Surface-Immobilized Core–Shell Polymer Nanoparticles as a Platform for Click-Mediated Attachments of Azide Dyes

Dual-emissive fluorescent surfaces based on fluorescent nanoparticles (FNPs) require precise control of surface chemistry and photophysical properties. Here, we report core–shell polymeric FNPs bearing a BODIPY core and a hydrophilic shell that enables both amide coupling and SPAAC click chemistry for surface functionalization. Four azide-functionalized dyes spanning different fluorophore families (coumarin─AF343, cyanine─Cy3, rhodamine─ROX, BODIPY─BDP-TR) were selected to evaluate Förster resonance energy transfer (FRET) with the FNPs. The photophysical properties of FNPs and Dye@FNPs were characterized in aqueous suspensions prior to grafting onto silica-based substrates functionalized by amino silane. These surfaces were characterized in depth at each step by XPS, ATR-FTIR, and AFM before reaction with the dyes via SPAAC. Steady-state measurements showed detectable ROX and BDP-TR emission on the resulting surfaces, while AF343 and Cy3 signals were limited. Time-resolved measurements revealed FNPs lifetime quenching upon grafting of Cy3, ROX, and BDP-TR, with BDP-TR providing the clearest evidence of FRET owing to its favorable spectral overlap and negligible emission overlap. These results establish SPAAC as a viable strategy for building Dye@FNPs surfaces across the visible spectrum and show that FNP-based FRET donor systems perform best with acceptors emitting in the orange-red range.