Aplicaciones de la espectroscopía SERS (Surface-Enhanced Raman Scattering) a la detección de pigmentos orgánicos naturales en objetos del Patrimonio Cultural

16 páginas, 17 figuras.La espectroscopía Raman, cuyas prestaciones se han visto considerablemente mejoradas en los últimos 15 años debido a la introducción de técnicas de microscopía (que han sido posibles gracias a importantes avances tecnológicos en filtros ópticos y detectores de alta sensibilidad), se ha convertido en una técnica de identificación molecular de gran utilidad en el campo del Patrimonio Cultural [1]. Al igual que la más conocida espectroscopía Infrarroja, la espectroscopía Raman proporciona información sobre los compuestos moleculares presentes en la muestra bajo estudio, ampliando por ello la información acerca de la presencia de elementos químicos que suministran otras técnicas espectroscópicas tales como XRF, SEM - EDX, PIXE y LIBS utilizadas habitualmente en el análisis de objetos artísticos [2]. Hoy en día podemos encontrar la técnica de microscopía Raman en los departamentos de Conservación y Restauración de los más importantes Museos y Bibliotecas de todo el mundo, utilizándose como técnica no destructiva (incluso in situ) para diagnóstico de diferentes materiales que van desde los pigmentos inorgánicos hasta los biomateriales, en objetos artísticos tan diferentes como manuscritos, pinturas, textiles, cerámicas, vidrios, esculturas, monumentos, e incluso momias o cañones hundidos. La información que se obtiene puede resultar decisiva para la datación y autenticación de las obras artísticas, y ayuda a determinar los cambios físicos y/o químicos que han contribuido a su deterioro a través de la identificación de los productos de degradación de los materiales originales.Agradecemos al MICINN (Proyectos FIS2007-63065 y CONSOLIDER CSD 2007- 0058) y a la Comunidad de Madrid (MICROSERES, S2009TIC-1476) por la financiación parcial de los trabajos aquí expuestos. Agradecemos también el apoyo recibido de la Red Temática de Patrimonio Histórico y Cultural (CSIC). MVC y EdP agradecen al CSIC y al FSE 2007-2013 la concesión de sus respectivos Contratos post- y predoctoral.Peer reviewe

Superficies metálicas nanoestructuradas y su funcionalización para sensores moleculares basados en espectroscopía vibracional (Raman e infrarroja ) intensificada por superficies

15 páginas, 7 figuras.-- En prensa.-- El pdf esta en formato pre-print.Las nanoestructuras metálicas presentan propiedades ópticas singulares debido a los plasmones superficiales localizados (Localized Surface Plasmons) que soportan. La excitación resonante de los mismos produce enormes intensificaciones del campo electromagnético local en las proximidades de las nanoestructuras metálicas, efecto que puede aprovecharse para aumentar la sensibilidad de las técnicas de espectroscopía vibracional (dispersión Raman y absorción infrarroja) que son idóneas para llevar a cabo la caracterización requerida en un sensor molecular. Cuando las moléculas a detectar no presentan afinidad por los sustratos metálicos, se hace necesario funcionalizarlos adecuadamente para conseguir que esas moléculas se aproximen lo suficiente a las nanoestructuras metálicas como para que se beneficien de los enormes campos electromagnéticos locales y, por lo tanto, puedan ser detectadas mediante las técnicas de espectroscopía vibracional intensificadas SERS (Surface-enhanced Raman Scattering)y/o SEIRA (Surface-enhanced Infrared Absorption). Se presentan ejemplos de detección con esta técnicas de cantidades traza de moléculas de interés biológico y/ o medioambiental, utilizando sustratos metálicos nanoestructurados preparados por diferentes métodos.Los autores agradecen la financiación recibida del Ministerio de Educación y Ciencia de España (Proyectos FIS2004-00108 y FIS2007-63065) y de la Comunidad de Madrid (Proyecto MICROSERES, S-0505/TIC-0191). L.G. agradece la beca I3P concedida por el CSIC y Z.J. agradece al “VI Programa Marco” de la Unión Europea la “Marie Curie Early Stage Research Training Fellowship” concedida dentro del Contrato MEST-CT-2004-513915.Peer reviewe

Silver nanoparticles active as surface-enhanced Raman scattering substrates prepared by high energy irradiation

In surface-enhanced Raman scattering (SERS) technique the preparation of metal substrates containing minimum hindrance from impurities is an important issue. The synthesis of silver nanoparticles (Ag NPs) active as SERS substrates and having the above-mentioned advantage, were obtained by electron beam irradiation of Ag+ aqueous solutions. Ag+ ions were reduced by free radicals radiolytically generated in solution without the addition of chemical reductants or stabilizing agents. The metal colloids were characterised by UV–Vis spectroscopy and scanning electron microscopy, monitoring the nanoparticles’ growth process that depends on the irradiation dose and the initial AgNO3 concentration. Nanoparticles of long-time stability and with different size and shape, included silver nanocubes, were synthesised by varying the irradiation dose. Different tests on the SERS activity of Ag NPs obtained by electron beam irradiation were performed by using benzenethiol as a probing molecule, achieving a good magnification of the adsorbate Raman bands.Authors acknowledge Ministerio de Educación y Ciencia project number FIS2007-63065 and Comunidad Autónoma de Madrid project number S-0505/TIC/0191 MICROSERES for financial support. The authors also acknowledge Dr. J. D. Gomez Varga for the ESEM measurements at the Institute of Polymer Science and Technology (CSIC).Peer Reviewe

In situ detection of flavonoids in weld-dyed wool and silk textiles by surface-enhanced Raman scattering

4 pages, 3 figures.Luteolin and apigenin flavonoid have been detected in silk and wool fibres dyed with weld (Reseda luteola L.) through surface-enhanced Raman scattering (SERS) measurements carried out on the fibre. For such purpose, Ag nanoparticles were produced and immobilised in situ via the laser photoreduction of a silver nitrate water solution in contact with the fibre. Control SERS spectra of pure luteolin and apigenin, as well as of mixtures of them, on analogous Ag nanoparticles were also obtained. In this work flavonoids with a similar molecular structure were identified on dyed fibres for the first time without previously hydrolysing the mordant-dye complex.This work has been partially supported by the Ministerio de Educación y Ciencia of Spain (Projects FIS2004-00108 and FIS2007-63065) and Comunidad de Madrid (S-0505/TIC/0191 MICROSERES). Z.J. acknowledges the European Community’s Sixth Framework Programme for Marie Curie Early Stage Research Training Fellowship (Contract MEST-CT-2004-513915). The Red Temática del Patrimonio Histórico (CSIC) is also acknowledged. Eu-ARTECH project (FP6-RII3-CT-2004-506171) is acknowledged for the reference textile samples.Peer reviewe

Effect of pH on the chemical modification of quercetin and structurally related flavonoids characterized by optical (UV-visible and Raman) spectroscopy

In this work we report the study of the chemical modifications undergone by flavonoids, especially by quercetin (QUC), under alkaline conditions by UV-visible absorption, Raman and surface-enhanced Raman scattering (SERS) spectroscopy, the study was performed in aqueous solution and also on Ag nanoparticles (AgNPs). Several processes are involved in the effect of alkaline pH both in solution and on AgNPs: autoxidation affecting mainly the C-ring of the molecule and giving rise to the molecular fragmentation leading to simpler molecular products, and/or the dimerization and further polymerization leading to species with a higher molecular weight. In addition, there exists a clear structure-instability correlation concerning mainly particular groups in the molecule: the C3-OH group in the C-ring, the catechol moiety in the B-ring and the C2C3 bond also existing in the C-ring. QUC possesses all these groups and exhibits high instability in alkaline solution. The SERS spectra registered at different pH revealed a change in the dimerization protocol of QUC going from the A- and C-rings-like-condensation to B-ring-like-condensation. Increasing the knowledge of the chemical properties of these compounds and determining the structure-activity relationship under specific environmental factors allow us to improve their beneficial properties for health as well as the preservation of Cultural Heritage objects, for example, by preventing their degradation. This journal is © the Partner Organisations 2014.This work was financially supported by MINECO (Projects FIS2010-15405, and CONSOLIDER CSD2007-0058/TCP) and the Comunidad de Madrid (MICROSERES II Project S2009/ TIC1476). This work was also supported by the Agency of the Ministry of Education of Slovak Republic for the Structural funds of the European Union, Operational program Research and Development (Contract: NanoBioSens, ITMS code: 26220220107) and the EU 7FP project CELIM 316310.Peer Reviewe

Adsorption and catalysis of flavonoid quercetin on different plasmonic metal nanoparticles monitored by SERS

Raman and surface-enhanced Raman scattering spectroscopy were used to follow the chemical modification of quercetin (QUC) on silver nanoparticles. Different metallic systems were fabricated to check the influence of the interface, in terms of electric charge or total available surface, on the catalytic change undergone by QUC. The effect of QUC surface coverage was crucial to reveal information about the different orientation and the interaction mechanism with the metal at different concentrations of this flavonoid. Surface-enhanced Raman scattering spectra of good quality of QUC were observed at concentrations down to 10-8 M. Chemical modifications in the presence of nanostructure metal surfaces include oxidation followed by a subsequent polymerization via a condensation of rings whereas different chemical species have been recognized under different experimental conditions. The assignment of the new species formed on the metal surface was conducted. Copyright © 2012 John Wiley & Sons, Ltd.Supported by the SpanishMinisterio de Ciencia e Innovación (grant FIS2010-15405) and Comunidad de Madrid through the MICROSERES II network (grant S2009/TIC-1476). Support from the Red Temática del Patrimonio Histórico (CSIC). the European Community’s Sixth Framework Programme for Marie Curie Early Stage Research Training Fellowship (contract number MEST-CT-2004-513915).Peer Reviewe

Structural analysis of the neuropeptide substance P by using vibrational spectroscopy

12 pags., 8 figs., 1 tab.Substance P (SP) is one of the most studied peptide hormones and knowing the relationship between its structure and function may have important therapeutic applications in the treatment of a variety of stress-related illnesses. In order to obtain a deeper insight into its folding, the effects of different factors, such as pH changes, the presence of Ca ions, and the substitution of the Met-NH moiety in the SP structure, was studied by Raman and infrared spectroscopies. SP has a pH-dependent structure. Under acidic–neutral conditions, SP possesses a prevalent β-sheet structure although also other secondary structure elements are present. By increasing pH, a higher orderliness in the SP secondary structure is induced, as well as the formation of strongly bound intermolecular β-strands with a parallel alignment, which favour the self-assembly of SP in β-aggregates. The substitution of the Met-NH moiety with the acidic functional group in the SP sequence, giving rise to a not biologically active SP analogue, results in a more disordered folding, where the predominant contribution comes from a random coil. Conversely, the presence of Ca ions affects slightly but sensitively the folding of the polypeptide chain, by favouring the α-helical content and a different alignment of β-strands; these are structural elements, which may favour the SP biological activity. In addition, the capability of SERS spectroscopy to detect SP in its biologically active form was also tested by using different metal nanoparticles. Thanks to the use of silver NPs prepared by reduction of silver nitrate with hydroxylamine hydrochloride, SP can be detected at very low peptide concentration (~ 90 nM). However, the SERS spectra cannot be obtained under alkaline conditions since both the formation of SP aggregates and the lack of ion pairs do not allow a strong enough interaction of SP with silver NPs. [Figure not available: see fulltext.].This work was supported by the Scientific Grant Agency of the Ministry of the Education of Slovak Republic (APVV-15- 0485) and the Ministerio de Economía y Competitividad from Spain under the grant FIS2017-84314-R

Structural analysis of the neuropeptide substance P by using vibrational spectroscopy

Substance P (SP) is one of the most studied peptide hormones and knowing the relationship between its structure and function may have important therapeutic applications in the treatment of a variety of stress-related illnesses. In order to obtain a deeper insight into its folding, the effects of different factors, such as pH changes, the presence of Ca2+ ions, and the substitution of the Met-NH2 moiety in the SP structure, was studied by Raman and infrared spectroscopies. SP has a pH-dependent structure. Under acidic\u2013neutral conditions, SP possesses a prevalent \u3b2-sheet structure although also other secondary structure elements are present. By increasing pH, a higher orderliness in the SP secondary structure is induced, as well as the formation of strongly bound intermolecular \u3b2-strands with a parallel alignment, which favour the self-assembly of SP in \u3b2-aggregates. The substitution of the Met-NH2 moiety with the acidic functional group in the SP sequence, giving rise to a not biologically active SP analogue, results in a more disordered folding, where the predominant contribution comes from a random coil. Conversely, the presence of Ca2+ ions affects slightly but sensitively the folding of the polypeptide chain, by favouring the \u3b1-helical content and a different alignment of \u3b2-strands; these are structural elements, which may favour the SP biological activity. In addition, the capability of SERS spectroscopy to detect SP in its biologically active form was also tested by using different metal nanoparticles. Thanks to the use of silver NPs prepared by reduction of silver nitrate with hydroxylamine hydrochloride, SP can be detected at very low peptide concentration (~ 90 nM). However, the SERS spectra cannot be obtained under alkaline conditions since both the formation of SP aggregates and the lack of ion pairs do not allow a strong enough interaction of SP with silver NPs. [Figure not available: see fulltext.]