Materials science has observed a continuous increase in the use of metal nanoparticles in a wide range of studies, from fundamental physics to technological applications such as photocatalysis and optical communication devices. This broad scope has the same fundamental origin, the localized surface plasmons, whose excitation leads to strong light confinement, especially in the vicinity of closely spaced nanoparticles, the hot spots. The field amplification may be used to amplify the Raman scattering of adsorbed molecules, which is known as surface-enhanced Raman scattering (SERS). A crucial and limiting characteristic of SERS hot spots is their very localized nature, that influences the SERS intensity reproducibility as well as the probabilities of observation of single-molecule SERS signals. In this paper we discuss the correlation between SERS performance and gold nanorod cluster structures using transmission electron microscopy, SERS spectra and numerical simulations. The experimental data showed interesting behavior for the combination of end-to-end and side-by-side interactions, revealing the possibility of creating strong hot spots with a more extended spatial distribution. The results give insights into the development of high-performance SERS substrates.

A complete procedure including synthesizing gold nanoparticles and further hotspots stabilization is presented. Colloidal gold synthesis followed a citrate reducing reaction, then, an ideal condition for SERS enhancement with quantitative purposes was reached by searching equilibrium between salt- and analyte-induced aggregation. Under this condition, a mild aggregation is produced, along with "free sites" available on the metal surface where analyte could easily interact. As a consequence, suitable linear concentration intervals and high quality SERS spectra were obtained allowing building multivariate quantitative models. For adenine as probe molecule, LOD values were around 10-8 mol L-1, even at low laser power and short exposure time during spectral acquisition. The hotspot stabilization procedure, as shown here, allows dealing with samples or highly complex analytical matrices that can easily cause undesirable agglomerate formation like those from biological origin.

Nanocompósitos à base de amido de mandioca, argila sintética hectorita e açúcar invertido (plastificante) foram preparados por processo em meio aquoso (casting) produzindo filmes transparentes e homogêneos. Pequenas quantidades de argila (5-15% em massa) produzem principalmente nanocompósitos esfoliados, enquanto grandes quantidades (30% em massa) promovem a formação de nanocompósitos intercalados. Os espectros FT-Raman mostram que bandas sensíveis à ligação de hidrogênio em grânulos de amido são progressivamente deslocadas para frequências menores quando o teor de argila é aumentado. Os nanocompósitos mostram um comportamento térmico semelhante até 320 ºC, enquanto a decomposição da biomolécula em cerca de 500 ºC é dependente do teor de argila. A liberação de CO2 em aproximadamente 300 ºC (decomposição não oxidativa das cadeias poliméricas) diminui se comparada com o desprendimento desse gás em 500 ºC quando a quantidade de argila é aumentada. Filmes com teor de argila maior que 10% não mostram melhora substancial nas propriedades de alongamento ou resistência.

Polymer-clay nanocomposites (PCN) based on cassava starch, synthetic hectorite clay and inverted sugar cane syrup (plasticizer) were prepared by solvent-assisted (casting) process producing transparent and homogeneous films. Small amounts of clay (5-15 wt.%) resulted mainly in exfoliated nanocomposites while large amounts (30 wt.%) promote the intercalated nanocomposites formation. FT-Raman bands sensitive to hydrogen bonding in starch granules are progressively shifted to lower wavenumbers as the clay content is raised. Nanocomposites show a similar thermal behavior up to 320 ºC while the biomolecule decomposition at about 500 ºC is dependent on the clay content. CO2 release at about 300 ºC (non-oxidative decomposition of polymeric chains) decreases if compared to the gas delivery at ca. 500 ºC, as the clay content is increased. Films with clay content higher than 10 wt.% show no substantial benefit for either elongation or resistance properties.

This work reports on the SERS activity of a nanostructured substrate that was obtained by electrodepositing gold over a template consisting of polystyrene microspheres. This substrate displayed superior SERS performance for the detection of 4-merctaptopyridine as compared to a conventional roughened Au electrode. In order to investigate the substrate capability for the detection at low concentration limits, a series of Rhodamine 6G (1 nM) spectra were registered. Our spectral dynamics data is in agreement with single-molecule behavior, showing that the control over the substrate morphology is crucial to enable the production of highly reproducible and sensitive SERS substrates.

Complexos do tipo trans-[Ru(L)(NH3)4(L’)](PF6)n, onde L = 4-cianopiridina (CNpy), NCS-, CN-, e L’ = CNpy, 1,4-ditiano (1,4-dt), 4-mercaptopiridina (pyS) e tionicotinamida (tna), foram sintetizados e caracterizados. SAMs sobre ouro formadas com os complexos que contêm ligantes sulfurados foram estudadas por desorção redutiva e espectroscopia SERS. Dependendo da natureza do ligante L’, a capacidade retiradora do ligante CNpy mostrou ser forte o suficiente para oxidar parcialmente o átomo de rutênio e, em consequência, deslocalizar densidade eletrônica s do ligante localizado em posição trans. Os resultados de desorção redutiva mostraram que a estabilidade das SAMs formadas está diretamente relacionada a este efeito.

Trans-[Ru(L)(NH3)4(L’)](PF6)n type complexes, where L = 4-cyanopyridine (CNpy), NCS-, CN-, and L’ = CNpy, 1,4-dithiane (1,4-dt), 4-mercaptopyridine (pyS) and thionicotinamide (tna), were synthesized and characterized. SAMs on gold of the complexes containing sulfur were studied by reductive desorption and SERS spectroscopy. Depending on the nature of L’, the withdrawing capability of the CNpy ligand is strong enough to partially oxidize the ruthenium atom and, as a consequence, delocalize the s electronic density from the trans located ligand. The reductive desorption results showed that the stability of the SAMs is directly related to this effect.

This paper reports the use of Raman and infrared techniques for the qualitative and quantitative analysis of plasticizers in polyvinylchloride (PVC) commercial films. FT-Raman marker bands were indentified for di-2-ethyl-hexyl adipate (DEHA) and di-2-ethyl-hexyl phthalate (DEHP), allowing for the rapid identification of these species in the commercial film. Quantitative analysis by FT-IR resulted in plasticizers concentrations ranging from 11 to 27% (w/w). Considering the little sample preparation and the low cost of the techniques, FT-IR and FT-Raman are viable techniques for a first assessment of plasticizers in commercial samples.

O processo redox da metaloproteína cyt c foi observado através da utilização de eletrodos de ouro modificados com os complexos [Ru(CNPy)(NH3)4(1,4-dt)]2+ e [Ru(CNPy)(NH3)4(pyS)]2+ , onde CNPy = 4-cianopiridina, pyS = 4-mercaptopiridina e 1,4-dt = ditiano. Os valores dos potenciais redox observados indicam a forma in natura da proteína. A forma dos voltamogramas, todavia, é dependente da conformação do complexo modificador sobre a superfície que, por sua vez, foi determinada por SERS. Os potenciais de dessorção redutiva, observados em -0,52 e -0,64 V vs Ag|AgCl|Cl- para os complexos [Ru(CNPy)(NH3)4(1,4-dt)]2+ e [Ru(CNPy)(NH3)4(pyS)]2+ , respectivamente, são indicativos do tipo de ligação com a superfície e da capacidade pi retiradora do ligante CNpy.

The redox process of the cyt c metalloprotein was assessed by the cationic SAMs formed with [Ru(CNPy)(NH3)4(1,4-dt)]2+ and [Ru(CNPy)(NH3)4(pyS)]2+ complexes on gold, where CNPy = 4-cyanopyridine, pyS = 4-mercaptopyridine and 1,4-dt = dithiane. The observed cyt c redox potentials are indicative of the native protein form. The voltammograms, however, were observed to be affected by the conformation of the modifiers, determined by SERS spectroscopy. The [Ru(CNPy)(NH3)4(pyS)]2+ complex, which exhibits trans conformation on the surface, presented a well-defined voltammogram. On the other hand, the gauche conformation of the [Ru(CNPy)(NH3)4(1,4-dt)]2+ SAM seems to make the assessment of the cyt c hET reaction difficult. The reductive desorption potentials, at -0.52 and -0.64 V vs Ag|AgCl|Cl- for the [Ru(CNPy)(NH3)4(1,4-dt)]2+ and [Ru(CNPy)(NH3)4(pyS)]2+ SAMs, respectively, are indicative of the bonding mode with the surface and the pi withdrawing capability of the CNpy ligand.

Surface-Enhanced Raman Scattering - SERS - underwent huge advances since a single-molecule Raman spectrum was obtained in 1997. New theoretical and experimental approaches emerged since then leading to a better understanding of the enhancement mechanisms and to a significant improvement in the Raman signal. This review presents the current status of the SERS effect and the promising ways of designing and preparing high performance SERS-active substrates.

The potentialities of X-ray Absorption Near Edge Spectroscopy (XANES) of the N K edge (N K) obtained with the spherical grating monochromator beam line at the Brazilian National Synchrotron Light Laboratory are explored in the investigation of poly(aniline), nanocomposites and dyes. Through the analysis of N K XANES spectra of conducting polymers and many other dye compounds that are dominated by 1s<FONT FACE=Symbol>®p</FONT>* transitions, it was possible to correlate the band energy value with the nitrogen oxidation states. An extensive N K XANES spectral database was obtained, thus permitting the elucidation of the nature of different nitrogens present in the intercalated conducting polymers.

Os processos redox da polianilina dopada secundariamente e dopada primariamente pré-aquecidas (150oC, 6-12 horas) foram investigados pela espectroscopia Raman ressonante in-situ. Os espectros Raman do polímero dopado secundariamente mostram uma maior dependência com o aumento do potencial do que o polímero dopado primariamente pré-aquecido. Estes diferentes comportamentos foram atribuídos à presença de diferentes graus de ligações cruzadas nos polímeros. A presença de diferentes quantidades de ligações cruzadas foi confirmada por análise termogravimétrica, espectroscopia UV-vis e voltametria cíclica.

The redox processes of secondarily doped and the pre-heated primarily doped polyaniline (150oC, 6-12 h) were investigated by in-situ resonance Raman spectroscopy. Raman spectra of secondarily doped polymer is more dependent on potential than those observed in the pre-heated primarily doped polymer. These different behaviors were attributed to the presence of different degree of crosslinking in the polymers. The presence of different amounts of crosslinking was confirmed by thermogravimetric analysis, UV-vis spectroscopy and cyclic voltammetry.

The Surface Enhanced Raman Scattering (SERS) effect was observed for the first time in 1974, but it was only considered a new effect three years later, hence, nearly twenty years ago. Since its discovery, a significant amount of investigations have been performed aiming at to clarify the nature of the observed enhancement, to improve the surface stability and to establish applications which nowadays range from the study of biomolecules to catalysis. Some of the more relevant aspects of this effect which have been examined across the last two decades are summarized in this paper which presents the introductory aspects of SERS alongside with several of its applications.