In recent years, there has been a marked interest in the study and use of chemical, electronic, optical and magnetic properties of metal nanoparticles (Nps) [1]. Among the highlights include research concerning the synthesis and characterization of physical and chemical properties [2]; application in nanostructures [3], clinical diagnosis, as markers for biomolecules [4] and more recently in therapeutic applications such as drug liberation and radiotherapy or hiperthermic treatments [5]. Moreover, the excellent electronic properties of the metal Nps make them very attractive for the development of electrical devices [6] and for its applications in molecular catalysis [7] and in sensors and biosensors [8-10]. The incorporation of Nps in organized molecular structures is crucial to develop new materials technologically useful. The Nps assembly in bi-or three-dimensional structures was described through different methodologies, between them the electrostatic adsorption with polyelectrolytes of opposite charge. The final properties of the structures formed, such as charge density, permeability, conductivity, and optical characteristics are highly dependent on the morphology of the Nps and conditions of adsorption [11]. The objective of this work was to build and characterize self assembled structures of gold nanoparticles (gNP) and the polymer chitosan and to evaluate the consequence of the nanoparticles size, the adsorption time, and the structural characteristic of the polymer in the optical response. Commercial and chemically modified chitosan and citrate stabilized gold nanoparticles were self assembled on to a quartz surface, and then spectral curves were collected in the presence of buffer solution. The effect of the Nps adsorption time was explained using effective medium theory. In the case of gold nanoparticles with 10 nm of diameter, coupling between nanoparticles was not observed below the saturation coverage, while a clear interaction between particles was evident for 20 nm diameter particles, even under lowest coverage degree. For the multilayers, the interaction between particles in adjacent bilayers was evaluated taking in to account the electromagnetic coupling between particles. The effect of the polymer structure, specially its charge density was also analyzed.
References: 1) S. Eustis, M. A. El-Sayed, Chem. Soc. Rev., 2006, 35, 209.2) M. Ch. Daniel, D. Astruc, Chemical Reviews, 104, 1, 2004,293. 3) A. Escorcia, A. Dhirani, Journal of Electroanalytical Chemistry, 601, 2007, 260. 4) C. S. Thaxton, D. G. Georganopoulou,
