Peptides can serve as an ideal recognition elementfor many typesof cancer, as they offer high natural specificity toward the targetby mimicking endogenous substrate, so a peptide-based fluorescentprobe is an alternative approach for the detection of protein biomarkers.15,16 In our continuous efforts to employ peptides to construct probesfor imaging and regulation of proteins,17−20 we have overcome the dependenceon NADPH and O2 for HO-1 detection by reporting a peptide-basedfluorescent probe NBD-P5 that acts independently of thecatalytic ability of HO-1. The gene discussed is HMOX1; the disease is cancer.