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 × 106. © 2014 the Partner Organisations.This work has been supported by the Spanish Ministerio de Economía y Competitividad (MINECO, grant FIS2010-15405) and Comunidad de Madrid through the MICROSERES II network (grant S2009/TIC-1476), by the Agency of the Ministry of Education of Slovak Republic for the Structural Funds of the European Union, Operational program Education (Doctorand, ITMS code: 26110230013 and KVARK, ITMS code: 26110230084) and Operational program Research and Development (NanoBioSens (ITMS code: 26220220107) and CEVA II (ITMS code: 26220120040)), by the Slovak Research and Development Agency under the contract APVV-0242-11, and by the project CELIM (316310) funded by 7FP EU.Peer Reviewe