Silver island films fluorophores

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. 

Figure 8. Schematic for a fluorophore solution between two silver island films. The solid ellipsoids represent the silver island films (Top). The effect of silver island films on the emission spectra of Rhodamine B (Middle) and Rose Bengal (Bottom). Adapted firom reference 17.

Figure 11. The effect of silver island films on the quantum yields of fluorophores. Adapted firan reference 17.

In recent years we have been reporting our observations on the favorable effects of silver nanoparticles deposited randomly on glass substrates (silver island films) for increasing the intensities and photostability of fluorophores, particularly those with low quantum yields. These reports described fluorophores with visible excitation and emission wavelengths. Since the fluorophores interact with metal through die surface plasmon resonance, for-silver the absorption maximum is near 430 nm, we did not know if silver particles would enhance the emission of ICG with absorption and emission... 

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