Enhancement of the antibacterial properties of silver nanoparticles using β-cyclodextrin as a capping agent

Silver nanoparticles (AgNPs) were synthesised by reducing silver salts using NaBH4 followed by capping with varying concentrations of β-cyclodextrin (β-CD) and were physically characterised. Antibacterial activity against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus was determined by a microtitre well method. The AgNPs were spherical under transmission electron microscopy, whilst dynamic light scattering showed average diameters of capped particles to be smaller (4–7 nm) than their uncapped equivalents (17 nm). Capped particles demonstrated superior photostability when exposed to intense ultraviolet radiation for 4 h as well as significantly (P < 0.05) higher (up to 3.5-fold) antibacterial activity. The influence of β-CD concentration was seen to delay bacterial growth, indicating that a Trojan horse mechanism may be occurring owing to bacterial carbohydrate affinity, thereby enhancing silver ion absorption.