Lanthanide-based luminescent probes for biological magnesium: accessing polyphosphate-bound Mg 2 .

Biomolecule-bound Mg 2+ species, particularly polyphosphate complexes, represent a large and dynamic fraction of the total cellular magnesium that is essential for cellular function but remains invisible to most indicators. Here we report a new family of Eu(III)-based indicators, the MagQEu family, functionalized with a 4-oxo-4 H -quinolizine-3-carboxylic acid metal recognition group/sensitization antenna for turn-on, luminescence-based detection of biologically relevant Mg 2+ species.