Metal-enhanced fluorescence aggregates

Near-IR Metal Enhanced Fluorescence And Controlled Colloidal Aggregation... 

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. 

The effect of micellar aggregates on the luminescence of organic compounds can be easily explained, whereas the introduction of a metal ion in these microheterogeneous systems significantly increases the difficulty to rationalize the observed effects. In fact, the mechanisms which are operating in micellar-enhanced fluorescence of metal complexes have not been completely elucidated. However, neutral complexes appear to be protected against deactivation pathways by the surrounding micellar environment [1]. 

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