A lysosome-targetable fluorogenic probe, LysoFP-NO2, was designed and synthesized based on a naphthalimide fluorophore that can detect selectively carbon monoxide (CO) in HEPES buffer (pH 7.4, 37 °C) through the transformation of the nitro group into an amino-functionalized system in the presence of CO. LysoFP-NO2 triggered a “turn-on” fluorescence response to CO with a simultaneous increase of fluorescence