How Gold Particles Suppress Concentration Quenching of Fluorophores Encapsulated in Silica Beads

Increasing the luminescence of silica particles encapsulating fluorescein by increasing fluorescein concentration is a promising strategy which is unfortunately limited by the phenomenon of self-quenching. In this paper, we demonstrate that this quenching can be almost entirely suppressed by the presence of gold inclusions within silica. Precisely, in core(gold)/shell(polysiloxane) particles incorporating fluorescein molecules, the quantum yield attains 80% of that of isolated fluorescein for an interdye distance of 3 nm whereas it is less than 15% in the absence of gold. From systematic measurements of quantum yield and lifetime, we proved that, contrary to all literature expectations, the reduction of self-quenching does not originate from the enhancement of the radiative decay rate but from a dramatic decrease of the nonradiative one: the presence of metal inclusions impeding energy transfers to fluorescein H-type dimers that act as traps for light.