Rhodamine Raman spectrum

Yan et al. [71] have used a hollow photonic crystal fiber bundle to immobilize multifaceted AuNPs of 100-200 nm diameters within the hollow stmcture (Fig. 12). They launched the excitation light at 633 nm for Raman spectroscopy onto the end fire of the photonic crystal fiber with a x50 objective. The same objective lens was used to collect the scattered light for Raman spectroscopy. The sensing material or analyte was rhodamine B immobihzed and dried within the photonic fiber onto the AuNPs. The Raman spectrum showed a clear surface enhancement in the presence of the AuNPs. Nevertheless the authors used a photonic crystal fiber, no band gap... 

Figure 7 shows a good example of a crucial advantage of SERRS, namely fluorescence quenching. In this figure, the SERRS spectrum of rhodamine 6G is recorded and, with it, the attempt to obtain a resonance Raman spectra from the same concentration. These spectra were recorded using 514-nm radiation, and fluorescence completely obscures the resonance Raman spectrum, but due to the fluorescence being quenched, the SERRS from rhodamine 6G is clearly observed. Fluorescence can be a particular problem in forensic... 

Figure 1.5. Spectra of rhodamine 6G obtained with a 514.5 nm laser and dispersive spectrometer (upper) or an FT-Raman spectrometer and 1064 nm laser (lower). Intensity scales differ greatly, with the upper spectrum being much more intense.

The first approach toward SMD using surface-enhanced resonance Raman scattering was published by Kneipp et al. in 1995 [58]. It involves the use of extremely low dye concentrations (down to 10 M of rhodamine 6 g) adsorbed at silver colloids which were activated by NaCl. The authors estimated that less than 100 dye molecules were enough for recording an SERS spectrum with sufficient signal-to-noise ratio. 

Figure 2 Resonance Raman and SERBS spectra of rhoda-mine 6G with excitation at 514.5 nm, The high fiuorescence background is effectiveiy quenched in the SERRS spectrum due to adsorption of the rhodamine onto the surface of the siiver nanoparticies, (Reproduced with permission from Rodger C and Smith WE (2002) SERS. in Handbook of Vibrational Spectroscopy. New York Wiiey John Wiiey Sons Ltd.)...

Figure 3 Curve a Solution speotrum from a 10- M Rhodamine 6G solution using 514.5 nm exoitation, demonstrating the predominance of fluorescence over resonance Raman scattering. Curve b SERRS spectrum taken from a suspension of aggregated silver colloid to which 150 pL of a 10 M Rhodamine 6G solution has been added using 514.5 nm excitation.

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