Surface Enhanced Raman metal colloids

Kerker M., Electromagnetic Model for Surface-Enhanced Raman-Scattering (Sers) on Metal Colloids, Accounts Chem. Res. 1984 17 271-277. 

Surface-enhanced Raman scattering (SERS) has emerged as a powerful technique for studying species adsorbed on metal films, colloidal dispersions, and working electrodes. SERS occurs when molecules are adsorbed on certain metal surfaces, where Raman intensity enhancements of ca. 105-106 may be observed. The enhancement is primarily due to plasmon excitation at the metal surface, thus the effect is limited to Cu, Ag, and Au, and a few other metals for which surface plasmons are excited by visible radiation. 

Y., Sato, O., and Fujishima, A. (2002) Metal-coated colloidal crystal film as surface-enhanced Raman scattering substrate. Langrnuir, 18, 5043-5046. 

Dou, X.M. and Ozaki, Y. (1999) Surface-enhanced Raman scattering of biological molecules on metal colloids basic smdies and applications to... 

This effect is known as surface enhanced Raman scattering (SERS) [10-12]. The SERS effect has been widely investigated for various molecules adsorbed on rough metallic surfaces or on metallic clusters in colloids. Reviews on this topic can be found in Refs. [12-15]. The enhancement of normally Raman-active modes is a consequence of the enhancement of the electric field of the incoming and scattered radiation in the vicinity of a rough metal film upon coupling with the dipolar plasmon resonances in the metal clusters. This enhancement affects molecules located up to even 10 nm away from the metal surface [11, 12]. The enhancement factors are essentially determined by the electronic properties of the metal and by the morphology of the metal film. 

Tessier PM, Velev OD, Kalambm- AT, Rabolt JF, Lenhoff AM, Kaler EW (2000) Assembly of gold nanostructured films templated by colloidal crystals and use in surface-enhanced Raman spectroscopy. J Am Chem Soc 122 9554 Yan H, Blanford CF, Holland BT, Parent M, Smyrl WH, Stein A (1999) A chemical synthesis of periodic macroporous NiO and metallic Ni. Adv Mater 11 1003 Von Freymann G, John S, Schulz-Dobrick M, Vekris E, Tetreault N, Wong S, Kitaev V, Ozin GA (2004) Tungsten inverse opals The influence of absorption on the photonic band structure in the visible spectral region. Appl Phys Lett 84 224 Denny NR, Han SE, Norris DJ, Stein A (2007) Effects of thermal processes on the structure of monolithic tungsten and tungsten alloy photonic crystals. Chem Mater 19 4563... 

Raman spectroscopy is not particularly surface sensitive but a surface enhanced Raman scattering (SERS) effect is observed on some metals (copper, gold, silver, nickel etc). On an appropriately prepared (roughened) surface or on metal colloids the surface coverage of molecules can be measured by Raman spectroscopy with high sensitivity. 

Surface-enhanced Raman spectroscopy has been used to investigate the physical and chemical processes of the porphyrins on surfaces in many scientific publications. Surface-reactions such as metallization, demetalization, aggregation, electrochemical redox and N-protonation of the porphyrins on colloids. 

In this work different deposition teehniques were evaluated for the addition of metal nanoparticles to a contaminated area for in situ surface enhanced Raman spectroscopy. Also metallic colloids were added to solutions for Raman characterization at 7 meters of standoff distance. The goal was to combine SERS and a Raman telescope for remote detection of materials at trace levels. 

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