NIR-emitting fluorescent gold nanoclusters doped in silica nanoparticles

In this paper we describe the synthesis and the optimisation of a new family of fluorescent core–shell nanoparticle using protein-stabilised gold nanoclusters. Fluorescent gold nanoclusters (<2 nm) entrapped in bovine serum albumin (BSA) protein were loaded in a 100 nm-silica nanoparticle with an optimal concentration of 3% (w/w). These nanoparticles kept the fluorescence properties of the metal clusters with a high Stokes shift and an emission in the near infrared region (λ = 670 nm). They were fully characterized and showed a high monodispersity and stability over more than 5 months. Steady-state fluorescence and lifetime measurements indicate the role of silica as a protective host to improve the photostability and the chemical stability of the fluorescent compound. This new label was taken up in tumor lung cells and tracked by a confocal microscope to show the great potential of this biolabel for sensing and imaging.