Silver nanoparticles have antimicrobial properties and their biological activity has been attributed to the release of silver ions and/or oxidative reactions on the particle surface. There is, therefore, a significant interest in optimizing their formulation for performance and safety. Now, in a systematic study, Robert Hurt and colleagues at Brown University show that the biological activity of silver nanoparticles can be tuned by controlling the release of soluble silver ions from their surface using different chemical approaches.
Hurt and colleagues examined whether ion release can be controlled by manipulating the particle size or surface, the availability of oxidants, and the composition of the surrounding media. It was found that release of ions can be slowed down by binding ligands (such as thiols and citrate) or creating a sulphidic coating on the surface to prevent the access of oxygen, or by scavenging reactive oxygen intermediates from the surrounding medium using enzymes. Preoxidizing the nanoparticles with dry ozone or reducing the size of the particles can enhance the release of ions. The different formulations tested on a bacterial inhibition assay confirmed that the biological activity of silver nanoparticles can be fine-tuned according to the desired application.
This controlled-release approach offers a way to manage the dose for optimum bactericidal effects or release profile in biomedical applications, to limit toxicity, and to control the lifetime of products containing silver nanoparticles.