The Effect of Charge at the Surface of Silver Nanoparticles on Antimicrobial Activity against Gram‐Positive and Gram‐Negative Bacteria: A Preliminary Study

TLDR

Silver nanoparticles’ antibacterial efficacy has been studied for charged variants, yet neutral charge effects remain unexplored. This study aims to assess how surface charge of silver nanoparticles influences antibacterial activity against selected bacteria. Three silver nanoparticles with positive, neutral, and negative surface charges were synthesized and their antibacterial activity against gram‑positive and gram‑negative bacteria was evaluated using well‑diffusion and micro‑dilution assays. Results showed positively charged nanoparticles exhibited the strongest bactericidal effect, negative the weakest, and neutral intermediate; Proteus vulgaris was the most resistant, and surface charge significantly influenced antibacterial activity, with neutral particles still effective against most species.

Abstract

The bactericidal efficiency of various positively and negatively charged silver nanoparticles has been extensively evaluated in literature, but there is no report on efficacy of neutrally charged silver nanoparticles. The goal of this study is to evaluate the role of electrical charge at the surface of silver nanoparticles on antibacterial activity against a panel of microorganisms. Three different silver nanoparticles were synthesized by different methods, providing three different electrical surface charges (positive, neutral, and negative). The antibacterial activity of these nanoparticles was tested against gram‐positive (i.e., Staphylococcus aureus , Streptococcus mutans , and Streptococcus pyogenes ) and gram‐negative (i.e., Escherichia coli and Proteus vulgaris ) bacteria. Streptococcus mutans , and Streptococcus pyogenes ) and gram‐negative (i.e., Escherichia coli and Proteus vulgaris ) bacteria. Well diffusion and micro‐dilution tests were used to evaluate the bactericidal activity of the nanoparticles. According to the obtained results, the positively‐charged silver nanoparticles showed the highest bactericidal activity against all microorganisms tested. The negatively charged silver nanoparticles had the least and the neutral nanoparticles had intermediate antibacterial activity. The most resistant bacteria were Proteus vulgaris . We found that the surface charge of the silver nanoparticles was a significant factor affecting bactericidal activity on these surfaces. Although the positively charged nanoparticles showed the highest level of effectiveness against the organisms tested, the neutrally charged particles were also potent against most bacterial species.