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Metal nanoparticle-chitosan (NPs-chitosan) bioconjugates were formed by exposure of chitosan to an aqueous solution of metal salts under thermal treatment. The metal nanoparticles that are formed strongly bound to chitosan, which encouraged us to investigate their catalytic performance. It was demonstrated that the metal NPs-chitosan bioconjugates functioned as effective catalysts for the reduction of 4-nitrophenol in the presence of NaBH(4), which was monitored by means of spectrophotometry as a function of reaction time. The silver NPs-chitosan bioconjugates exhibited excellent catalytic activity and were reusable for up to seven cycles. In contrast, the gold NPs-chitosan catalyst displayed poor catalytic activity, even in the second cycle. A highlight of our approach is that chitosan simultaneously acts as an active support for the synthesis and assembly of nanoparticles, and the resultant bioconjugates bear the advantage of easy separation from the reaction medium., (Copyright 2009 Elsevier Ltd. All rights reserved.)

Chitosan-based silver nanoparticles were synthesized by reducing silver nitrate salts with nontoxic and biodegradable chitosan. The silver nanoparticles thus obtained showed highly potent antibacterial activity toward both Gram-positive and Gram-negative bacteria, comparable with the highly active precursor silver salts. Silver-impregnated chitosan films were formed from the starting materials composed of silver nitrate and chitosan via thermal treatment. Compared with pure chitosan films, chitosan films with silver showed both fast and long-lasting antibacterial effectiveness against Escherichia coli. The silver antibacterial materials prepared in our present system are promising candidates for a wide range of biomedical and general applications.

Chitosan has natural abundance, unique bioactivity and attractive physicochemical properties. Recent years, the synthesis of chitosan-based metal nanomaterials has attracted increasing attention. The synthesis of metal nanoparticles utilizing biomolecular or organism offers a mild medium, and thus a greater degree of control over the nanoparticles produced, along with higher reproducibility. In particular, preparation of metal nanoparticles based on biomolecular or organism has its unique facility in integrating "minimum feature sizes" into labile biological components to an excellent synergy and bifunctional effect and consequently a more broad application. Herein, we review the new development of chitosan, chitosan-based synthesis of metal nanomaterials, and their application.

We present here a facile route to in-situsynthesis of free-standing metal (gold or silver) nanoparticles-embedded chitosan films by thermal treatment. The produced nanoparticles were confirmed by UV-vis spectroscopy and transmission electron microscopy (TEM). Interestingly, an exquisite dendritic structure was observed in the resulting silver-chitosan film, which was not present in pure chitosan and gold-chitosan samples. We speculated that the formation of dendritic structures may be due to the presence of nano-sized silver particles which has an influence on the crystallization behavior and thereby the morphology of biopolyer chitosan. The application of the as-prepared metal-chitosan films in surface-enhanced Raman spectroscopy (SERS) was investigated by using Rhodamine 6G (R6G) as probe molecules. It was found that the resultant metal-chitosan samples, especially silver-chitosan one, could be used as SERS substrates exhibiting excellent enhancement ability.

We present here a facile route for the synthesis of crystal Ag and Au nanoparticles on the basis of chitosan as a mediator agent under quiescent conditions. The resulting Ag nanoparticles displayed controllable structural and optical properties depending on the experimental parameters. Fourier transform infrared (FTIR) study combined with zeta potential measurement disclosed that the amino groups were bound to the particles, which was accountable for the stability of nanoparticles. The Ag and Au nanoparticles prepared in our present method is a promising candidate for applications in catalysis, antimicrobial and surface-enhanced Raman scattering.

A facile approach for the synthesis of chitosan-based Au nanostructures that have interesting absorptions in the near-infrared (NIR) region is presented. The effects of cooling treatment and the cross-linking agent glutaraldehyde on the formation of Au nanostructures based on chitosan were investigated. It has been demonstrated that the size and shape, and thus the optical properties of Au nanostructures, could be modulated via cooling treatment. The optical absorption extension of these Au nanostructures in the NIR region is promising in biomedical applications. The presence of a cross-linking agent, glutaraldehyde, during synthesis accelerated the reduction of the Au precursor and favored the growth of isotropic Au nanoparticles. A possible mechanism for the change in growth modality of Au nanostructures with and without glutaraldehyde was elucidated.

Single-crystal Au nanosheets with {111} planes as basal surfaces have been synthesized on the basis of the polysaccharide chitosan. The preferential adsorption of polar groups in chitosan molecules on {111} planes of Au nuclei may account for the formation of anisotropic nanosheets. Appropriate precursor (HAuCl(4)) concentrations are vital for the formation of Au nanosheets. The Au nanostructures thus prepared exhibit interesting shape-dependent optical properties. This convenient, environmentally friendly and low-cost route may be amenable to mass production.

Recent researches have largely been focused on chitosan, which is deacetylated chitin, the most abundant natural polysaccharide after cellulose. In this paper, we report the fabrication of gold nanoparticles (GNPs) by UV photoactivation in the presence of biopolymeric chitosan and the tracing of the gold salt solution aging. Detailed UV-visible spectroscopy study witnessed the evolution of the surface plasmon resonance (SPR) adsorption during the GNP growth. The effect of chitosan in aqueous solution for the GNP preparation was investigated in detail. The results indicated the size and distribution of GNPs could be controlled over by altering the concentration of chitosan, and the GNP growth during aging was a chitosan-mediated autocatalytic process. Fourier transform infrared spectroscopy (FTIR) showed the hydroxyl in molecular chitosan was oxidized to carbonyl groups in the fabrication of GNPs after aging and nitrogen atoms are the main sites for the complexation of chitosan with Au atoms. Our synthesis method in the present way can be used to form self-assemble monolayers of GNPs and fabricate biosensors based on surface plasmon resonance effect.