Nanoparticulas

8546

Langmuir 2005, 21, 8546-8553

Comparative Study of the Morphology, Aggregation, Adherence to Glass, and Surface-Enhanced Raman Scattering Activity of Silver Nanoparticles Prepared by Chemical Reduction of Ag+ Using Citrate and Hydroxylamine
M. V. Canamares,† J. V. Garcia-Ramos,† J. D. Gomez-Varga,‡ C. Domingo,† and ˜ ´ S. Sanchez-Cortes*,†
Instituto de Estructura de la Materia, CSIC,Serrano 121, and Instituto de Ciencia y Tecnologıa de Polımeros, CSIC, Juan de la Cierva 3, 28006-Madrid, Spain ´ ´ Received January 5, 2005. In Final Form: June 13, 2005
Two different silver colloids were prepared by chemical reduction of silver nitrate with trisodium citrate and hydroxylamine hydrochloride to compare their characteristics in relation to their possible use in surface-enhancedRaman scattering (SERS) spectroscopy. The morphology and plasmon resonance of the single nanoparticles and aggregates integrating these colloids were characterized by means of UV-vis absortion spectroscopy and scanning electron microscopy, revealing important differences between each type of nanoparticle as concerns their physical properties. These metallic systems also manifested differences inthe aggregation and the adherence to glass surfaces, revealing significant differences in the chemical surface properties of these nanoparticles. SERS and surface-enhanced IR also indicated the presence of interference bands which can overlap the spectra of the analyte, mainly in the case of the citrate colloid. All these differences have an important influence on the applicability of thesenanostructured systems in SERS. In fact, the enhancement factor and spectral pattern of the SERS obtained by using alizarin as a molecule probe are different.

Introduction Surface-enhanced Raman scattering (SERS) represented a great advance in the field of Raman spectroscopy during the 1970s since the inherent weakness of the Raman signal can be substantially increased by 6 or more orders ofmagnitude. SERS is based on the huge enhancement of Raman emission of certain molecules when they are placed in the proximities of certain rough metal surfaces.1,2 This technique can be successfully applied in the study of poorly soluble compounds in water, since very low concentrations are required, with the additional advantage of the fluorescence quenching occurring on the metal surface.3,4 The useof SERS in analytical studies strongly depends on the optical and electrical characteristics of the nanostructured metal employed as substrate. During the past few decades many different methods have been proposed in the preparation of metal nanostructured substrates valid for SERS.5-16 Among these substrates, colloidal nanoscale particles have been the most frequently used.
* To whomcorrespondence should be addressed. Fax: +34 91 5 64 55 57. Phone: +34 91 5 61 68 00. E-mail: imts158@ iem.cfmac.csic.es. † Instituto de Estructura de la Materia. ‡ Instituto de Ciencia y Tecnologıa de Polımeros. ´ ´
(1) Moskovits, M. Rev. Mod. Phys. 1985, 57, 783. (2) Wokaun, A. Mol. Phys. 1985, 56, 1. (3) Hildebrandt, P.; Stockburger, M. J. Phys. Chem. 1984, 88, 5935. (4) Jancura, D.; Sanchez-Cortes,S.; Kocisova, E.; Miskovsky, P.; Tinti, A.; Bertoluzza, A. Biospectroscopy 1995, 1, 265. (5) Creighton, J. A.; Blatchford, C. G.; Albrecht, M. G. J. Chem. Soc., Faraday Trans. 2 1979, 75, 790. (6) Sapieszko, R. S.; Matijevic, E. J. Colloid Interface Sci. 1980, 74, 405. (7) Lee, P. C.; Meisel, D. J. Phys. Chem. 1982, 86, 3391. (8) Ni, F.; Cotton, T. M. Anal. Chem. 1986, 58, 3159. (9) Curtis, A. C.;Duff, D. G.; Edwards, P. P.; Jefferson, D. A.; Johnson, B. F. G:; Kirkland, A. I.; Wallace, A. S. J. Phys. Chem. 1988, 92, 2270.

Metal colloids, in particular Ag and Au, were first used as substrates in SERS by Creighton et al.5 Among the possible metals with applications in SERS (Ag, Au, and Cu), silver is the more universal substrate for several reasons: broad plasmon resonance in the...