Fundamentals and Applications of Surface-Enhanced Raman Spectroscopy (SERS)

When a molecule is adsorbed on some metallic nanostructured surfaces such as silver, copper or gold, it can undergo an enormous enhancement of the Raman signal giving rise to the so called Surface-Enhanced Raman Scattering (SERS). The high sensitivity of this effect allows an accurate structural study of adsorbates at very low concentrations. The SERS effect has historically been associated with the substrate roughness on two characteristic length scales. Surface roughness on the 10 to 100 nm length scale supports localized plasmon resonances which are considered as the dominant enhancement mechanism of SERS (Electromagnetic Enhancement Mechanism: SERS-EM). It is usually accepted that these electromagnetic resonances can increase the scattered intensity by an average factor of ca. 104 to 107. A secondary mechanism often thought to require atomic scale roughness is referred to as Charge Transfer (CT) Enhancement Mechanism (SERS-CT). This mechanism involves the photoinduced transfer of an electron from the metal to the adsorbate or vice versa and involves new electronic excited CT states which result from adsorbate–substrate chemical interactions. It is also estimated that such SERS-CT mechanism can enhance the scattering cross-section by a factor of ca. 10 to 102. These two mechanisms can operate simultaneously, depending on the particular systems and experimental conditions, making difficult to recognize each one and to estimate their relative magnitude in a particular spectrum.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Surface-Enhanced Raman spectroscopy of thiobenzoic acid on metal nanoparticles

Molecules adsorbed on some metal surfaces such as silver, copper and gold, can exhibit enormous Surface-enhanced Raman Scattering (SERS). The SERS effect has historically been associated with substrate roughness on two characteristic length scales [1,2]. Surface roughness on the 10 to 100 nm length scale supports the electromagnetic resonances which are the dominant mechanism of enhancement. A second mechanism often thought to require atomic scale roughness, is referred to as the chemical enhancement mechanism. This second mechanism involves the creation of new electronic excited states which result from adsorbate–substrate chemical interactions. These two mechanisms operate simultaneously making it difficult to isolate the role and magnitude of each one. In this work the SERS spectra of thiobenzoic acid (TBA) adsorbed on several silver colloids are recorded by using different excitation wavelengths. Taking advantage of the fact that SERS spectroscopy is both, surface selective and highly sensitive, we have attempted to determine the molecular structure of the surface complex once TBA is adsorbed on the metal. The analysis of the vibrational wavenumbers of the Raman and SERS spectra suggests that this molecule shows unidentate coordination to the silver surface through the sulphur atom. In order to confirm this conclusion DFT calculations have been carried out for different TBA-silver complexes concluding that the unidentate coordination is the most likely interaction of TBA on the metal surface. Wavelength-scanned SERS excitation spectroscopy involves the measurement of SERS signal by using several excitation wavelengths and it was recognized as a useful tool for checking the mechanisms responsible for the SERS enhancement [3]. We have studied the effect of the wavelength within the SERS spectra of TBA on silver colloid prepared by different methods and we have analyzed the intensity of the 8a vibrational mode of TBA recorded at about 1590 cm-1. The intensity of this mode is noticeably higher in the spectrum recorded with the 514.5 nm line (Fig. 1). This result is attributed to the presence of a resonant Raman effect associated to a photoinduced charge-transfer process when using the most energetic excitation line. Finally, it is important to mention the high affinity of TBA for the silver surfaces what allows for a detection limit estimated to be 0.01 microM.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Raman, SERS and DFT study of chemically-adsorbed thiobenzoic acid on silver nanoparticles

Thiocarboxylic acids are organosulphur compounds with general formula RC(O)SH. They are related to carboxylic acids by the replacement of one oxygen by sulphur. Two tautomers are possible, written as RC(S)OH and RC(O)SH. The second one is the majority species in solid state and solution of thiobenzoic acid (TBA) at room temperature [1], but derivatives from both tautomers are known so that the SERS spectrum can be originated by either one. Taking advantage of the fact that SERS spectroscopy is both surface selective and highly sensitive we have attempted to determine the molecular structure of TBA once it is adsorbed on the metal surface. To accomplish this SERS spectra of TBA have been recorded on different silver colloids. A combination of layer-by-layer method with spin-coating deposition of silver nanoparticles have been used to prepare SERS active substrates on which the homogeneity of the SERS signal of TBA has been analyzed. Fig. 1 (I) shows the Raman spectra of TBA in the neat liquid (a), 1 M aqueous solution at pH 14 (b), SERS spectrum of a 5x10-4 M silver colloid prepared by reduction of silver nitrate with sodium borohydride at pH 7 (c) and SERS spectrum of a 5x10-4 M silver colloid prepared by reduction of silver nitrate with hydroxylamine hydrochloride (d). The assignment of the Raman spectra has been based on the present work as well as on previous studies [2-4]. The two bands recorded at 1662 and 2572 cm-1 in Fig.1a, are assigned to (C=O) and (SH) modes, what confirms that the Raman spectrum in the neat liquid is due to the thiolic specie of TBA, RC(O)SH. In the Raman spectrum of the solution (Fig. 1b) a significant redshift of (C=O) mode of 52 cm-1 and the absence of the (SH) band are detected in agreement with the behavior observed in the SERS spectrum (Fig. 1c). The latter confirms that the thiol tautomer of thiobenzoate anion, RC(O)S-, is adsorbed on silver nanoparticles. Other important SERS enhancements have been registered for the following vibrational modes: 8a;ring, (C=O) and (CS) recorded at 1592, 1554 and 928 cm-1 in Fig. 1c and 1d, respectively. The last two modes, (C=O) and (CS), undergo wavenumber shifts of +40 and -40 cm-1 respectively, which are closely related with the coordination of thiobenzoate anion to the metal surface [5]. The analysis of the vibrational wavenumber of these modes suggests that this molecule shows unidentate coordination through the sulphur atom to the metal surface. In order to confirm this fact DFT calculations have been carried out for different silver complexes: I) bridging bidentate ligand, (II) chelating ligand and (III and IV) unidentate ligand (Fig. 2). Theoretical wavenumber of representative bands of these compounds have been compared to the experimental one concluding that the behavior of the unidentate ligand (III) is the most probably coordination type of TBA on the metal surface. In order to confirm these conclusions the SERS spectra of TBA on silver colloid prepared by reduction of silver nitrate with hydroxylamine hydrochloride at different concentration of analyte have been recorded as well (Fig. 1 (II)). It is well known that the SERS enhancement factor depends strongly on different factors and in particular on the adsorption properties of the probe and the analyte concentration on the surface coverage. In this sense TBA has shown a very good detection level for this particular silver colloid it being a highly SERS active molecule. The detection limit is estimated to be 0.01 molar. Finally, Fig. 3 shows a representative Raman mapping of TBA adsorbed on a silver substrate prepared by spin-coating. Generally speaking, the image represents a fairly homogeneous distribution of the SERS intensity highlighting some points where the intensity is stronger as is expected in areas with heterogeneous coverage. The reproducibility of this type of substrate is under study focusing their application as reproducible and ultrasensitive sensing assemblies by using TBA as the target molecule due its good SERS sensitivity.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Highly effective SERS nanopattern substrate. The enhancement is demonstrated using thiophenol as a molecular probe

The number of different types of Surface-enhanced Raman Scattering (SERS) substrates available for experimentation is increasing at high speed. New alternatives are introduced and explored every year in the literature including both novel nano-particles in solution as well as self-assembled or engineered structures with different levels of control over their optical properties. In this work silver nanopattern obtained by the nano-sphere lithography approach was prepared and characterized by AFM. This method basically exploits the regular patterns formed by self-assembly of dielectric (polystyrene, PS) nano-spheres on a surface upon drying. The evaporation of a silver film on top of the array can be followed by the lift-off of the nano-spheres themselves in which case an array of interstitial sites is left on the surface [1-2] (Fig. 1). We have observed in the AFM images that the shape of the nanopatterns is regular but the surface is rough and they are homogeneously distributed with dimensions in the sub-wavelength range.SERS properties of this substrate were examined by using thiophenol (TP) as molecular probe through the preparation of self-assembled monolayer (SAM) by dipping the substrates for 1h in 0.1mM solution of TP in CH2Cl2 at the temperature of 25ºC. Samples were subsequently rinsed with solutions solvents and dried before scanning. The surface interaction of this molecule has been studied by several groups and the most significant Raman change after the adsorption is the disappearance of the S-H stretching mode at about 2566 cm-1 in the SERS spectrum and indicating that an Ag-S bond has been formed [3]. The reproducibility on different areas of this substrate has been analyzed by using this molecular probe concluding that a fairly homogeneous distribution of the SERS intensity is observed (Fig. 2) which is a prerequisite for applications as ultrasensitive sensing assemblies.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Relación entre la distribución de anuros y variables del hábitat en el sector la romelia del parque nacional natural munchique (cauca, colombia)

Se estudió la relación de diferentes parámetros vegetales y variables climáticas con la distribución y la abundancia de la fauna anura en tres tipos de hábitat (bosque maduro, bosque secundario y matorral) entre los meses de abril y septiembre de 2001 en el sector La Romelia del Parque Nacional Natural Munchique, departamento del Cauca, Colombia. Se registró un total de ocho especies de ranas del género Eleutherodactylus, siendo las más abundantes E. capitonis, E. sp. 3 y E. sp. 2, con 73, 57 y 49 individuos, respectivamente. Todas las especies de anuros mostraron preferencia significativa por las hojas como sustrato de percha. En cuanto a la altura o posición vertical, un mayor número de individuos fue observado en las distancias verticales más bajas (I, II, III). Además, la distribución de las ocho especies de ranas no se relacionó con la presencia de fuentes de agua permanente. Los parámetros del hábitat que tuvieron mayor relación con la distribución y abundancia de las ocho especies de anuros fueron la cobertura de las copas en los diferentes estratos, la cobertura de briofitos y bromelias en el suelo, y en ramas y troncos de árboles, arbolitos y arbustos, la densidad de estas formas de crecimiento y la profundidad de la hojarasca

Transferencia y conservación de la infraestructura hidroagrícola en el Alto Río Lerma, Guanajuato

Objetivo - evaluar el estado de conservación de la infraestructura hidroagrícola, como resultado del proceso de transferencia a los usuarios del d.r. 011. Método - análisis estadístico de series de tiempo de las variables de inversión en mantenimiento y conservación, cuotas de riego y volúmenes de agua disponible para riego en el d.r. 011. Resultados - la inversión en conservación y mantenimiento no presenta una tendencia creciente en el período posterior al proceso de transferencia, no obstante que se incrementaron las cuotas de riego pagadas por los usuarios, lo que ha incidido negativamente en el estado físico de las obras. Limitaciones - no hay información disponible suficiente para realizar el análisis estadístico de cada uno de los módulos estudiados. Principales hallazgos - a más de dos décadas de la transferencia del manejo de las obras a los usuarios del d.r. 011, las estructuras de riego presentan un notable deterioro, particularmente los módulos Valle de Santiago y Cortázar, donde gran parte de los canales de distribución de la red menor, se encuentran sin revestir y en malas condiciones

Proteínas de almacenamiento tipo 11S en semillas de olivo (Olea europaea L.). Caracterización mediante técnicas de proteómica

6 páginas, 3 figuras, 1 tabla.-- Trabajo presentado al Simposium Científico–Técnico EXPOLIVA 2007.Los tejidos de reserva de la semilla del olivo acumulan grandes cantidades de proteínas de almacenamiento en forma de cuerpos proteicos. En este trabajo se analizaron extractos proteicos de cotiledón y endospermo mediante electroforesis bidimensional (2-D). Dichas técnicas permitieron detectar el carácter básico de los péptidos p1 y p2, así como el carácter ácido de p3, p4 y p5. La espectrometría de masas de diversos spot aislados, indicó una homología relevante con la subunidad básica de las leguminas de tipo 11S. También se detectó la presencia de diversas isoformas, algunas posiblemente resultantes de modificaciones postranscripcionales. La abundancia de estas proteínas en las semillas maduras de olivo hace que dicho material pueda ser considerado una fuente nitrogenada de posible uso como complemento en nutrición animal. Otras utilidades relevantes podrían explotar un posible carácter discriminatorio entre variedades para el desarrollo de programas de mejora genética en olivo actualmente en curso.Este trabajo fue financiado gracias a los proyectos AGL2003-00719 y MEC BFU2004- 00601/BFI. Los autores agradecen al Consejo Superior de Investigaciones Científicas (CSIC) la concesión de una beca predoctoral (I3P-CSIC 2002).Peer reviewe

La internacionalización del sector hotelero español: evolución y situación actual de las operaciones en el exterior

La industria turística, junto a la industria de la construcción se configuran como los principales motores de la economía española. Además, la primera, puede considerarse como una de las pocas opciones que tiene nuestro país para ser competitivo a nivel mundial. Sirviendo este como argumento de partida, pretendemos mostrar, con el siguiente trabajo descriptivo, la evolución que la industria turística, y más concretamente el sector hotelero, como abanderado de ésta, ha seguido en los últimos años, dónde podrá observarse cuál es la situación actual, y principalmente, el crecimiento tan espectacular que se ha seguido en los últimos años.Turist industry, along with construction industry, are the main driving forces of Spanish economy. Moreover, the former can be regarded as one of the few options our country has in order to compete in the world market. This being our starting point, we try to show by means of a descriptive study, how turist industry has developed. In particular, we pay attention to the hotel sector since it is the main one within turist industry. We provide its evolution, actual situation and the remarkable growth it has experimented in recent years

Differentiated adsorption of thiobenzoic acid and thiobenzamide on silver nanoparticles determined by SERS spectroscopy.

Política de acceso abierto tomada de: https://v2.sherpa.ac.uk/id/publication/15140?template=romeo (Submitted version)Surface-enhanced Raman scattering of thiobenzoic acid and thiobenzamide have been recorded on three different silver colloids in order to find the chemical species responsible for the spectra and to detect differences in the adsorption with respect to their oxygen counterparts, benzoic acid and benzamide, respectively. Very significant and unexpected shifts of opposite sign between the Raman and SERS wavenumbers have been detected. By comparing the experimental and DFT calculated wavenumbers, it can be concluded that the acid is bonded to the metal as thiobenzoate through the sulfur atom with unidentate coordination. SERS spectra of thiobenzamide can be explained by assuming that it is adsorbed as azanion, like in the case of benzamide, linking to the metal through the sulfur and nitrogen atoms of the ionized thiocarboxamide group. In order to support these conclusions, B3LYP/LanL2DZ force field calculations for different complexes of silver cations with the thiobenzoate anion, the neutral thiobenzamide as well as its azanion have been carried out. Additionally, the 8a;nring mode is the most enhanced band in the SERS of both adsorbates pointing to the participation of a metal-to-molecule resonant charge transfer mechanism.Spanish MINECO/FEDER (CTQ2015-65816-R) Junta de Andalucía/FEDER (UMA18-FEDERJA-049 and P18-RT-4592) Ramón Areces Foundatio

Study of the application of PCM to thermal insulation of UUV hulls using Network Simulation Method

The Unmanned Underwater Vehicles (UUV) designed for the detection and neutralization of naval mines are characterized by their high requirements regarding the reduction of the signatures of a vessel (thermal, acoustic, magnetic, etc.), all of them must be reduced in order not to be detected by the mines during the mission. This research work focuses on the reduction of the thermal signature transmitted by the UUV hull, where the use of phase change materials (PCM) is proposed as thermal insulation, placing it between the internal heat source of the UUV and the pressure hull, with the aim of drastically increasing the time in which the external face of the hull of the UUV is within a range of 3 °C and 5 °C temperature increase, allowing it to perform its mission without being detected by the thermal sensors of current naval mines. The simulation will be carried out using the Network Simulation Method for the resolution of the governing equations, which will allow the optimization of the necessary insulation thickness according to the required mission profile. In addition, it is proposed an expression that relates the PCM thickness and the time needed to reach a certain temperature increase