Optical Enhancing Properties in Layer-by-Layer Films of Dendrimer and Gold Nanoparticles David S. dos Santos Jr., 1 Rafaela C. Sanfelice, 2 Ramon Alvarez-Puebla, 1 Osvaldo N. Oliveira Jr., 2 Ricardo F. Aroca * 1 Summary: Portable multilayer films containing gold nanoparticles embedded in a dendrimer matrix have been fabricated using the layer-by-layer (LbL) technique, characterized and tested for applications in surface-enhanced Raman scattering (SERS). Film formation was monitored by microgravimetry measurements using a quartz crystal microbalance (QCM) and UV-visible spectroscopy. The surface morphology was investigated with atomic force microscopy (AFM) measurements. SERS was recorded for 2-Naphtalenethiol(NFT) cast onto the LbL film and the results show that the optical enhancing ability is a function of the number of bilayers. The analytes show an increase of SERS effect that follows the surface roughness, being stabilized after a certain number of bilayers are deposited. Keywords: composites; dendrimer; layer-by-layer; Raman spectroscopy; SERS Introduction Surface-enhanced spectroscopy benefits from optical enhancement assisted by sur- face plasmon excitations in metallic nano- particles. [1–3] For ultrasensitive chemical analysis, the most successful enhancing substrates in surface-enhanced Raman scat- tering (SERS) are gold and silver nano- structures. [4,5] The latter have been fabricated using a variety of physical and chemical methods, such as evaporation of metal, electrochemical roughening of metal electro- des, and lithographic techniques. [6,7] In the fabrication of nanostructured materials the main challenge is the control of the size and shape of nanoparticles in order to achieve specific physical properties. In addition to size and shape control, for some practical applications it is advantageous to produce films that can be used as substrates or port- able sensors for spectrochemical analysis. [8,9] In this context, we and others are exploiting the chemical methods using the layer-by- layer (LbL) technique. LbL films are pro- duced by alternating the immersion of a substrate in cationic and anionic solutions, usually polyelectrolytes. These films can be viewed as dense, stratified hydrogels made of polyelectrolyte layers and with a certain degree of interpenetration. In this model, the cross-linking density, or mesh size, is con- trolled by the charge distribution along the chain. The formation of LbL films is not restricted to polyelectrolyte pairs; it has been applied to polymer/proteins, polymer/cera- mics and polymer/metals. [10,11] A number of external parameters, which can be varied during the deposition process, are known to influence the resulting layer structure. These include the ionic strengh of the deposition solutions, the polyion concentration, the charge density of the polyion and the mole- cular weight. The exact control of these factors can generate surfaces with specific properties. Included in the materials that are particularly well suited for use in LBL films are dendrimers. [12] In contrast to conven- tional polymers, dendrimers have precisely controlled structures, molecular weights, and chemical functionalities. They have been employed as stabilizers in the synthesis of Macromol. Symp. 2006, 245–246, 325–329 DOI: 10.1002/masy.200651344 325 1 Materials & Surface Science Group, Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada, N9B 3P4 2 Instituto de Fı´sica de Sa ˜ o Carlos, Universidade de Sa ˜o Paulo,Sa ˜o Carlos -SP, 13560-970, Brazil Copyright ß 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim