1-Azathioxanthone Appended Europium(III) Complexes with Excita-tion at 405 nm: Consequences for Lanthanide Luminescence based Bioimaging on Commercial Microscopes

Since the pioneering report by Selvin, we have been fascinated by the potential of using lanthanide lu-minescence in bioimaging. The uniquely narrow emission lines and long luminescence lifetimes both provide the potential for background free images together with full certainty of probe localization. General use of lanthanide based bioimaging was first challenged by low brightness, and later by the need of UV (<405 nm) excitation sources not present in commercial microscopes. Here, three lantha-nide-based imaging probes were synthesized, characterized, and used in bioimaging on dedicated as well as commercial microscopes. It was proven without doubt that the lanthanide complexes enter the cells and luminesce internally. Even so, no lanthanide luminescence were recovered on the commercial microscopes. Thus, it was concluded that even though the commercial microscopes are capable of single photon detection, lanthanide luminescence based bioimaging still requires dedicated hardware.