Luminescent organic–inorganic perovskite (CH₃NH₃PbBr₃) nanoparticles are used for the detection of 2,4,6-trinitrophenol (TNP, picric acid) in the solution and vapour state. Unlike most fluorescence based sensors, hybrid perovskite nanoparticles showed high selectivity and good sensitivity towards TNP, particularly in the solution state. Hydrogen bonding ability and electron accepting strength of TNP were found to play key roles in the detection mechanism.