SERRS, analytical method

Surface enhanced resonance Raman scattering (SERRS) is an analytical technique with several advantages over competitive techniques in terms of improved sensitivity and selectivity. We have made great progress in the development of SERRS as a quantitative analytical method, in particular for the detection of DNA. However, one of the main advantages over fluorescence and other optical detection techniques is the ability to multiplex. 

Fundamental questions related to the electronic configuration of the open or colored forms and the number and structures of the photomerocyanine isomers are considered on the basis of the results of continuous-wave (stationary) and time-resolved (picosecond, nanosecond, and millisecond) Raman experiments. For spironaphthoxazine photochromic compounds, the Raman spectra may be attributed to the TTC (trans-trans-cis) isomer having a dominant quinoidal electronic configuration. Surface-enhanced resonance Raman spectroscopy (SERRS) is demonstrated as a new analytical method for the study of the photodegradation process in solution for nitro-BIPS derivatives. The development of this method could lead to the identification of the photoproducts in thin polymer films or sol-gel matrices and ultimately to control of degradation. 

The discovery and understanding of SERS was important not only because it made Raman a more viable analytical method but also because it introduced the concept of surface-enhanced spectroscopies in general. With the SERS precedent, surface-enhanced resonance Raman spectroscopy (SERRS) and surface-enhanced hyper-Raman spectroscopy (SEHRS) have both been discovered and put to use as analytical tools. In fact, enhancement factors as large as 10 have been measured in SEHRS experiments (see Section VII.B). This immense enhancement was only recently surpassed by the 10 " enhancement measured in single molecule SERS (see Section X). 

Since SERS and SERRS are substance specific, they are ideal for characterisation and identification of chromatographically separated compounds. SE(R)R is not, unfortunately, as generally applicable as MS or FUR, because the method requires silver sol adsorption, which is strongly analyte-dependent. SE(R)R should, moreover, be considered as a qualitative rather than a quantitative technique, because the absolute activity of the silver sol is batch dependent and the signal intensity within a TLC spot is inhomogeneously distributed. TLC-FTIR and TLC-RS are considered to be more generally applicable methods, but much less sensitive than TLC-FT-SERS FT-Raman offers p,m resolution levels, as compared to about 10p,m for FTIR. TLC-Raman has been reviewed [721],... 

The single molecule detection capacity of SERRS has been used to develop analytical techniques for DNA. These can use either a substrate or a colloid. In either case, this is most effective when the label is within the monolayer of the surface and hence the largest SERRS enhancement can be obtained. Methods have been developed that enable spatial separation of different events and their detection on a substrate. The use of SERS to monitor DNA hybridization of a fragment of the breast cancer susceptibility gene, BRCAl, on modified silver surfaces has been shown to be effective. 

Figure 1 Number of journal publications devoted to environmental applications of various Raman techniques as a function of years. The resurgence of normal Raman spectroscopy in the late 1990s due to the improvements in Raman instrumentation is obvious. Also, a recent increase in SERS applications can clearly be seen. Moreover, the maturity of Raman spectroscopy as an important analytical tool in the analysis of complex environmental mixtures is seen in the steady growth of hyphenated techniques involving Raman spectroscopy. Note that publications reporting the use of hyphenated techniques were included in the tally for both hyphenated techniques as well as the specific Raman method employed (i.e., NRS, RRS, and SERS). In addition, publications reporting the use of the SERRS technique were included in the tally for both RRS and SERS. Hence, the Total category is not always equal to the sum of the NRS, RRS, and SERS applications.

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