Evaluation of the toxicities of silver and silver sulfide nanoparticles against Gram‐positive and Gram‐negative bacteria

In this study, the endogenous lipid signalling molecules, N ‐myristoylethanolamine, were explored as a capping agent to synthesise stable silver nanoparticles (AgNPs) and Ag sulphide NPs (Ag(2) S NPs). Sulphidation of the AgNPs abolishes the surface plasmon resonance (SPR) maximum of AgNPs at 415 nm with concomitant changes in the SPR, indicating the formation of Ag(2) S NPs. Transmission electron microscopy revealed that the AgNPs and Ag(2) S NPs are spherical in shape with a size of 5–30 and 8–30 nm, respectively. AgNPs and Ag(2) S NPs exhibit antimicrobial activity against Gram‐positive and Gram‐negative bacteria. The minimum inhibitory concentrations (MIC) of 25 and 50 μM for AgNPs and Ag(2) S NPs, respectively, were determined from resazurin microtitre plate assay. At or above MIC, both AgNPs and Ag(2) S NPs decrease the cell viability through the mechanism of membrane damage and generation of excess reactive oxygen species.