NIR-Emitting Gold Nanoclusters Encapsulated in Photo-RAFT-PISA Polymer Nanoparticles for Bioimaging

Gold nanoclusters (AuNCs) were successfully encapsulated into hairy polymer nanoparticles produced by polymerization-induced self-assembly mediated by the reversible addition–fragmentation chain transfer process (RAFT-PISA), leading to near-infrared (NIR)-emitting biocompatible optical probes. AuNCs are a promising class of gold nanomaterials with a diameter below 2 nm and size-tunable photoluminescence. In addition, AuNCs usually feature long photoluminescence lifetimes (on the order of microseconds) and large Stokes shifts (above 100 nm), offering high potential for applications in bioimaging. The application of AuNCs is, however, hindered by their low colloidal stability and low photoluminescence quantum yield. To overcome these limitations, we studied the encapsulation of AuNCs, stabilized with either mercaptohexanoic acid (MHA-AuNCs) or hexanethiol (MH-AuNCs), into the hydrophobic core of hairy spherical polymer nanoparticles produced by aqueous RAFT-PISA at room temperature, using a photoinitiated process (Photo-RAFT-PISA). Our strategy successfully led to nanoparticles with a corona of poly(N-acryloyl morpholine) (PNAM) and a core of poly n-butyl acrylate (PnBA). Upon encapsulation, the AuNCs retained their photophysical properties and remained stable due to the low temperature used for polymerization. Our NIR-photoluminescent biocompatible polymer nanoparticles could be successfully imaged by confocal microscopy in cellulo. Finally, the versatility of the polymerization process allowed us to tune both the size and the surface chemistry of the NIR-emitting AuNCs–polymer hybrid nanoparticles.