A lysosomal-targeted fluorescent probe for detecting Cu2+

Copper in lysosomes is closely related to age and development of liver damage. A new fluorescent lysosomes-specific Cu2+-sensing probe was synthesized, and used for optical imaging in HL-7702 and HepG2 cells. Based on the difference in structure between spirocyclic (non-fluorescent) and open-cycle (fluorescent) forms, the probes showed an 80-fold fluorescence increase upon the addition of Cu2+. The probe showed excellent selectivity toward copper ion over other metal ions. A good linear correlation was obtained between fluorescent intensity and the concentrations of Cu2+ in the range from 1.0 × 10−7 to 5.5 × 10−6 M, with the detection limit as low as 80 nM. In particular, without appended targeting moieties, it can efficiently accumulate in lysosomes of normal liver and hepatoma cell lines, where it can specifically respond to Cu2+ level fluctuations in living cells, including adscititious and endogenous Cu2+ level decrease upon ascorbate-reduction, and it displayed good membrane-permeability and low cytotoxicity.