Organic Solvent and Surfactant Free Fluorescent Organic Nanoparticles by Laser Ablation of Aggregation-Induced Enhanced Emission Dyes

Less toxic and highly fluorescent nanoparticles are in high demand to image biological events and early-stage disease. A strategy to fabricate highly fluorescent organic nanoparticles by laser ablation of aggregation-induced enhanced emission (AIE) luminophores, which are free of any organic solvent and surfactant, is presented. As these dyes provide no concentration quenching, the increased number of photoluminescent molecules in a nanoparticle produces bright fluorescence even with their small size (<2 nm), making them highly suitable for intracellular uptake and imaging for a variety of biomedical applications. The design and synthesis of a new AIE luminophore, DCEtDCS, are reported and its photoluminescent quantum yield enhancement up to 58% in the aggregated state is demonstrated. Extremely stable nanoparticles of this luminophore with a narrow size distribution, by laser ablation in water are reported and its superior optical properties that are comparable to quantum dots are verified. The highly negative surface charge of these nanoparticles impedes cellular uptake, but when the surface is coated with chitosan, a cationic polymer, intracellular uptake in microglia is achieved. The strategy provides a novel tool to produce in water, ultrasmall and surfactant-free highly fluorescent organic nanoparticles suitable for biomedical applications.