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

Silver nanoparticles (AgNPs) were synthesised by reducing silver salts using NaBH(4) followed by capping with varying concentrations of beta-cyclodextrin (beta-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 4h as well as significantly (P<0.05) higher (up to 3.5-fold) antibacterial activity. The influence of beta-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.