Dyes, surface Raman scattering

The enhancement of the surface Raman scattering of dyes at their resonance (which may be shifted on the surface as compared to solution) is that of normal Raman scatterers. 

Kneipp K, Kneipp H, Deinum G, Itzkan I, Dasari R R and Feld M S 1998 Single-molecule detection of a cyanine dye in silver colloidal solution using near-infrared surface-enhanced Raman scattering App/. Spectrosc. 52 175-8... 

Utilization of resonance effects can facilitate unenhanced Raman measurement of surfaces and make the technique more versatile. For instance, a fluorescein derivative and another dye were used as resonantly Raman scattering labels for hydroxyl and carbonyl groups on glassy carbon surfaces. The labels were covalently bonded to the surface, their fluorescence was quenched by the carbon surface, and their resonance Raman spectra could be observed at surface coverages of approximately 1%. These labels enabled assess to changes in surface coverage by C-OH and C=0 with acidic or alkaline pretreatment [4.293]. 

We also tried measurements to demonstrate that hot spots make significant contributions to surface enhanced Raman scattering [34]. For this purpose, the sample of nanoparticie assembly was doped with Raman active molecules by a spincoating method, and near-field excited Raman scattering from the sample was recorded. We adopted Rhodamine 6G dye as a Raman active material, which is... 

DoeringW.E., Nie S.M., Spectroscopic tags using dye-embedded nanoparticles and surface-enhanced Raman scattering, Anal. Chem. 2003 75 6171-6176. 

Another method for assaying the activity and stereoselectivity of enzymes at in vitro concentrations is based on surface-enhanced resonance Raman scattering (SERRS) using silver nanoparticles (116). Turnover of a substrate leads to the release of a surface targeting dye, which is detected by SERRS. In a model study, lipase-catalyzed kinetic resolution of a dye-labeled chiral ester was investigated. It is currently unclear how precise the method is when identifying mutants which lead to E values higher than 10. The assay appears to be well suited as a pre-test for activity. 

Li et al. have performed a comparative study on the surface-enhanced resonance hyper-Raman scattering and surface-enhanced resonance Raman scattering (SERRS) of dyes adsorbed on Ag electrode and Ag colloid [210]. 

Surface-enhanced resonance Raman scattering (SERRS) has also been achieved using silver colloid aggregates produced in situ in the chip. This method was used to detect an azo dye, 5-(2,-methyl-3,5,-dinitrophenylazo)quinolin-8-ol, which is a derivative of the explosive, TNT. With this method, it was possible to detect 10 iL of 10 9 M dye (or 10 fmol). This represented a 20-fold increase in sensitivity over that achieved using a macro flow cell [739]. 

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. 

Ingram A, Stokes RJ, Redden J, Gibson K, Moore B, Faulds K, Graham D (2007) 8-hydroxyquinolinyl azo dyes a class of surface-enhanced resonance Raman scattering-based probes for ultrasensitive monitoring of enzymatic activity. Anal Chem 79 8578-8583... 

Munro CH, Smith WE, White PC (1995) Qualitative and semi-quantitative trace analysis of acidic monoazo dyes by surface enhanced resonance Raman scattering. Analyst 120 993-1003... 

The estimate of the degree of enhancement in every one of our experiments is of prime importance for understanding SERS. First, the enhancement factors vary from system to system and that may reflect different contributions of the various possible mechanisms. Second, the sensitivity of the Raman systems has improved thus, detection of a signal does not necessarily mean that an enhancement of four to six orders of magnitude occurs. Nowadays one can detect signals which are enhanced by a factor of only 100 to 1000 or less. The Raman scattering of dyes adsorbed on surfaces can be detected even without any enhancement at all. 

Pemberton and Buck " studied the adsorption on a silver electrode of diphenylthiocarbazone anion (HDz ), a dye with its absorption maximum at 470 nm. An ORC was not carried out. Again, the enhancement was not evaluated. However, if one compares the surface spectra obtained, to those reported for a gold electrode using 488-nm light, it is immediately clear that the Raman scattering is hardly surface enhanced at all on silver, as it is not, at least at this excitation, at gold. 

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