Surface-Enhanced Raman Scattering on Dendrimer/Metallic Nanoparticle Layer-by-Layer Film Substrates

• Published in: Langmuir Vol. 21; no. 12; pp. 5576 - 5581
• Main Authors: Goulet, Paul J. G, dos Santos, David S, Alvarez-Puebla, Ramón A, Oliveira, Osvaldo N, Aroca, Ricardo F
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 07.06.2005
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Atomic force microscopy; Amino group; Branched polymer; Film; Nanoparticle; Transition metal; Molecular size; Surface plasmon; Thin film; Aggregation; Characterization; Surface enhanced scattering; Chemical reduction; Substrate; Silver; Raman scattering; Optical properties; Nanocomposite; Dendritic structure
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la050202e

In this paper, the fabrication, characterization, and application of unique layer-by-layer (LBL) films of dendrimers and metallic nanoparticles is reported. Silver nanoparticles (d = ∼20 nm) are produced in solution by sodium citrate reduction and incorporated into thin films with generation 1 and 5 DAB−Am dendrimers (polypropylenimine dendrimers with amino surface groups) by the LBL technique. The resulting nanocomposite films are characterized by UV−visible surface plasmon absorption and atomic force microscopy (AFM) measurements, and employed as substrates for surface-enhanced Raman scattering (SERS) of 2-naphthalenethiol. Through variation of the molecular size (dendrimer generation) and concentration of the cross-linker used, as well as the number of layers produced, the optical properties of several different possible architectures are studied. In the films, Ag nanoparticles are shown to be effectively immobilized and stabilized with increased control over their spacing and aggregation. Moreover, the films are shown to be excellent substrates for SERS measurements, demonstrating significant enhancement capability. As expected, large electromagnetic enhancement of Raman scattering signals is found to be strongly dependent on interparticle coupling between neighboring metallic nanoparticles. Finally, the possibility of detecting SERS signals from architectures with intervening layers between the metal nanoparticles and analyte molecules is explored. It is shown that although there are decreases in intensity with increasing number of intervening layers (as is expected from the distance dependence of SERS), electromagnetic enhancement is still able to function at these distances, thus offering the possibility of developing sensors with external layers that are chemically selective for specific analytes.