Europium-Infused Polystyrene Nanoparticles for Enhanced Bacterial Labeling in Microscopic Imaging

Luminescence microscopic imaging has become an indispensable tool in diagnostics and therapeutics. Lanthanide luminescent complexes (LLCs) have proven to be invaluable in this endeavor due to certain attractive characteristics such as long decay times, large Richardson shifts and narrow emission bands. However, the insolubility of these complexes and the negative effects of the aqueous environment on their photophysical properties still restrict their biological applications. By embedding luminescent Eu 3+ complexes into polystyrene nanoparticles (NPs), these complexes can not only maintain their photophysical properties, but even enhance them. This leads to exceptionally high quantum yields (> 90 %) and decay times ( >800 μ s). In addition, the surfaces of the NPs described here are covered with primary amine groups, which may be exploited for various interesting bioconjugation chemistries. In the present application, they were modified with N-hydroxysuccinimide (NHS) esters and then coupled either electrostatically or covalently to both, Gram-positive and Gram-negative bacteria, labeling them for luminescence microscopic imaging. This, to the best of our knowledge, is the first report of polymer NPs infused with LLCs for bacteria labeling. • Embedding europium in polystyrene NPs boosts quantum yields >90% and decay times >800 μs. • Amine-functionalized NPs enable versatile bioconjugation for biological use. • Functionalized NPs label gram-positive/negative bacteria for high-res luminescence imaging. • This method overcomes lanthanide solubility and photophysical limits in aqueous environments. • First use of polymer NPs with lanthanides for bacterial labeling demonstrated.