Fig. 1.

CIEEL energy transfer for imaging enzyme activities. a Chemical structures of 1,2-dioxetane chemiluminescent substrates and their activation by hydrolytic enzymes. Galacton-plus is a substrate for β-galatosidase, and CSPD is an alkaline phosphatase substrate. The hydrolytic activity of β-galatosidase or alkaline phosphatase removes the protective group X and results in substrate activation. b In the absence of a recipient fluorescent dye, the activated substrate self-decomposes and results in blue chemiluminescence emission or heat release due to water quenching. c In the presence of a fluorescent recipient, the activated substrate can directly transfer its chemical energy via formation of a charge-transfer complex with the recipient fluorophore