgNPs herein also show excellent antibacterial activities.…”