Preparation and characterization of uniform-sized chitosan/silver microspheres with antibacterial activities

摘要

The chitosan/silver microspheres (CAgMs),which possess effective inhibitory onmicroorganisms,were prepared by an inverse-emulsification cross-linking method using CS/Ag sol as dispersed phase, whiteruss as continuous phase, and glutaraldehyde as crosslinking agent. The size and shape of CAgMs, greatly affecting their antibacterial activities,were controlled by varying the concentrations of cross-linking agent, emulsifier and CS/Ag colloid. The preparation conditions for obtaining uniform-sized microspheres were optimized. The morphology of CAgMs was characterized by scanning electron microscopy (SEM) and laser particle size analysis. The spherical CAgMs with smooth surface in the mean size of ca. 5 μm exhibited a narrowparticle size distribution. Energy Dispersive X-ray spectroscopy (EDX) revealed the elemental composition of the microspheres. Transmission electron micrographs (TEM) and Fourier transform infrared spectroscopy (FTIR) of the microspheres confirmed the formation of silver nanoparticles (AgNPs). The X-ray diffraction (XRD) patterns and UVVisible diffuse reflectance spectroscopy (UVvis DRS) of the sample showed that AgNPs with the diameter no more than 20 nm were face-centered cubic crystallites. X-ray photoelectron spectroscopy (XPS) proved that AgO bond existed in the microspheres. Thermogravimetric analysis (TGA) showed that the starting decomposition temperature of CAgMs (ca. 260 °C) was much higher than that of CS (ca. 160 °C), suggesting that the as-prepared CAgMs possessed better thermal stability than original CS did. Antimicrobial assayswere performed using typical Grambacteria and fungi. The inhibitory effect indicated that the as-prepared microspheres exerted a stronger antibacterial activity as the concentration of the AgNPs is increasing, and themicrospheres in smaller size hadmuch better antibacterial activity than those in the larger size. The antimicrobial mechanism of CAgMs was discussed.