Surface-Enhanced Infrared Absorption SEIRA

Thin film of metal clusters enable other types of surface enhancement, one of these is the surface enhanced infrared absorption (SEIRA) spectroscopy. The enhancement is an addition of electromagnetic field effects and chemical effects, therefore highly dependent on the distance to the cluster layer and on the nano-structure of the cluster layer. In fact most studies done point out that the effect is very short ranged and only applicable to the first monolayer adsorbed to the surface. Compared to standard infrared spectroscopy and Surface enhanced Raman scattering SEIRA has a remarkable signal to noise ratio and the 

An example of a specific application of the technique is the detection of Salmonella sp, whereby antibodies to the organism are bound to the chip surface. After recording the spectrum the chip is incubated in a Salmonella containing solution, binding the Salmonella bacteria to the cluster surface. The second spectrum is recorded and overlaid with the original spectrum. In such an experiment a band shift from the original bands at 1085 and 990 cm to 1045 cm was obtained, which was assigned to a phospholipid in the cell wall of the captured cell, 

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Alternatively, various analytical methods based on SPR phenomenon have been developed, including surface plasmon field-enhanced Raman scattering (SERS) [7], surface plasmon field-enhanced fluorescence spectroscopy (SPFS) [8-11], surface enhanced second harmonic generation (SHG) [12], surface enhanced infrared absorption (SEIRA) [13], surface plasmon field-enhanced diffraction spectroscopy (SPDS) [14-18], Most of these methods take advantage of the greatly enhanced electromagnetic field of surface plasmon waves, in order to excite a chromophoric molecule, e.g., a Raman molecule or a fluorescent dye. Therefore, a better sensitivity is expected. 

Furthermore, it is possible to increase the sensitivity of the IR technique, and thus the probability of detecting transient surface species characterized by (very) low absorption coefficients (such as the intermediate species present during the first steps of the polymerization reaction on the Phillips catalyst) by exploiting the surface-enhanced infrared absorption (SEIRA) effect. It is known that molecules adsorbed on metal island films or particles exhibit 10-1000 times more intense infrared absorption than would be expected from conventional measurements without the metal (253-256). The possibility of performing SEIRA spectroscopy should therefore be expected to provide an opportunity to better investigate the nature of the intermediate species, not only for ethene polymerization on Cr(II)/ Si02, but for other reactions on solid catalysts. 

SIERA Surface-enhanced infrared absorption As in the case of surface-enhanced Raman scattering (SERS), molecules adsorbed on metal island films or particles exhibit intense infrared absorption several folds higher than what one would expect from conventional measurements without the metal. This effect is referred to as surface-enhanced infrared absorption (SEIRA). 

Since the enhancement of IR absorption is one of the important characteristics in abnormal IR effects, it may be interesting to compare the AIREs with the phenomenon of surface-enhanced infrared absorption (SEIRA) reported in the literature. The SEIRA was discovered by Hartstein et al. [96] in the early 1980s and describes the phenomenon of the enhancement of IR absorption for some specific... 

Surface enhanced infrared absorption (SEIRA) has been observed in external reflection spectroscopy [185], for further details, see Sect. 5.2.5. 

The phenomenon of surface-enhanced infrared absorption (SEIRA) spectroscopy involves the intensity enhancement of vibrational bands of adsorbates that usually bond through contain carboxylic acid or thiol groups onto thin nanoparticulate metallic films that have been deposited on an appropriate substrate. SEIRA spectra obey the surface selection rule in the same way as reflection-absorption spectra of thin films on smooth metal substrates. When the metal nanoparticles become in close contact, i.e., start to exceed the percolation limit, the bands in the adsorbate spectra start to assume a dispersive shape. Unlike surface-enhanced Raman scattering, which is usually only observed with silver, gold and, albeit less frequently, copper, SEIRA is observed with most metals, including platinum and even zinc. The mechanism of SEIRA is still being discussed but the enhancement and shape of the bands is best modeled by the Bruggeman representation of effective medium theory with plasmonic mechanism pla dng a relatively minor role. At the end of this report, three applications of SEIRA, namely spectroelectrochemical measurements, the fabrication of sensors, and biochemical applications, are discussed. 

Two of the many enhanced optical phenomena in surface-enhanced spectroscopy are surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA). These two phenomena and now analytical techniques can be described as a new branch of vibrational spectroscopy that deals with the spectra of molecules on specially fabricated nanostructures with the... 

More complicated dependences are observed when two layers are located on the surface of the ATR element. The optical properties of a hemicylin-drical IRE-thin (d < 50 nm) metal hhn-hlm system, called the Kretschmann configuration [84] (Fig. 2.36a), were actively investigated in the seventies and eighties (see, e.g.. Ref. [85]) regarding the possibility of SEW excitation at the metal-outer layer interface. However, even without exploiting this and surface-enhanced infrared absorption (SEIRA) (Section 3.9.4) effects, optical enhancement may be achieved in the ATR spectrum of a layer deposited on metal. Because of this, the Kretschmann configuration has found wide application in the investigation of nanolayers located on the metal surfaces, especially at the metal-solution interface (Section 4.6.3). 

The surface enhanced infrared absorption (SEIRA) effect, which is closely related to the better known surface enhanced Raman (SERS) effect, was... 

Vibrational absorption [14, 15]. Molecules adsorbed on metal nanoparticles show an infrared light absorption (due to vibrational transitions) which is amplified of a factor 10 -10 compared to the molecule without the metal. This phenomenon is called surface-enhanced infrared absorption (SEIRA). 

Infrared ER spectrometry has no mechanism of intensity enhancement, in contrast to other methods such as RA spectrometry to be described in Chapter 10 and surface-enhanced infrared absorption (SEIRA), mentioned in Chapter 13. Nonetheless, infrared ER spectrometry provides a unique technique for utilizing s- and p-polarized radiations for obtaining information governed by the surface selection rule on the transition dipoles of molecular vibrations. Theoretical analysis of the information obtained by this technique has the possibility for elucidating molecular orientations in thin films on dielectric substrates and molecular interactions in a wide variety of materials, including liquid crystals. 

Many other applications and developments of the ATR method and accessories have been undertaken, including devising special apparatus for specific purposes. Monitoring chemical reactions in solution is an important application of the ATR method, and a variety of studies have been reported. An important example in this field of research is a combination of the ATR method with the surface-enhanced infrared absorption (SEIRA) [5] technique SEIRA is a phenomenon by which the intensities of the infrared absorption bands of a chemical species adsorbed onto the surface of a thin metal layer consisting of very small metal particles are enhanced. When the ATR method is used for measuring SEIRA,... 

Interaction of an EM field with a nanostructured metal surface also strongly influences other optical phenomena, namely absorption and luminescence. Surface-enhanced infrared absorption (SEIRA) of monolayers of benzoic acids on thin Ag island films was first observed in 1980s (Hartstein et al. 1980). The EM mechanisms is attributed to a local field enhancement and, correspondingly, to an enhancement of the absorption cross-section. Absorption can be enhanced generally by a factor of 10 -10 (Osawa 2001 Aroca 2006) and SEIRA is used as a complementary technique to SERS in some cases (Aroca 2006). 

Finally, it is evident that SERS should be considered from a wider perspective and comparing the performance of SERS with other techniques can always be useful. For example, fluorescence microscopy and spectroscopy are extremely sensitive and widely used techniques in many areas of the life sciences. Further development and expanding of other surface-enhanced spectroscopic techniques such as surface-enhanced infrared absorption (SEIRA), surface-enhanced fluorescence (SEF) and tip-enhanced Raman scattering (TERS) are also highly desirable. It is highly appreciable so that these techniques will help to refine information obtained by SERS in many bioanalytical, biomolecular and medical studies. 

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