Single metal nanoparticles quenching

The radiative and nonradiative decay rates depend also on a possible aggregation state of the dye molecules. The lifetime of aggregates can be longer than that of single molecules on the other hand, the fluorescence may be almost entirely quenched. Extremely strong effects on the decay rates must also be expected if dye molecules are bound to metal surfaces, especially to metallic nanoparticles [182,309, 337]. 

In two more recent papers on single molecule fluorescence near thin metallic layers, Enderlein reminds us that the quenching by metal nanoparticles shortens the lifetime of the excited state and by doing this, increases the number of excitation cycles that the molecule can survive before it is photobleached. This is an extremely important point, especially when dealing with single molecules, as fluorescence quantum yields are not nearly as important as the number of photons that are emitted before photobleaching occurs. 

In those cases, the ina-eased two photon absorption due to the field enhancement effect clearly outweighs the effects of fluorescence quenching. However, also these experiments had been carried out on submonolayer metallic films. Peleg et al. showed a decreased two photon fluorescence signal frcnn fluorophores close to single gold nanoparticles. ... 

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