Visualizing changes in mitochondrial Mg during apoptosis with organelle-targeted triazole-based ratiometric fluorescent sensors.

Magnesium is one of the most abundant metals in cells and is essential for a wide range of cellular processes. Magnesium imbalance has been linked to a variety of diseases, but the scarcity of sensors suitable for detection of Mg with subcellular resolution has hampered the study of compartmentalization and mobilization of this ion in the context of physiological and pathological processes. We report herein a family of fluorescent probes for targeted detection of free Mg in specific intracellular organelles, and its application in the study of programmed cell death. The new sensors feature a triazole unit that plays both structural and electronic roles by serving as an attachment group for targeting moieties, and modulating a possible internal charge transfer process for ratiometric ion sensing. A probe decorated with an alkylphosphonium group was employed for the detection of mitochondrial Mg in live HeLa cells, providing the first direct observation of an increase in free Mg levels in this organelle in the early stages of Staurosporine-induced apoptosis.