Preparation of size-controlled silver nanoparticles and chitosan-based composites and their anti-microbial activities

We previously reported a simple method for the preparation of size-controlled spherical silver nanoparticles (Ag NPs) generated by autoclaving a mixture of silver-containing glass powder and glucose. The particle size is regulated by the glucose concentration, with concentrations of 0.25, 1.0 and 4.0 wt% glucose providing small (3.48 +/- 1.83 nm in diameter), medium (6.53 +/- 1.78 nm) and large (12.9 +/- 2.5 nm) particles, respectively. In this study, Ag NP/chitosan composites were synthesized by mixing each of these three Ag NP suspensions with a 75% deacetylated (DAc) chitosan suspension (pH 5.0) at room temperature. The Ag NPs were homogeneously dispersed and stably embedded in the chitosan matrices. The Ag NP/chitosan composites were obtained as yellow or brown flocs. It was estimated that approximately 60, 120 and 360 mu g of the small, medium and large Ag NPs, respectively, were maximally embedded in 1 mg of chitosan. The bactericidal and anti-fungal activities of the Ag NP/chitosan composites increased as the amount of Ag NPs in the chitosan matrix increased. Furthermore, smaller Ag NPs (per weight) in the chitosan composites provided higher bactericidal and anti-fungal activities.