SEIRA and SERS

As in usual IR and Raman spectroscopy, SEIRAS and SERS are complementary to each other, and thus a comparison of SEIRA and SER spectra is valuable for a better understanding of the both spectra. Comparisons of SEIRA and SER spectra were reported for p-nitroaminothiol and pyrazine adsorbed on polycrystalline Ag and Au surfaces, respectively [70, 71]. 

In Fig. 8.11, the observed SER bands of pyrazine adsorbed on Au electrodes are compared with the normal IR spectrum of an aqueous pyrazine solution (5 M) and the SEIRA spectrum of adsorbed pyrazine [71]. In the SER spectrum (c), the Raman-inactive modes for the free molecule are observed at 1479, 1155, 1123, and 1047 cm (shown by dashed lines) together with Raman-active modes (sohd lines). The counterparts of these Raman-inactive modes can be found in the solution IR spectrum (a), indicating that these bands are apparently ungerade modes. On the other hand, the SEIRA spectrum (b) is essentially identical to the solution 

---

To prevent denaturation of redox proteins and enzymes upon immobilization on an electrode surface that is necessary for electrochemical investigations, electrodes may have to be modified with suitable biocompatible membranes. Studies of redox processes and associated non-electrochemical processes of bound species with both SEIRAS and SERS have been reviewed [326]. 

SEIRA and SERS are powerful techniques for stmctural characterization of ultra thin films and well-ordered monolayer on metal surfaces. Thin films at interfaces are prepared by different procedures and developed for various applications. The fabrication and characterization of ultra thin films is a permanent area of research where some of the most interesting subjects are (a) bilayers and monolayers at liquid-liquid interface, (b) adsorption monolayers and Langmuir (water-insoluble) monolayers at air-water interface, (c) adsorption films and self-assembled monolayers (SAMs) at liquid-solid interface and Langmuir-Blodgett Alms, cast (deposit) films and spin-coat films at air-solid interface. Studies about molecular organization of monolayers of porphyrins derivatives, of azamacrocy-cles and their metallic derivatives among the many SEIRA applications to films and interfaces, were published . 

The RAIRS, SEIRA and SERS spectra of the Ni(II) (franv-7,14-dimethyl-5,12,-diphenyl-1,4,8,1 l-tetraaza-2,3-9, lO-dinaphthyl-cyclotetradeca-5,7,12,14-tetraene) (NiN4 2) and Cu(II) (5,7,12,14-tetramethyl-l,4,8,1 l-tetraaza-2,3-9, 10-dinaphthyl-cyclotetradeca-5,7,12,14-tetraene) (CUN4) in Figure 14.19, were reported. For the RAIRS analysis, complexes were deposited onto a smooth copper surface and onto a KBr monocrystal. Both spectra were compared with the spectrum of the complex dispersed in KBr. No substantial frequency differences between them were observed, pointing out that the surface does not markedly influence the corresponding complex structure. 

The complementary nature of the information provided by SEIRA and SERS is illustrated in the spectra of the DCEC/PYR complex. SERS spectra are mainly dominated by PYR bands. Thus, SERS can be used to follow the changes occurring in the PAHs as a consequence of the interaction with the calixarene host and for detection purposes. 

Thus, the infrared and SEIRA, Raman and SERS and IRRAS measurements allow us to determine the most probable orientation of the molecules onto different metal surfaces, to infer about the influence that these surfaces have onto the molecular structure and to conclude about the mechanism governing the spectral enhancement in IR and Raman. 

The FT-Raman spectra and SERS on silver colloid of the azabipiridyl ligand and its Co(II), Ni(II) and Cu(II) complexes was reported a SEIRA study was also accomplished. ... 

A related effect has been described for IR spectroscopy - Surface Enhanced Infrared Absorption spectroscopy (SEIRA). However, as the enhancement factors are significantly lower than for SERS and both the required metal particle size and the activation distance between the target molecule and the particle are more than one order of magnitude smaller, no practically applicable SEIRA sensors have been demonstrated up to now. 

CN-C6H4-NC One NC group bonded to surface in p mode the second one is free and remote from the surface 2127 2129 uncoord NC 2180 coord NC 2184 coord NC SERS SERS SEIRA [38] [48]... 

Sampling in surface-enhanced Raman and infrared spectroscopy is intimately linked to the optical enhancement induced by arrays and fractals of hot metal particles, primarily of silver and gold. The key to both techniques is preparation of the metal particles either in a suspension or as architectures on the surface of substrates. We will therefore detail the preparation and self-assembly methods used to obtain films, sols, and arrayed architectures coupled with the methods of adsorbing the species of interest on them to obtain optimal enhancement of the Raman and infrared signatures. Surface-enhanced Raman spectroscopy (SERS) has been more widely used and studied because of the relative ease of the sampling process and the ready availability of lasers in the visible range of the optical spectrum. Surface-enhanced infrared spectroscopy (SEIRA) using attenuated total reflection coupled to Fourier transform infrared spectroscopy, on the other hand, is an attractive alternative to SERS but has yet to be widely applied in analytical chemistry. 

Fig. 8.11 Comparison of the normal infrared spectrum of (a) 5 M aqueous solution of pyrazine and (b) SEIRA spectrum of pyrazine adsorbed on an Au thin-film electrode at 0.0 V (vs SCE) [71], (c) SER bands of pyrazine adsorbed on a polycrystalline Au electrode taken from Ref [77]. The solid and...

As noted above, previous reports of the SEIRA effect had attributed the enhancement to a similar mechanism similar to the one leading to the SERS effect, namely the excitation of surface plasmon polaritons. " Because the effect was observed with Ni, Pt and Pd as well as Ag, Nakao and Yamada recognized that the effect that they observed was caused by some mechanism other than the effect of excitation of surface plasmon polar-itons. Nakao and Yamada postulated that the effect of multiple reflection in the metal film, of the decrease in penetration depth of the IRE caused by the metal layer and/or the effect of local (chemical) interaction at the metal-sample interface might contribute to the enhancement. However, as will be discussed later in this chapter, none of these putative causes fully explains the enhancement. 

In the early 1980s, despite the discovery of the surface-enhanced Raman (SER) effect [97] (see also Chapter 3.6 in this volume), there was no real expectation that such enhancement effects would be observed in in situ infrared spectra. That this was not necessarily to be the case could be gleaned from papers such as that by Christensen and coworkers (98) on the polymerization of thiophene at a Pt electrode in acetonitrile, who observed a somewhat more intense absorption than expected from the thiophene adsorbed on the electrode prior to polymerization. Recently, an increasing number of papers have appeared on AIREs, primarily from Sun and coworkers [99, 100) and SEIRAS, from Osawa and coworkers [19, 26,46, 55, 58,60,101-106), a common factor of both effects is the enhancement of the infrared absorptions of adsorbed species. 

The (nonelectrochemical) SEIRAS effect was first reported by Hartstein and coworkers in 1980 [110], after which Suetaka and coworkers published a number of papers from 1982 exploiting Kretschmann coupling (Fig. la) to effect SPP excitation and the concomitant enhancement of the infrared absorptions of species adsorbed at the thin metal film electrode surface [69, 111-113], effectively SEIRAS. The authors commented that the short-range enhancement afforded by the technique enabled species at the metal-aqueous solution interfaces to be preferentially observed . Similarly, Neff and coworkers [48] reported the study of water at the electrode-electrolyte interface using SPP excitation. As with the SERS effect, SEIRAS is limited, so far, to the coinage metals [5,10]. 

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... 

Metal island surfaces of controlled mass thickness for the SERS and SEIRA experiments are obtained by sublimation of the metal onto different plates according to general procedures described. ... 

Aliquots of analyte solutions are added to colloidal solutions or deposited onto the metal island surfaces thin layer spectra are obtained after diluting the sample on the surface using an appropriate solvent. All the spectra are scanned after complete solvent evaporation. Samples for SERS and SEIRA are also prepared by vacuum evaporation of controlled mass thickness. 

For some time now, we have been working with many different perylene derivatives in the study of surface-enhanced spectroscopies such as SERS, SERRS, SEF, and SEIRA (surface-enhanced infiared absorption). These molecules show a very strong tendency towards aggregation at high concentrations, and often display excimer fluorescence in concentrated Langmuir-Blodgett monolayers. The surface-enhanced... 

---