Neutrally charged nanosilver antimicrobial effects: A surface thermodynamic perspective

Nanosilver (AgNP) has a large surface area that contributes to enhanced interactions with bacteria, as well as silver ion release. The actual AgNP antimicrobial effect is determined by the AgNP size. AgNPs with smaller diameters showed better antimicrobial effects because smaller AgNPs had larger surface areas, which led to greater silver ion release and stronger attachment to bacteria. The attachment of AgNPs to bacterial surfaces is attributed to the attractive interactions between the AgNPs and bacteria, which is also a function of the size of AgNPs. Although the antimicrobial activity of AgNPs has been extensively studied, there is a gap between antimicrobial effects of AgNPs on bacteria and their subsequent attachment. To fully understand the antimicrobial effectiveness of different-sized AgNPs, this study investigated the dynamic process of AgNP-bacteria interactions in aqueous media, including AgNP aggregation, AgNP attachment, and antimicrobial effects. AgNP-AgNP and AgNP-bacteria interactions were quantified based on DLVO and surface chemistry theories, which were used to interpret subsequent AgNP aggregation, AgNP-bacteria attachment and AgNP antimicrobial observations. [Display omitted] •Antimicrobial effects of nanosilver were affected by the nanosilver size.•Besides nanosilver size, bacterial strain also played an important role.•Interfacial surface energy was affected by the nanosilver size.•Smaller nanosilver leaded to a smaller repulsion interaction.•Rhamnolipid enhanced antimicrobial effects by increasing interfacial energy.