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SES 2014, Technische Universität Chemnitz, August 7th - 10th, 2014; organized as a satellite conference of International Conference on Raman Spectroscopy ICORS2014 at Friedrich Schiller University Jena; Conferencia invitada; https://www.tu-chemnitz.de/ses2014/, The strong intensification of the electromagnetic (EM) field near the surface of metal nanoparticles (NPs) with plasmonic properties results in a substantial enhancement of the effective Raman cross-section leading to SERS (Surface-Enhanced Raman Scattering) effect. An interesting strategy for increasing the sensitivity of metal plasmonic NPs is their assembly by means of bifunctional molecules leading to the formation of interparticle junctions (nanogaps), where a large intensification occurs leading to the creation of hot spots. The performance of these systems could improve by providing these hot spots with a specific molecular functionalization, resulting in a large increase of selectivity. Actually, the formation of hot spots in gaps can be simultaneously induced by the molecular functionalization (Figure 1). In this work we present the results obtained by using aliphatic dithiols to induce the NPs linking and the subsequent formation of nanogaps. These molecules have two different roles: a) NPs linking to create hot spots; and b) the molecular hosting inside the interparticle gaps aimed to detect compounds of interest inside such cavities (Figure 1). Additionally, the SERS spectra were able to provide a rich information about some important aspects regarding the adsorption, coordination and structural changes of the linker on the metal. The structural study conducted in this work also permitted the study of the conformational order and packing of the aliphatic chains of these molecules on the metal nanoparticles surface. Finally these platforms were employed in the selective and sensitive detection of chlorinated pesticides which can be inserted in the multilayers of dithiols formed between NPs in hot spots.

Espectroscopia, Universidad de la Rioja, Logroño, La Rioja, 9-11 de julio de 2014; http://www.unirioja.es/espectroscopia2014/, Linear ¿,¿-dithiols with aliphatic nature have been used in this work as linkers to control the aggregation of silver nanoparticles and to induce the formation of interparticle gaps. The interest of these gaps resides in the well-known fact that when plasmonic surfaces are within a close distance, their plasmon modes couple. This event affects the electromagnetic field distribution in a manner that a drastic enhancement occurs in the gaps leading to the creation of hot spots. As a result, the optical response of substances situated inside the hot spots is strongly increased, which is highly valuable for their use in surface-enhanced spectroscopies. In this work we present a study of the formation and the characterization of the gaps formed by using dithiols of different lengths, where both thiol groups are connected by a linear aliphatic chain with 6, 8 and 10 CH2 groups. This characterization was done by using plasmon resonance and transmission electron microscopy (TEM). The Surface-Enhanced Raman Scattering (SERS) technique was employed in the investigation of the adsorption of these dithiols on the metal surface by analysing key structural spectral markers of the adsorption, metal coordination, orientation, ordering and interfacial packing of these molecules on surfaces of silver and gold NPs. The fingerprint character of SERS spectra, the propension rules of SERS and the high sensitivity of this technique make this study possible even at the very low concentration of dithiols sufficient to induce the NPs linking. Dithiol-linked nanoparticles were employed as sensors in the detection of the pesticides aldrin, dieldrin, endosulfan and linden at very low concentrations, taking advantage of the high affinity of these pollutants for aliphatic-like membranes. The sensing ability of these substrates was optimized by varying the surface coverage of dithiols.

Meeting of Nanoscience and Nanotechnology (N&N) in Spain, Madrid, March 11-14 (2014) ; http://www.nanospainconf.org/2014/index.php?conf=14, Spanish Ministerio de Economía y Competitividad (MINECO, Grant FIS2010-15405) and Comunidad de Madrid through the MICROSERES II network (Grant S2009/TIC-1476)

Espectroscoía, Universidad de la Rioja, Logroño, La Rioja, 9-11 de julio de 2014. PO83; http://www.unirioja.es/espectroscopia2014/, ABTS [2,2¿-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)] has been extensively employed to evaluate the free radical trapping capacity of pure compounds and complex mixtures such as biological fluids or foods [1], when it is incubated in presence of a free radical source in the so-called Trolox equivalent antioxidant capacity (TEAC) assay. The latter assay is performed by using a colorimetric experiment, where ABTS is previously oxidized by persulfate to get the radical cation ABTS*+ [2], giving rise to an intense absorbance at 734 nm. In this work we report the formation of the radical cation in the presence of star-shaped silver nanoparticles (AgNS) [3]. ABTS*+ was characterized by surface-enhanced Raman scattering (SERS) and detected at trace concentrations (2 µM). The ABTS*+/AgNS system is proposed here as a reliable substrate to test the antioxidant activity of foods based on the high sensitivity of plasmonic nanostars as an alternative method to the TEAC test

The vibrational characterization of the dye used for detection of amyloid aggregates Thioflavin T (ThT) was carried out by means of Raman and surface-enhanced Raman scattering (SERS). The Raman spectrum of ThT in aqueous solution correlates very well with the spectrum of ThT with the torsional angle between the benzothiazole (BT) and dimethylaminobenzene (DMB) moieties of 37¿ calculated using DFT calculations at the B3LYP/6-31+G** level. The SERS technique was very useful for the detection of two structures of ThT molecules in the vicinity of the metal nanoparticles: directly adsorbed onto the metal surface and molecules forming multilayers. The structure of ThT molecules in multilayers is similar to the structure of free ThT in aqueous solution. The molecules directly adsorbed on the metal surface actually correspond to the molecules with 90¿ torsional angle between the BT and DMB rings.