FT-Raman and surface-enhanced Raman scattering (SERS) spectroscopy were applied in the vibrational characterization and study of the adsorption and acidity behavior of the highly fluorescent anthraquinone dye alizarin on Ag colloids prepared by chemical reduction with hydroxylamine hydrochloride. The SERS spectra were obtained at different conditions of pH, excitation wavelength and pigment concentration in order to deduce the adsorption mechanism of this molecule. On the basis of the results found we propose an adsorption model for alizarin, which has a different acidic behavior on the metal surface to that in solution. On the metal the deprotonation order of the OH groups changes with respect to the aqueous solution, the OH in position 1 being the first to be ionized instead of that in position 2 as occurs in solution. The two main alizarin forms identified on the metal surface correspond to the mono-and dianionic alizarin species.

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-enhanced Raman 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 in the 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 these nanostructured systems in SERS. In fact, the enhancement factor and spectral pattern of the SERS obtained by using alizarin as a molecule probe are different.

Ag-coated Au and Au-coated Ag colloidal particles were prepared by deposition of Ag or Au through chemical reduction on Au or Ag colloids, respectively. Different amounts of the depositing metal were employed in order to obtain different compositions of the Au100-xAgx and Ag100-yAuy resulting particles. The obtained colloids were characterized by UV-vis spectroscopy and transmission electron microscopy. A different formation mechanism was deduced for the different mixed colloids obtained by this procedure. Moreover, the activity of these colloids in surface-enhanced Raman spectroscopy (SERS), that is, the SERS enhancement factor, was checked by using pyridine as an adsorbate probe. The SERS excitation profiles for each colloid were investigated in order to obtain information about the activity of these substrates at different excitation wavelengths as well as to estimate the relative exposed area of each metal in every composite colloid.