Synthesis and evaluation of the europiumIII and zincII complexes as luminescent bioprobes in high content cell-imaging analysis

Novel phenanthroline derivatives and their europium(III) and zinc(II) complexes have been prepared in up to 92%. In contrast to the stable zinc complexes, the europium compounds exhibit a strong luminescence in THF solution. However, quenching of the emission is observed in DMSO indicating complete dissociation of the complexes back to free ligands in this solvent. 1H NMR studies of the Eu(III)-complexes 5 and 6 also confirmed the existence of different states depending on the solvent used. Moreover, it was found that compound 5 is stable in EtOH–PBS solutions; here a strong signal in the emission spectra corresponding to the europium ion was detected. No spectral changes were observed for the zinc(II) complexes, they were shown to be stable in the media. These metal complexes can be used as fluorescence markers for the diagnosis of oesophageal squamous carcinoma (OE21) cells at low concentrations. Cell images were acquired using the compounds 5, 7–9 as luminescent agents. The first images were taken already after 20 min incubation time at a very low concentration range (0.7–1.6 μM).

Synthesis of novel europiumIII and zincII complexes has been developed. Photophysical evaluation and efficiency of the phenanthroline derivatives in the different media have been studied for development of stable luminescent bioprobes for high content intracellular analysis.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis of EuIII and ZnII phenathroline complexes was successfully developed.
► Photophysical studies were carried out to confirm their structure and stability.
► High content analysis has been performed on OE21 cell line.
► The concentration ranges have been defined for the series.