Adsorption of linear aliphatic α,ω-dithiols on plasmonic metal nanoparticles: a structural study based on surface-enhanced Raman spectra.

The adsorption mechanism of linear aliphatic α,ω-dithiols with chain lengths of 6, 8 and 10 carbon atoms on silver and gold nanoparticles has been studied by surface-enhanced Raman scattering (SERS) spectroscopy. SERS spectra provided the structural marker bands of these compounds and they were employed to obtain information about the adsorption and coordination mechanism, the orientation, conformational order, and packing of the aliphatic chains of dithiols on the metal nanoparticle surface. The effect of the type of metal (silver or gold) and the extent of surface coverage on all the above mentioned properties is discussed. It was found that the adsorption of dithiols on Au nanoparticles leads to a more disordered structure of the aliphatic chains of dithiols in comparison with the adsorption on Ag nanoparticles. The interaction through both thiol groups makes the adsorption of dithiols on metal surfaces substantially different from that of monothiols; in particular, the orientation of dithiols is perpendicular, while monothiols adopt a tilted orientation. Dithiols may act as linkers between metal nanoparticles and induce the formation of nanogaps with a controllable interparticle distance. The nanogaps thus formed are able to produce hot spots exhibiting a large intensification of electromagnetic field in these points which has been proved by the observation of intense SERS spectra of dithiols until a concentration of 10(-8) M, corresponding to a large Raman enhancement factor of 5 × 10(6).

Adsorption of beta-adrenergic agonists used in sport doping on metal nanoparticles: a detection study based on surface-enhanced Raman scattering.

The adsorption of beta(2)-adrenergic agonist (ßAA) drugs clenbuterol, salbutamol, and terbutaline on metal surfaces has been investigated in this work by means of surface-enhanced Raman scattering (SERS). To assist in this investigation, a previous vibrational (IR and normal Raman) characterization of these drugs was performed, supported by ab initio density functional theory calculations. The application of SERS was aimed to apply this highly sensitive technique, based on localized surface plasmon resonance, in the detection of ßAA at trace concentrations and as a possible alternative method which can be postulated in routine antidoping analysis. The adsorption of these drugs was studied in depth at different experimental conditions: on Au and Ag, at different pHs, and with varying adsorbate concentration. Moreover, plasmon resonance spectroscopy was employed to investigate the adsorption of these drugs on the metal nanoparticles as well as their aggregation. It was found that the adsorption of these molecules is more effective on gold nanoparticles and at acidic pH, based on the direct interaction of the aromatic or aliphatic moieties through ionic or coordination bonds with the metal. These drugs followed a Langmuir adsorption model from which the adsorption constant and the limit of detection can be determined.