Gold Nanoparticles in Core–Polyelectrolyte–Shell Assemblies Promote Large Enhancements of Phthalocyanine Fluorescence

Abstract

We have incorporated gold nanoparticles into a core–polyelectrolyte–shell type of assembly with a coating lipid vesicle encapsulating a phthalocyanine dye. The supramolecular construct having polyelectrolyte layers as spacers between the particle’s surface and the phthalocyanine was designed to control the emission enhancement through the plasmonic antenna effect of gold nanoparticles. We have observed large emission enhancements, of about 3 orders of magnitude, for an optimum number of 13 to 15 polyelectrolyte layers. Such large emission enhancements were attributed to hot-spots formed by the clustering of gold nanoparticles during the process of layer-by-layer deposition of polyelectrolytes. Fluorescence lifetime imaging microscopy allowed a correlation of those large emission enhancements with shortening of emission lifetimes, as expected from the plasmonic enhancement of radiative and nonradiative rates. It has also shown that these polyelectrolyte-assembled clusters of gold nanoparticles are of submicrometric size, which makes these nano-objects promising for enhanced imaging or biosensing applications.