ANNUAL REPORT 2011 - Instituto de Estructura de la Materia

Apart from the center for accelerators, it is also under construction the instrument WISH (second target station ofISIS facility) in which we are involved in several of its components as well as the development of an update forPEARL (first target station ISIS facility) an instrument specialized in sample environments at extreme pressures.PREPARATION OF METAL NANOPARTICLESThe preparation of metal nanoparticles (NPs) with plasmonic properties has been a priority line of the group duringthis period. We have devoted special attention to the NPs with morphologies that lead to high electromagnetic fieldenhancements. To accomplish this, it has been established experimental conditions that lead up to this kind ofmorphologies. The strategy followed to prepare these systems was: a) Fabrication of NPs giving rise to highelectromagnetic field intensities, like triangular nanoprisms and nanostars; and b) the association of spherical NPsby using bifunctional molecules that lead to the formation of highly effective interparticle cavities or hot spots,where the Raman scattering is markedly enhanced. Different preparation protocols were assayed in order to improvethose already described in the literature. To carry out this task bifunctional molecules as diamines, dithiols, aliphaticdicarboxylates and aromatic dithiols have been used. The characterization of all these systems was carried out bymeans of Plasmon resonance, TEM, SERS and SEF.In this line, we have proceeded to the fabrication of mixed metal systems core/shell, which combines the plasmonicproperties of both metals, preserving the characteristics of the metal surface to the outer layer. For instance we havesuccessfully manufactured Ag/Au and Pt/Au systems by reduction of Ag and Pt on Au nanoparticles, respectively.These systems are characterized by plasmon resonance, microscopy (TEM, SEM and AFM), and SERS. The use ofmolecular markers or sensor systems, which are adsorbed through a different mechanism on the different metal outerlayer, has yielded valuable information about the distribution of metals in the resulting particles and determine theireffectiveness in SERS.Also, within this line, we have carried out the nanofabrication of core/shell systems consisting in magneticnanoparticles coated with Ag and Au, thus resulting systems where the metal plasmonic properties used to cover(shell) are combined with the magnetite magnetic properties of the core. These systems have been characterized byspectroscopic techniques like UV-visible absorption, IR and Raman microscopy, TEM, X-ray diffraction andmagnetization measurements.SURFACE FUNCTIONALIZATION: NANOSENSORSAs in previous years, an important part of the work done in our group during 2010 was devoted to thefunctionalization of metal surfaces obtained by self-assembly of organic molecules. The functionalization cansignificantly increase the sensitivity and selectivity of the nanostructures formed, thus obtaining the highperformancesurfaces by combining the physical properties of the metal substrate with the chemical properties oforganic molecules self-assembled on them. Additionally, these molecules may lead to a biocompatibility of theseNPs, what is in turn advantageous for different medical applications, and to govern the self-assembly of these NPs.Functionalization with host or receptor molecules such as calixarenes and cyclodextrins has been possible thanks tothe inclusion in these moleculesof chemical groups displaying a high affinity for metal surfaces such as the groupdithiocarbamate (DTC). The DTC group has a high affinity for Au and Ag, which has enhanced the efficiency of thefunctionalization, resulting in metal systems/assembler with high performance in detecting contaminants, for illicitdrugs and doping in sport. The detection of these analytes is possible by the existence of hydrophobic cavities inthese hosts, in which the molecules to be detected can be accommodated. Recently, we have started to use other kindof inclusion hosts: the cucurbiturils, applied in the detection of pesticides.Another group of molecules previously used in the functionalization of metal surfaces, the viologens, whose activityis related to their host properties as electron acceptor, were used in the detection of contaminants such polycyclicaromatic hydrocarbons, which act as electron donors. The viologen interact strongly with the metal through ion-pairor charge transfer complexes between viologen and previously attached to the metal halide. During this periodlucigenin was applied in multivariate detection. The huge selectivity of lucigenin and the SERS spectra may lead toa univocal identification in mixtures of pollutants. In particular, this was assayed in mixtures of polycyclic aromatichydrocarbons. The bifunctional viologen dramatically improves the performance of these substances to act ascreators of interparticle spaces with high electromagnetic field enhancement (hot spots), and also by acting ascontact assemblers. This work was made in the frame of an Associated Unit with the University of Malaga.Finally we have studied the functionalization molecules using bifunctional molecules with aliphatic character(diamines, dithiols and aliphatic dicarboxylate), as well as with aromatic character (phenilene dithiols anddiisocyanides). The last compounds are also able to induce the formation of hot spots by NP-NP associations, withhigh performances in the detection and catalysis of substrates localizaed inside these cavities. All these works were61