Adsorption of chitosan onto carbonaceous surfaces and its application: atomic forcemicroscopy study

Abstract

The adsorption of chitosan onto highly ordered pyrolytic graphite(HOPG) surfaces and itsapplications have been studied by atomic force microscopy (AFM). The results indicatedthat chitosan topography formed on the HOPG surface significantly depends on the pHconditions and its concentration for the incubation. Under strongly acidic conditions (pH < 3.5) and at aconcentration of 1 mg ml − 1, chitosan formed into uniform network structures composed of fine chains.When the solution pH was changed from 3.5 to 6.5, chitosan tends to form athicker film. Under neutral and basic conditions, chitosan changed into sphericalnanoparticles, and their sizes were increased with increasing pH. Dendritic structureshave been observed when the chitosan concentration was increased up to 5 mg ml − 1. In addition, the chitosan topography can also be influenced by ionicstrength and the addition of different metal ions. When 0.1 M metal ionsNa + ,Mg2 + ,Ca2 + andCu2 + were added into the chitosan solution at pH 3.0 for the incubation, network structures,branched chains, block structures and dense networks attached with many small particleswere observed, respectively. The potential applications of these chitosan structures onHOPG have been explored. Preliminary results characterized by AFM and XPSindicated that the chitosan network formed on the HOPG surface can be used forAFM lithography, selective adsorption of gold nanoparticles and DNA molecules.