A water-soluble, cell-permeable Mn(ii) sensor enables visualization of manganese dynamics in live mammalian cells.

Central roles of Mn ions in immunity, brain function, and photosynthesis necessitate probes for tracking this essential metal ion in living systems. However, developing a cell-permeable, fluorescent sensor for selective imaging of Mn ions in the aqueous cellular milieu has remained a challenge. This is because Mn is a weak binder to ligand-scaffolds and Mn ions quench fluorescent dyes leading to turn-off sensors that are not applicable for imaging.