Fluorescence imaging of intracellular cadmium using a dual-excitation ratiometric chemosensor.

We described here a coumarin-based dual-excitation ratiometric probe for cadmium, CadMQ. This fluorescence sensor has high quantum yields of 0.59 and 0.70 in the metal-free and Cd2+-bound forms, respectively, and has a dissociation constant of 0.16 nM for Cd2+. CadMQ is cell permeable and locates within the acidic compartments of the cells. We further show that CadMQ is a useful tool to ratiometrically probe the change in the intracellular Cd2+ levels with the use of two excited wavelengths.