An investigation on effect of capping agent on silver nanoparticles antibacterial activity

Silver nanoparticles (Ag NPs) are receiving much attention due to their various physical, chemical and antimicrobial properties. The aim of this study is to synthesize the Ag NPs using various capping agents ("B-cyclodextrin, starch, sodium citrate and chitosan") and investigate the effective capped Ag NP, based on their particle size, stability and antibacterial properties against a range of gram positive and gram negative bacteria (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus mesentericus). This will contribute to further understanding the effects of capping agents on how they can improve stability and properties of Ag NPs as well as help determine their potential for future application as an alternative treatment to antibiotics against multidrug resistant bacteria. The capped Ag NPs were characterized by UV-Vis spectroscopy, FTIR and DLS.The UV-Vis spectra exhibited an absorption band between 400-430 nm for all capped Ag NPs, indicating colloidal spherical shapped Ag NPs. Amongst all the synthesized capped Ag NPs, greater stability was achieved by the sodium citrate capped Ag NPs (SC-Ag NPs) until six weeks.The smallest particle size was observed for chitosan capped silver nanoparticle (CH-Ag NPs) and both chitosan capped Ag NPs and sodium citrate capped Ag NPs (SC-Ag NPs) proved to be the most effective capping agents in terms of antibacterial activities with CHAg NPs consistently displaying the strongest and broadest antibacterial activity against all tested bacteria followed by SC-Ag NPs. Conclusively, the influence of capping agents on Ag NPs was seen to better stabilize Ag NPs to varying degrees and enhance their antibacterial activity when compared to uncapped Ag NPs.