Silver island films metal-enhanced fluorescence

A number of promising metal structures for fluorescence signal enhancement have been proposed silver island films (SIFs) that provide about 5-15-fold enhancement [89], fractal-like structures that resulted in stronger enhancements at specific hot spots [90-92], and SIFs deposited on silver or gold films with about 50-fold enhancement [93, 94], Recently, it was found that strong enhancement on a gold film based plasmonic platform may change even the shape of the emission spectrum [95],... 

K. Aslan, Z. Leonenko, J. R. Lakowicz, and C. D. Geddes. Annealed silver-island films for applications in metal-enhanced fluorescence Interpretation in terms of radiating plasmons yourna/ of fluorescence, 2005, 15, 643-654. 

K. Aslan, S. N. Malyn, and C. D. Geddes. Angular-Dependent Metal-Enhanced Fluorescence from Silver Island Films Chemical physics letters, 2008,453, 222-228. 

Ray, K., Badugu, R., and Lakowicz, J. R. (2007). Sulforhodamine Adsorbed Langmuir-Blodgett Layers on Silver Island Films Effect of Probe Distance on the Metal-Enhanced Fluorescence. Journal of Physical Chemistry C 111 7091-7097. 

Aslan, K., Malyn, S. N. and Geddes, C. D. (2008). Angular-dependent metal-enhanced fluorescence from silver island films. Chem. Phys. Lett. 453 222-228. 

Sulforhodamine adsorbed Langmuir-Blodgett layers on silver island films effect of probe distance on the metal-enhanced fluorescence. J. Phys. Chem. 

Figure 10.9 Sample architecture for the distance dependence of metal-enhanced Superoxide generation (Top), and graphical representation of the interpretation of metal-enhanced superoxide generation with an enhanced and distance dependent excitation rate (Bottom). F - Fluorophore, MEF - Metal-Enhanced Fluorescence, MEP — Metal-enhanced Phosphorescence, SiFs — Silver Island Films. EF- Enhancement factor = I Silver /I Glass. Adopted from ref [31 ].

Both Geddes and the Lakowicz group s have investigated the metal-enhanced fluorescence of fluorophores on silver island films (SIFs) [11,26,27] and variously aggregated silver nanoparticles in solution [28,29]. One example of enhancement on SIFs is discussed below [26]. In this work the distance-dependent MEF of a monolayer of sulforfiodamine B (SRB) on SIFs was studied. A SRB monolayer was electrostatically incorporated into the Langmuir-Blodgett (LB) layers of octadecylamine (ODA) deposited... 

In addition to the field enhancement, the increases of the radiative decay rate of the molecule also lead to the fluorescence enhancement. This happens when molecules are S -20nm away from metal nanoparticies aggregated on surfaces [19-21]. Lakowicz and coworkers have characterized this phenomena by using silver island films deposited on the internal surface of two quartz plates which sandwich a bulk fluorophore solution [20]. The fluorophores are physically placed close to silver islands so that there are a range of distances between the fluorophore and metal. The fluorescence enhancement is accompanied by decreased lifetimes and increased photostability. This phenomenon shows that the silver island increases the radiative decay rate of the fluorophore and therefore induces the fluorescence enhancement. 

In 1988, the distance dependence of surface-enhanced fluorescence was studied for Langmuir-Blodgett monolayers deposited on silver island films. This study was inspired in part by two earlier reports that examined the distance dependence of SERS of LB films on metal surfaces. Varying numbers of spacer layers of arachidic acid were employed in order to probe the competition between EM enhancement and radiationless energy transfer for a phthalocyanine monolayer. In direct contact with the metal surface, a broadened, enhanced, and red-shifted fluorescence spectrum was observed. These spectral changes can be attributed to a drastic decrease in the fluorescence lifetime of the molecule when it is placed in contact with the metal surface. However, an enhanced version of the unperturbed spectrum was observed when intervening spacer layers were introduced. It was found at enhancements on the order of about 400 could be realized when S monolayers were placed between the Ag island film and the phthalocyanine monolayer. 

Aslan, K., Leonenko, Z., Lakowicz, J. and Geddes, C. (2005) Aimealed silver-island films for appUcations in metal-enhanced fluorescence interpretation in terms of radiating plasmons. Journal of Fluorescence, 15, 643 54. 

---