a hydrogen 
 peroxide ( h2o2)-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 h2o2 through release of the highly adhesive cell - penetrating peptide 
 and disruption of fluorescence resonance energy transfer . 
 the h2o2 sensor selectively reacts with endogenous h2o2 in cell culture to monitor the oxidative burst 
 of promyelocytes and in vivo to image lung inflammation . 
 targeting 
 h2o2 has potential applications in imaging and 
 therapy of diseases related to oxidative stress .