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

The chitosan/silver microspheres (CAgMs), which possess effective inhibitory on microorganisms, 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 narrow particle 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 UV-Visible diffuse reflectance spectroscopy (UV-vis 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 assays were performed using typical Gram bacteria 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 the microspheres in smaller size had much better antibacterial activity than those in the larger size. The antimicrobial mechanism of CAgMs was discussed.

An J ，Ji Z ，Wang D ，Luo Q ，Li X ... -  《-》

Preparation, characterization and antibacterial activity of chitosan-g-poly acrylonitrile/silver nanocomposite.

Chitosan-grafted-poly acrylonitrile silver nanocomposites (Cs-g-PAN/Ag) were prepared via in-situ chemical reduction of Ag ions in graft copolymerization of acrylonitrile onto chitosan. Graft copolymerization process was provided by FTIR and gravimetric methods. UV spectra and TEM images show silver nanoparticles with average 15-20nm dispersed homogeneously in CS-g-PAN/Ag nanocomposite-ray and TGA evident the change in crystallography and thermal stability in consequence of presence Ag nanoparticles. Cs-g-PAN/Ag nanocomposite showed excellent antimicrobial performance towards bacteria such as Escherichia coli and Staphylococcus aureus.

Hebeish AA ，Ramadan MA ，Montaser AS ，Farag AM ... -  《-》

Antibacterial activity and mechanism of Ag-ZnO nanocomposite on S. aureus and GFP-expressing antibiotic resistant E. coli.

Emergence of multi-resistant organisms (MROs) leads to ineffective treatment with the currently available medications which pose a great threat to public health and food technology sectors. In this regard, there is an urgent need to strengthen the present therapies or to look over for other potential alternatives like use of "metal nanocomposites". Thus, the present study focuses on synthesis of silver-zinc oxide (Ag-ZnO) nanocomposites which will have a broad-spectrum antibacterial activity against Gram-positive and Gram-negative bacteria. Ag-ZnO nanocomposites of varied molar ratios were synthesized by simple microwave assisted reactions in the absence of surfactants. The crystalline behavior, composition and morphological analysis of the prepared powders were evaluated by X-ray diffraction, infrared spectroscopy, field emission scanning electron microscopy (FE-SEM) and atomic absorption spectrophotometry (AAS). Particle size measurements were carried out by transmission electron microscopy (TEM). Staphylococcus aureus and recombinant green fluorescent protein (GFP) expressing antibiotic resistant Escherichia coli were selected as Gram-positive and Gram-negative model systems respectively and the bactericidal activity of Ag-ZnO nanocomposite was studied. The minimum inhibitory concentration (MIC) and minimum killing concentration (MKC) of the nanocomposite against the model systems were determined by visual turbidity analysis and optical density analysis. Qualitative and quantitative assessments of its antibacterial effects were performed by fluorescent microscopy, fluorescent spectroscopy and Gram staining measurements. Changes in cellular morphology were examined by atomic force microscopy (AFM), FE-SEM and TEM. Finally, on the basis of the present investigation and previously published reports, a plausible antibacterial mechanism of Ag-ZnO nanocomposites was proposed.

Matai I ，Sachdev A ，Dubey P ，Kumar SU ，Bhushan B ，Gopinath P ... -  《-》

Synthesis and characterization of chitosan/ZnO nanoparticle composite membranes.

Novel chitosan/ZnO nanoparticle (CS/nano-ZnO) composite membranes were prepared via the method of sol-cast transformation and studied by UV-vis absorption spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray fluorescence spectrometry (EDX). The characterization revealed that ZnO nanoparticles dispersed homogeneously within the chitosan matrix. The mechanical and antibacterial properties of the product were investigated. The results showed that the ZnO content had an effect on the mechanical properties of CS/nano-ZnO composite membranes, and that the antibacterial activities of CS membranes for Bacillus subtilis, Escherichia coli, and Staphylococcus aureus were enhanced by the incorporation of ZnO. Further, CS/nano-ZnO composite membranes with 6-10 wt% ZnO exhibited high antibacterial activities.

Li LH ，Deng JC ，Deng HR ，Liu ZL ，Xin L ... -  《-》

A versatile effect of chitosan-silver nanocomposite for surface plasmonic photocatalytic and antibacterial activity.

Chitosan-silver (CS-Ag) nanocomposite was green synthesised without the aid of any external chemical-reducing agents. The synthesised nanocomposite was characterised by UV-visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HR-TEM) with selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), and zeta potential analyser. The particle size of the synthesised CS-Ag nanocomposite was around 20 nm and was found to be thermally stable in comparison with pure chitosan. The prepared nanocomposite acts as a photocatalyst for dye decolourisation, with a maximum of 81% of methyl orange (MO) decolourisation that occurred under visible light irradiation. The kinetics was found to follow pseudo-first-order according to Langmuir-Hinshelwood (L-H) model. The nanocomposite also proved to be an excellent antimicrobial agent against both Gram-positive and Gram-negative bacteria, possessing a broad spectrum of antimicrobial activity. The zone of inhibition ranged between 16.000 ± 1.000 and 19.333 ± 1.155 (mm), proving its high susceptibility than chitosan itself. The minimum inhibitory concentration (MIC) values were from 8 to 64 μg/mL, whereas the minimum bactericidal concentration (MBC) values ranged from 16 to 128 μg/mL, with the highest antibacterial activity shown against Gram-positive Staphlococcus aureus. This report illustrates the eco-friendly approach for the reduction of silver using chitosan as a reducing agent, and its potential to dye decay and microbial contaminants.

Nithya A ，JeevaKumari HL ，Rokesh K ，Ruckmani K ，Jeganathan K ，Jothivenkatachalam K ... -  《-》