Raman scattering metal-enhanced fluorescence

Most models for SEF focus on the plasmonics, and treat the molecule as a classical dipole. While the plasmonics models increasingly give more realistic results for the plasmon observed in the system, the treatment of the molecule, and thus the molecule-metal system, is not always as well developed. In their 2005 paper, Johansson, Xu, and Kail [44] present a unified model of enhanced Raman scattering and enhanced fluorescence within the context of quantum optics. This model is easily modified to include the field enhancement (M) and decay enhancement (Md), which may be calculated through plasmonics methodology. 

This handbook presents a comprehensive overview on the physics of the plasmon-emitter interaction, ranging from electromagnetism to quantum mechanics, from metal-enhanced fluorescence to surface-enhanced Raman scattering, and from optical microscopy to the synthesis of metal nanoparticles, filling the gap in the literature of this emerging field. It is useful for graduate students as well as researchers from various fields who want to enter the field of molecular plasmonics. The text allows experimentalists to have a solid theoretical reference at a different level of accuracy and theoreticians to find new stimuli for novel computational methods and emerging applications. 

Cade NI, Ritman-Meer T, Kwaka K, Richards D (2009) The plasmonic engineering of metal nanoparticles for enhanced fluorescence and Raman scattering. Nanotechnology 20 285201... 

The extremely small cross sections for conventional Raman scattering, typically 10 111 to 10-25 cm2/molecule has in the past precluded the use of this technique for single-molecule detection and identification. Until recently, optical trace detection with single molecule sensitivity has been achieved mainly using laser-induced fluorescence [14], The fluorescence method provides ultrahigh sensitivity, but the amount of molecular information, particularly at room temperature, is very limited. Therefore, about 50 years after the discovery of the Raman effect, the novel phenomenon of dramatic Raman signal enhancement from molecules assembled on metallic nanostructures, known as surface-enhanced Raman spectroscopy or SERS, has led to ultrasensitive single-molecule detection. 

In the experiments presented here, the fluorophores are adsorbed directly onto the metallic (gold) NP surface. The fluorescence enhancement (if any) is therefore small and the MEF signal may accordingly be weak, especially for weak fluorophores like Rh6G at 633 nm. In fact, the MEF spectrum is accompanied by Raman peaks of comparable intensity (themselves enhanced through Surface Enhanced Raman Scattering, SERS). 

Johansson, P., Xu, H., and Kail, M. (2005). Surface-enhanced Raman scattering and fluorescence near metal nanoparticles. Phys. Rev. B 72 035427-1-17. 

The electromagnetic nature of surface-enhanced Raman scattering (SERS) and plasmon-enhanced fluorescence (PEF) involves resonant excitations of localized plasmons (LPs) in the near-field of nanosized noble metal particles or films, coupling them with surrounding scatterers and detection of their secondary emission in the far field. Employment of these plasmonic phenomena are proposed, for example, as a new approach to increase brightness of heavily labeled macromolecules [1]. 

Progress in technology of nanosized materials has renewed attention to surface-enhanced optical phenomena. The nanoscale metals, which have important applications in snrface-enhanced Raman scattering (SERS) [1], surface-enhanced fluorescence (SEF) [2, 3] and optoelectronic nanodevices are of particular interest. 

---