Ultrabright Fluorescent Polymeric Nanofibers and Coatings Based on Ionic Dye Insulation with Bulky Counterions

Preparation of bright fluorescent materials based on polymers is hampered by a fundamental problem of aggregation-caused quenching (ACQ) of encapsulated dyes. Here, ultrabright fluorescent polymeric nanofibers and coatings are prepared based on a concept of ionic dye insulation with bulky hydrophobic counterions that overcomes the ACQ problem. It is found that bulky hydrophobic counterion perfluorinated tetraphenylborate can boost >100-fold the fluorescence quantum yields of cationic dye octadecyl rhodamine B at high loading (30 wt %) in biocompatible poly(methyl methacrylate) (PMMA). The concept is applicable to both rhodamine and cyanine dyes, which results in bright fluorescent polymeric materials of four different colors spanning from blue to near-infrared. It allows for preparation of electrospun polymeric nanofibers with >50-fold higher dye loading by mass (30 wt %, >20-fold higher molarity for rhodamine dyes) while preserving good fluorescence quantum yields (31%), which implies drastic improvement in their fluorescence brightness. The counterion-based polymeric materials are also validated as coatings of model medical devices, such as stainless steel fiducials and 3D-printed stents of complex geometry. Spin-coated fluorescent polymeric films loaded with a dye paired with bulky counterions exhibit excellent biocompatibility and low toxicity. Moreover, counterion-modified materials show much better stability against dye leakage in the presence of living cells and a serum-containing medium, compared to materials based on the dye with a small inorganic anion. Overall, by pushing the barriers of ACQ, our counterion approach emerges as a powerful tool to develop ultrabright fluorescent polymeric materials ranging from nano- and macroscale.