Self-Assembly of Linear Polymers into Phosphorescent Nanoparticles: Optimization toward Non-Cytotoxic Bioimaging and Photonic Devices

Development of light-emitting polymers is usually hampered by inherent drawbacks such as photobleaching, stability, and functionalization issues. Formation of biocompatible, luminescent polymer particles often entails hazardous chemical cross-linking processes and/or doping with fluorophores susceptible to leaching and photobleaching. Here we describe the formation of size-tunable phosphorescent particles via self-assembly of chitosan and other linear polymers that bear positive surface charges upon polyelectrolytic complexation to a polyanionic gold(I) phosphor (AuP). The in situ self-assembly of phosphorescent chitosan nanoparticles is enabled by AuP that performs a quadruple role: a physical cross-linker, light emitter, sensor of polysaccharide rings with structures akin to those of some cancer markers, and contrast agent for electron microscopy. Size tunability in phosphorescent chitosan particles was achieved by systematic variations in pH or reactant concentrations. AuP exhibits “on–off” photoluminescence (PL) switching induced by several amine-bearing linear polymers, rendering the phosphorescent nanocomposites particularly attractive for biological imaging and sensing applications. Finally, combination of AuP-chitosan with a Pt-based orange-red phosphor leads to white-emitting thin films with high color-rendering index, remarkable stability, and PL quantum yields as high as 78% with <2% photobleaching. These properties render such thin films useful for applications in lighting and electronic displays.