Surface Charge-Dependent Toxicity of Silver Nanoparticles

TLDR

Silver nanoparticles are widely used, raising environmental concerns, and their toxicity has been linked to size, shape, and capping, with purification steps often omitted in studies. The study examined how surface charge influences AgNP toxicity by testing four nanoparticles with different charge states. Four AgNPs—uncoated H₂, citrate‑coated, PVP‑coated, and BPEI‑coated—were purified by ultrafiltration and then exposed to bacterial species. The results show that AgNP toxicity varies with surface charge, with positively charged particles exhibiting higher toxicity toward the tested bacillus species.

Abstract

As a result of the extensive number of applications of silver nanoparticles (AgNPs), their potential impacts, once released into the environment, are of concern. The toxicity of AgNPs was reported to be dependent on various factors such as particle size, shape and capping agent. Although these factors may play a role in AgNPs toxicity, the results presented herein suggest that surface charge is one of the most important factors that govern the toxicity of AgNPs. In the current study, the toxicity of four AgNPs representing various surface charging scenarios ranging from highly negative to highly positive was investigated. These AgNPs were (1) uncoated H(2)-AgNPs, (2) citrate coated AgNPs (Citrate-AgNPs), (3) polyvinylpyrrolidone coated AgNPs (PVP-AgNPs), and (4) branched polyethyleneimine coated AgNPs (BPEI-AgNPs). Our results clearly demonstrate that the AgNPs exhibited surface charge-dependent toxicity on the bacillus species investigated. Furthermore, ultrafiltration membranes were utilized to purify the AgNPs suspensions from residual impurities prior to the introduction to the microbes. This step was crucial in determining the true AgNPs toxicity and is either missing or not explicitly mentioned in most of the reported toxicity studies.