ANNUAL REPORT 2011 - Instituto de Estructura de la Materia

done in collaboration with researchers of the University P. J. Safarik of Kosice (Slovak Republic) and withresearchers of the University of Hokkaido from Sapporo (Japan).INTERACTION BETWEEN METAL NANOPARTICLES AND BIOMOLECULESMethods for the functionalization of NPs with biomolecules to confer greater biocompatibility were also testedduring the last year. In this sense, we conducted a study of the adsorption of peptides of varying sequence anddifferent polarity and hydrophobicity to evaluate their affinity for metal surfaces. In particular, our attention wasfocused on studying the adsorption of cysteine and cystine, two amino acids with thiol groups and disulfide bonds,whose stability has been studied in the presence of Ag and Au. This work was carried out in collaboration withresearchers from the University of Paris XIII.Related to the latter research we have also conducted the study of the adsorption on metals of high biologicalsignificance proteins such as human and bovine albumin and myoglobin, an important protein related to the oxygentransport and storage in muscles. Methods have been tried to increase the affinity of peptides and proteins by metalsurfaces employed in SERS, namely we have accomplished the functionalization of NPs with polysaccharidecompounds having a high affinity for metals, such as chitosan and alginate. This work has been done incollaboration with researchers from the University of Chile and the University of Florence.The last year, we continued the research dealing with the structural analysis of biological materials difficult tocharacterize by conventional spectroscopic techniques. In this area we have carried out a study of the adsorption onmetallic NPs of humic substances and melanins, which result from the digestion processes induced by fungi. Inparticular, we have conducted a SERS / SEF study on humic substances of different origins (soil, leonardite, lignite)on both Ag NPs as on metal electrodes, in order to study the effect of the applied potential on the SERS spectra andSEF of these substances. Finally, we developed a study of the structure of the organic matter and charcoal extractedfrom forest lands that have suffered a fire, by using Ag NPs. These studies were performed in collaboration withresearchers from the Universities of Bologna and Florence.We have re-initialized a researching line based on the application of metal NPs in the characterization ofanthraquinonic natural substances with potential antitumor properties. In particular, this study has focused onparietin, a pigment present in lichens of Xanthoria parietina genre. In addition, we have also conducted a study ofthe distribution of pigment in the leaves of these lichens by Raman imaging. This work was done in collaborationwith the Department of Biophysics of the University PJ Safarik in Kosice (Slovak Republic),Recently, we have started a new line of work also in collaboration with Department of Biophysics, University PJSafarik in Kosice and the Institute of Experimental Physics, Slovak Academy of Sciences, consisting of the study bySERS and SEF of thioflavin dye SEF and its interaction with amyloid peptides. The interest of this research resideson the fact that the latter compounds are considered precursors of the Alzheimer's disease. This study aims atcharacterizing the changes in the structure of the dye in the complex with amyloids, in order to carry out thedetection of small quantities of the dye, which may allow the detection of low amounts of amyloid compound,leading to an early detection of the disease.SURFACE-ENHANCED FLUORESCENCE ON METAL SURFACES (SEF)During this past year we have continued with the technical implementation of the SEF (Surface-enhancedFluorescence) on NPs in colloidal suspension. This method has allowed the study of adsorption and aggregation ofdrugs, especially antitumor drug emodin, and anti-inflammatory drug piroxicam on metal nanoparticles. It has alsobeen found that the functionalization of metal nanopatículas SEF is crucial, since the intensification of fluorescencerequires a certain distance of the fluorophore on the metal. The interaction of these drugs with albumin results in aconsequent increase in the SEF spectra, along with the SERS spectra, circular dichroism spectra and fluorescencelifetime have led to important results on the structural changes undergone by these systems once adsorbed on themetal surface. In particular, we have studied thefluorescence quenching that the drugundergoesin the complexwithalbumin andin the presence ofAgNPs, and the different contributions to this quenching from the so-calledstaticand dynamic quenching mechanisms.Besides, as a part of MICROSERS project supported by Comunidad de Madrid, a new collaboration with UAM hasbeen established in order to design new systems for controlled release of drugs. These systems are based on poroussilicon. The preliminary results obtained have been satisfactories since we could detect the antitumoral agent emodinby SEF using this method of infiltration.This line ofinvestigation is being conductedby Prof.Mª PazSevilla.62