HKPerox-1 (1-20 μM; 24 h) is nontoxic to RAW264.7 macrophages[1]. HKPerox-1 (10 μM; 30 min) robustly visualizes endogenous H 2 O 2 production in macrophages in a selective manner[1]. HKPerox-1 should be co-incubated with 100 μM of trichloroacetonitrile (CCl3CN,) for H 2 O 2 detection and molecular imaging. DMSO should be avoided during H 2 O 2 detection, as DMSO could scavenge activated H 2 O 2 in the presence of CCl3CN . DMF is the recommended solvent to prepare probe stock solution.