Near-Infrared-Luminescent Gold Nanoclusters Stabilized by End-Grafted Biocompatible Polymer Chains for Bioimaging

Goldnanoclusters (AuNCs) are an emerging class of nanomaterialsfor bioimaging, featuring high photostability, size-dependent luminescence,large Stokes shifts, long photoluminescence lifetimes, and good biocompatibility.However, when stabilized by small ligands, AuNCs exhibit a limitedcolloidal stability. Here, we report the synthesis of original "hairy"AuNCs with a diameter under 2 nm and NIR photoluminescence (for bothone-photon and two-photon excitation), stabilized by biocompatibleend-grafted poly(N-acryloyl morpholine) (PNAM) chainsprepared by RAFT polymerization. The AuNCs synthesis was carried outdirectly in water in the presence of thiol-terminated PNAM-SH chains.Compared with AuNCs stabilized by small ligands, our PNAM-AuNCs exhibitmuch better colloidal stability (unchanged for more than two months),a 2-fold increase in photoluminescence lifetimes, and significantlyenhanced quantum yields. Moreover, their properties could be successfullytuned using PNAM chains with molecular weights ranging from 3000 to11 000 g & BULL;mol(-1). These PNAM-AuNCs offeran excellent platform for the development of bioimaging probes withoutorganic dyes.