Abstract
A cell permeable fluorescence turn-on probe, AcGQCy7, was developed to image β-galactosidase activity in living cells. Once internalized by β-galactosidase-expressing cells, the probe was hydrolyzed into a highly fluorescent molecule, and the fluorescent signal was retained in mitochondria for several days. This resulted in a long-lasting and strong β-galactosidase-dependent intracellular fluorescent signal with little background fluorescence in the culture media.