Lanthanide?based bulky counterions against aggregation?caused quenching of dyes in fluorescent polymeric nanoparticles

Dye-loaded polymeric nanoparticles (NPs) are promising bioimaging agents because of their available surface chemistry, high brightness, and tunable optical properties. However, dye loadings can cause the aggregation-caused quenching (ACQ) encapsulated fluorophores. Previously, we proposed to mitigate ACQ inside NPs by insulating cationic dyes with bulky hydrophobic counterions. In order implement new functionalities into dye-loaded NPs, here, extend concept counterions anionic lanthanide-based complexes. We show that employing Gd-based octadecyl rhodamine B loaded at 30 wt% versus polymer, fluorescence quantum yield be increased 10-fold (to 0.34). Moreover, Gd-anion provides enhanced contrast in electron microscopy. A combination a luminescent Eu-based counterion far-red near-infrared cyanine 5 (DiD) yields Forster resonance energy transfer where UV-excited transfers DiD, generating delayed large stokes shift ?340 nm. Cellular studies reveal low cytotoxicity capacity internalize without detectable leakage, leaky small Our findings aggregation behavior controlled lanthanide anions, which will help developing bright multifunctional nanomaterials.