A hydrogen
peroxide (H<sub>2</sub>O<sub>2</sub>)-activated cell-penetrating
peptide was developed through incorporation of a boronic acid-containing
cleavable linker between polycationic cell-penetrating peptide and
polyanionic fragments. Fluorescence labeling of the two ends of the
molecule enabled monitoring its reaction with H<sub>2</sub>O<sub>2</sub> through release of the highly adhesive cell-penetrating peptide
and disruption of fluorescence resonance energy transfer. The H<sub>2</sub>O<sub>2</sub> sensor selectively reacts with endogenous H<sub>2</sub>O<sub>2</sub> in cell culture to monitor the oxidative burst
of promyelocytes and in vivo to image lung inflammation. Targeting
H<sub>2</sub>O<sub>2</sub> has potential applications in imaging and
therapy of diseases related to oxidative stress
