“Fruity” Dye-based Fluorescent Nanoparticles (dFONs): A Fully Organic Counterpart of Alloy and Core-Shell Metallic Nanoparticles. Tuning Topology to Maximize Nano-interfacial Promoted Fluorescence Enhancement

Engineered nanomaterials are a blooming field of research among which luminescent nanoparticles are becoming major players for biological applications. While inorganic and hybrid organic-inorganic nanoparticles greatly dominate the field, research on all-organic nanoparticles is gaining momentum thanks to the versatility and tunability offered by advances in synthesis especially in polymer science but also by molecular engineering. Following this less travelled route, in the present work we demonstrate how to achieve ultra-bright dye-based Fluorescent Organic Nanoparticles (dFONs) mimicking metallic nanoparticles; i.e. core-shell and alloy type dFONs. Their design relies on the smart association of organic constituents that combine structural similarity, finely tuned electronic and photophysical properties for efficient Förster Resonance Energy Transfer if confined into close proximity. Strikingly, these nano-constructions show unique optical properties. First, both core-shell and alloy dFONs show highly efficient energy harvesting and giant absorption thanks to ultimate molecular confinement of a large number of strongly absorbing dyes. Second, we demonstrate for the first time that we can maximize the nano-interfacial emission enhancement (NIEE) effect by tuning the topology of core-shell type dFONs. Finally bioimaging experiments demonstrate that core-shell dFONs are internalized into COS7 cells and retain their specific emissive properties in these cells.