Surface Enhanced Raman chemical enhancement

Surface-enhancement Electromagnetic and chemical effects can enhance the Raman intensities from substances in close proximity to appropriate metal surfaces by several orders of magnitude. 

Alak AM, Vo-Dinh T. 1987. Surface-enhanced raman spectrometry of organophosphorus chemical agents. Anal Chem 59 2149-2153. 

Of special Interest as O2 reduction electrocatalysts are the transition metal macrocycles In the form of layers adsorptlvely attached, chemically bonded or simply physically deposited on an electrode substrate Some of these complexes catalyze the 4-electron reduction of O2 to H2O or 0H while others catalyze principally the 2-electron reduction to the peroxide and/or the peroxide elimination reactions. Various situ spectroscopic techniques have been used to examine the state of these transition metal macrocycle layers on carbon, graphite and metal substrates under various electrochemical conditions. These techniques have Included (a) visible reflectance spectroscopy (b) laser Raman spectroscopy, utilizing surface enhanced Raman scattering and resonant Raman and (c) Mossbauer spectroscopy. This paper will focus on principally the cobalt and Iron phthalocyanlnes and porphyrins. 

Interfacial water molecules play important roles in many physical, chemical and biological processes. A molecular-level understanding of the structural arrangement of water molecules at electrode/electrolyte solution interfaces is one of the most important issues in electrochemistry. The presence of oriented water molecules, induced by interactions between water dipoles and electrode and by the strong electric field within the double layer has been proposed [39-41]. It has also been proposed that water molecules are present at electrode surfaces in the form of clusters [42, 43]. Despite the numerous studies on the structure of water at metal electrode surfaces using various techniques such as surface enhanced Raman spectroscopy [44, 45], surface infrared spectroscopy [46, 47[, surface enhanced infrared spectroscopy [7, 8] and X-ray diffraction [48, 49[, the exact nature of the structure of water at an electrode/solution interface is still not fully understood. 

A large number of possible applications of arrays of nanoparticles on solid surfaces is reviewed in Refs. [23,24]. They include, for example, development of new (elect-ro)catalytical systems for applications as chemical sensors, biosensors or (bio)fuel cells, preparation of optical biosensors exploiting localized plasmonic effect or surface enhanced Raman scattering, development of single electron devices and electroluminescent structures and many other applications. 

Guo, L., Huang, Q., Li, X. and Yang, S. (2001) Iron nanoparticles synthesis and applications in surface enhanced Raman scattering and electrocatalysis. Physical Chemistry Chemical Physics, 3, 1661-1665. 

Rodger, C., Smith, W.E., Dent, G. and Edmondson, M. (1996) Surface-enhanced resonance-Raman scattering an informative prohe of surfaces. Journal of the Chemical Society Dalton Transactions, 791—799. 

Narayanan V., Begun G., Stokes D., Sutherland W., Vo-Dinh T., Normal Raman and surface-enhanced Raman scattering (SERS) spectra of some fungicides and related chemical compounds,/. Raman Spectrosc., 1992 23 281-286. 

Murphy T., Schmidt H., Kronfeldt H., Use of sol-gel techniques in the development of surface-enhanced Raman scattering (SERS) substrates suitable for in situ detection of chemicals in sea-water, Appl. Phys. B, 1999 69(2) 147-150. 

Vo-Dinh T., Surface-Enhanced Raman Spectrometry, in Chemical Analysis of Polycyclic Aromatic Compounds, Vo-Dinh T. ed., Wiley, New York (1989). 

Li Y.S., Vo-Dinh T., Stokes D.L., Yu W., Surface-enhanced Raman analysis of p-nitroaniline on vacuum evaporation and chemically deposited silver-coated alumina substrates,Appl. Spectrosc 1992 46 1354-1357. 

Li Y.S., Wang Y., Chemically prepared silver alumina substrate for surface- enhanced Raman-scattering, 4/ /)/. Spectrosc 1992 46 142-146. 

The use of surface-enhanced resonance Raman spectroscopy (SERRS) as an identification tool in TLC and HPLC has been investigated in detail. The chemical structures and common names of anionic dyes employed as model compounds are depicted in Fig. 3.88. RP-HPLC separations were performed in an ODS column (100 X 3 mm i.d. particla size 5 pm). The flow rate was 0.7 ml/min and dyes were detected at 500 nm. A heated nitrogen flow (200°C, 3 bar) was employed for spraying the effluent and for evaporating the solvent. Silica and alumina TLC plates were applied as deposition substrates they were moved at a speed of 2 mm/min. Solvents A and B were ammonium acetate-acetic acid buffer (pH = 4.7) containing 25 mM tributylammonium nitrate (TBAN03) and methanol, respectively. The baseline separation of anionic dyes is illustrated in Fig. 3.89. It was established that the limits of identification of the deposited dyes were 10 - 20 ng corresponding to the injected concentrations of 5 - 10 /ig/ml. It was further stated that the combined HPLC-(TLC)-SERRS technique makes possible the safe identification of anionic dyes [150],... 

In addition to the indirect experimental evidence coming from work function measurements, information about water orientation at metal surfaces is beginning to emerge from recent applications of a number of in situ vibrational spectroscopic techniques. Infrared reflection-absorption spectroscopy, surface-enhanced Raman scattering, and second harmonic generation have been used to investigate the structure of water at different metal surfaces, but the pictures emerging from all these studies are not always consistent, partially because of surface modification and chemical adsorption, which complicate the analysis. 

Surface-enhanced resonance Raman spectra were observed from dye molecules spaced as distant as six spacer increments (ca. 16 nm = 16 A) from the silver surface. These studies suggested that an electromagnetic mechanism is operative in this assembly in contradistinction to a chemical mechanism that would require direct contact between the Raman-active species and the metal surface. These studies are of relevance in the study of chromophoric species in biological membranes (e.g., enzymes, redox proteins, and chlorophylls). 

The reaction between A-chlorobenzotriazole and l-methyl-2-phenylindole involves formation of the indole radical cation and benzotriazole radical via an initial electron transfer <82JOC4895, 91JCS(P2)1779>. Chemical reactions of benzotriazole on a freshly etched surface of metallic copper are studied by surface-enhanced Raman scattering, x-ray photoelectron spectroscopy, and cyclic voltammetry. The surface product is (benzotriazolato)copper(-l-), which covers the surface in the shape of polymeric material and shows good anticorrosion effects for copper <91JPC7380>. 

Kambhampati, R, Child, C. M., Foster, M. C., and Campion, A. 1998. On the chemical mechanism of surface enhanced Raman scattering Experiment and theory. J. Chem. Phys. 108 5013-26. 

Campion A, Kambhampati P. Surface-enhanced Raman scattering. Chemical Society Reviews 1998, 27, 241-250. 

Yang WH, Hulteen JC, Schatz GC, Van Duyne RP. A surface-enhanced hyper-Raman and surface-enhanced Raman scattering study of tra ,s-l,2-bis(4-pyridyl)ethylene adsorbed onto silver film over nanosphere electrodes. Vibrational assignments experiment and theory. Journal of Chemical Physics 1996, 104, 4313 -323. 

Van Duyne RP, Hulteen JC, Treichel DA. Atomic force microscopy and surface-enhanced Raman spectroscopy. I. Ag island films and Ag film over polymer nanosphere surfaces supported on glass. Journal of Chemical Physics 1993, 99, 2101-2115. 

Liao PF, Bergman JG, Chemla DS, Wokaun A, Melngailis J, Hawryluk AM, Economou NP. Surface-enhanced Raman scattering from microlithographic silver particle surfaces. Chemical Physics Letters 1981, 81, 355-359. 

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