Fig. 4. Ratiometric probes for quantitative analysis: (a) proposed sensing mechanism of DCM-βgal and BODIPY-βgal based on the ICT-induced process. Absorption (b) and emission spectra (c) of DCM-βgal with the presence of β-gal. Images of ratiometric (d) and light-up NIR fluorescence (e) of OVCAR-3 cells with or without the inhibitor of β-gal. (f) In vivo images of living mice treated with or without avidin-β-gal. (g) Three-dimensional mapping of β-gal in the mouse model.