Surface plasmon field-enhanced light

Fundamentals. Surface plasmons (SP) can be used to monitor optical properties of metal and semiconductor surfaces. For introductory overviews, see [969, 970]. Surface plasmon field-enhanced light scattering (SPFELS) is observed when an interface is illuminated by light under conditions stimulating surface plasmon excitation as reported [971]. 

Fig. 5.155. Cyclic voltammogram of polyaniline and surface plasmon field-enhanced light scattering with a solution of 0.5 M H2SO4, second scan, dE jdt — 20 mV-s based on data in [971]...

SPFELS Surface plasmon field enhanced light scattering... 

If one includes the employment of evanescent light waves in spectroscopic studies in the near-field area. Knoll and coworkers are among the first who reported on near-field Raman spectroscopy , though this approach was termed at that time (the early 1990s) as surface plasmon field-enhanced Raman spectroscopy and microscopy [104],... 

In an attempt to overcome this limit of detection we recently introduced surface plasmon field-enhanced fluorescence spectroscopy (SPFS) following an earlier report liy Attridge et al. The basic principle of this approach combines the excitation of a surface plasmon mode as an interfacial light source with the well-established detection schemes of fluorescence spectroscopy the resonantly excited surface plasmon waves excite chromophores that are attached to the analyte either chemically or by genetic engineering techniques. The emitted fluorescence photons are then monitored and analyzed in the usual way to give information about the behavior of the analyte itself. 

Baba, A. Xia, C. Knoll, W. Advincula, R. C., Electrochemical Surface Plasmon Resonance and Field-Enhanced Light-Scattering Monomer Copolymerization... 

Metal nanoparticles have attracted considerable interest due to their properties and applications related to size effects, which can be appropriately studied in the framework of nanophotonics [1]. Metal nanoparticles such as silver, gold and copper can scatter light elastically with remarkable efficiency because of a collective resonance of the conduction electrons in the metal (i.e., the Dipole Plasmon Resonance or Localized Surface Plasmon Resonance). Plasmonics is quickly becoming a dominant science-based technology for the twenty-first century, with enormous potential in the fields of optical computing, novel optical devices, and more recently, biological and medical research [2]. In particular, silver nanoparticles have attracted particular interest due to their applications in fluorescence enhancement [3-5]. 

Figure 19.1 (A) 2D projection of the calculated local field intensity distribution around a pair of 15 nm diameter silver nanoparticles excited with Xi = 400 nm light polarized along the interpaiticle axis. The edge-to-edge particle separation is 2 nm and the free space incident light intensity Ej,x P taken to be unity. The local field intensity near the pair is shown in false color. The calculation was done using dipole-dipole approximation (DDA) method with each dipole unit being a square with sides of 0.2 nm. (B) Model of the photophysics of a molecule represented by a three level system and how the excitation and decay dynamics are affected by plasmon enhancement of radiative rates and the introducticm of a rate for quenching Icq of the excited state due to proximity to the metal surface. E (X ) and E (X2) are the field enhancements at the position of the molecule for the excitation and emission wavelengths respectively, kn and kMR represent the radiative and non-radiative decay rates of the molecule in the absence of plasmon enhancement.

The field reaches its maximum at the surface plasmon resonance frequency when e = -2 Co where Co is the dielectric constant of the medium surrounding the particle surface. This induced field of the metallic nanoparticies provides an external field for the fluorescence excitation of the molecules in addition to the electric field of the incident light and thus increases the absorption rate which is responsible for the enhanced fluorescence intensity. 

For electromagnetic enhancement the exciting laser light must first couple to the metal surface to produce a surface plasmon. A surface plasmon is an interaction between free surface charges and the electromagnetic field [26-28] (Figure... 

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