Chitosan Thin Films on Glass and Silicon Substrates

Chitosan is an interesting polysaccharide, which can be easily derived from chitin by deacetylation. Chitin is widely found in nature as a major component of the cell wall of shells of insects and crustaceans, among other animal or even botanic species. The most distinguishing chitosan properties are its biodegradability, biocompatibility and its solubility in aqueous solutions, which makes it a “green” polymer [1]. Hybrid systems formed by inorganic substrates functionalized with organic molecules are experiencing a vast development, with many applications for chemical and biochemical sensing. The difficulty of chemically modifying inorganic surfaces can be overcome through the use of ultrathin organic films, as chitosan films. Besides their ability to protect the surface, the presence of an organic ultrathin layer opens the way to diversify the possibility of surface modification [2]. Control of both thickness and surface chemical composition of the covering film is required. Methods were developed for adsorbing the chitosan layer to glass and silicon substrates, depositing a uniform layer. Using chitosan with low molecular weight, from Aldrich, a 1 % wt chitosan acidic aqueous solution was prepared. It was completely dissolved and filtered. Silicon (100) from Siltronix and Glass slides, Corning glass, from Aldrich were used. Si substrates were etched using a multistep procedure which led to a hydrophilic surface [3]. Glass substrates were just degreased with acetone. The thin films of chitosan were prepared by spin-coating. Initially, some difficulty was experienced in obtaining adequate solutions of chitosan, without agglomerates. With the help of Light Scattering measurements and a sequence of filtrations, a uniform, agglomerates-free solution was obtained, which yielded transparent films.