Fluorescence resonance Rayleigh scattering

Nanomaterials in the form of a colloidal solution or quantum dots are attributed to have a tremendous impact in analytical chemistry for their unique physical and chemical properties (Alivisatos 2004 Katz and Willner 2004). A different methodology has been adopted to analyse vitamin Bi spectro-fluorimetrically by using cadmium selenide quantum dots (CdSe QDs), cadmium telluride (CdTe) nanorods, and silica and gold nanoparticles. A fluorescence resonance Rayleigh scattering (RRS) method was applied for determining vitamin Bi at sub-nanomolar level (Liu et al. 2006). In this technique, vitamin Bi was mixed with acidic buffer and prepared gold nanoparticles. After incubation, the solution mixture was excited in synchronous mode to obtain RRS spectra. The RRS spectral intensity correlated with the concentration of vitamin Bi. 

Dark-field spectroscopy (DFS) Dark-field spectroscopy, also known as resonant Rayleigh scattering spectroscopy (RRSS), is a technique that correlates the LSPR of single nanoparticles to enhancements in fluorescence and Raman scattering. 

J. L. Carlsten and A. Szoke. Spectral resolution of near-resonant Rayleigh scattering and collision induced resonance fluorescence. Phys. Rev. Lett., 56 667-671 (1976). 

J. Fiutak and J. van Kranendonk. The effect of collisions on resonance fluorescence and Rayleigh scattering at high intensities. J. Phys. B, 73 2869-2884 (1980). 

Liu, S. Feng, P. Resonance Rayleigh scattering for the determination of berberine in tablet form with some acidic xanthene fluorescent dyes original paper. Mikrochim. Acta 2002, 140, 189-193. 

Figure 7.1 Energy level diagram Illustrating changes that occur in IR, normal Raman, resonance Raman, and fluorescence. Notation on the figure stands for Rayleigh scattering (R), Stokes Raman scattering (S), and anti-Stokes Raman scattering (A). Reprinted from Ferraro et al. (2003) [4] with permission from Elsevier.

Rayleigh scattering is an ever present interference for any resonant fluorescence component and will set the ultimate lower limit on detectability. It is generally very small though and and has the property of being highly polarized. This property... 

These contradictory results led Jonkman et al.21 to propose that non-resonant light scattering (NRLS) was responsible for the fast component. NRLS would yield decays that basically consisted of Raman-Rayleigh-scattered laser light together with the slower fluorescence decay. It would look like biexponential decay. Experiments where the laser was purposely detuned from the rotational line seemed to confirm their ideas.21... 

Figure Bl.2.5. Comparison of several light seattering processes, (a) Rayleigh scattering, (b) Stokes and anti-Stokes Raman scattering, (c) pre-resonance Raman scattering, (d) resonance Raman scattering and (e) fluorescence where, unlike resonance Raman scattering, vibrational relaxation in the excited state takes place. From [3], used with permission.

Measurement of Self-Diffusion Coefficient What is measured in DLS is D. DLS cannot measure because it does not distinguish one solute from another. It is necessary to use other more specialized techniques such as forced Rayleigh scattering (FRS), fluorescence recovery after photo-bleaching (FRAP), and pulsed-field gradient nuclear magnetic resonance (PFG-NMR). 

However, Raman spectrum shows weak signal intensity compared with conventional Rayleigh scattering and fluorescence, which is a widely used technique for molecular detection. Raman scattering cross-sections imply that the scattering intensities are between 10 and 10 cm/molecule (for comparison, the maximum fluorescence cross-section is 10 cm /molecule). Resonance Raman scattering (RRS) can increase the cross-section when a molecule is excited by a laser with a resonance frequency. However, RSS still has an insufficient... 

---