Fluorescence Lifetime-Resolved Ion-Selective Nanospheres for Simultaneous Imaging of Calcium Ion in Mitochondria and Lysosomes.

In this paper, novel calcium-selective nanospheres incorporating Pluronic F127 and (4-carboxybutyl) triphenylphosphonium bromide (TPP) as shell layers were designed to monitor the level of free calcium ion in mitochondria and lysosomes at living cells simultaneously. TPP as a target for mitochondria drove the nanospheres to bind intracellular mitochondria, while the lipophilic F127 layer resulted in the partial accumulation of nanospheres in lysosomes. This dual feature of the shell layer led to the colocation of nanospheres in both mitochondria and lysosomes. Chromoionophore III (ETH 5350) was chosen as the chromoionophore in the nanospheres that had different fluorescence lifetimes in either mitochondria or lysosomes, and therefore, the locations of the nanospheres at these two cellular compartments were identified. After the stimulation of cells using ionomycin, a burst of calcium concentration in mitochondria was observed that was associated with almost constant calcium concentration in lysosomes. The simultaneous recording of calcium ions in both of the compartments using fluorescence lifetime-solved nanospheres offered a special strategy to spatially monitor subcellular fluctuation of ions in living cells.