Fluorophore absorption band, metallic

The detected fluorescence can be significantly enhanced, however, by exploiting the plasmonic enhancement which can occur when a metal nanoparticle (NP) is placed in the vicinity of a fluorescent label or dye [1-3]. This effect is due to the localised surface plasmon resonance (LSPR) associated with the metal NP, which modifies the intensity of the electromagnetic (EM) field around the dye and which, under certain conditions, increases the emitted fluorescence signal. The effect is dependent on a number of parameters such as metal type, NP size and shape, NP-fluorophore separation and fluorophore quantum efficiency. There are two principal enhancement mechanisms an increase in the excitation rate of the fluorophore and an increase in the fluorophore quantum efficiency. The first effect occurs because the excitation rate is directly proportional to the square of the electric field amplitude, and the maximum enhancement occurs when the LSPR wavelength, coincides with the peak of the fluorophore absorption band [4, 5]. The second effect involves an increase in the quantum efficiency and is maximised when the coincides with the peak of the fluorophore emission band [6]. 

Localized surface plasmon resonance (LSPR) at the metal surface has been exploited to enhance the signal obtained from optical biochips and thereby lower the limits of detection. There are two main enhancement factors (i) an increase in the excitation of the fluorophore by localizing the optical field on the nanoparticles near the fluorophore and (ii) an increase in quantum efficiency of the fluorophore. The plasmon resonance wavelength should coincide with the fluorophore absorption band to obtain the maximum emission efficiency. Several parameters concerning the signal detection enhancement are as follows (84)... 

The utilizatirHi of DBI (5-dimethylamino-2-(2-pyridinyl)-benzoiinidazole) as a fluorophore is another approach for the development of Cd -selective ICT probes [66], Metal complexation with the DBI core occurs by chelation of the metal with the 2,2 -N atoms this leads to co-planation of the pyridine and benzoimidazole moieties in DBI with consequent stabilization of the ICT stmcture. In this case, unlike CadMQ, red-shifted bands are observed in both the absorption and emission spectra. Free DBITA (13, Figure 4) exhibits an absorption band at 340 nm in an HEPES buffer solution (pH = 7.2), whereas this band is red-shifted to 359 nm... 

The preceding chapter showed that many different processes have to be considered if one would like to fully understand the interactions between a fluorophore and a nanostructured metallic template. Depending on the distance regime, classical image theory, electrodynamic theory, nonlocal effects or even wave functions of conduction band electrons leaking out of the metal surface have to be considered. Furthermore, each of the theories gives different results for fluorophores oriented perpendicular or tangential to the metallic surface. Different situations are also expected when either the absorption spectrum or the emission spectrum of the fluorophore overlaps with the plasmon... 

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