A “hydroxyl radicals standard” for evaluating the efficacy of anti-asthma drugs by using a two-photon NIR optical sensor

•The first two-photon NIR fluorescence probe was developed to detect ·OH.•We first found markedly elevated levels of ·OH in asthma via fluorescence imaging.•The “hydroxyl radical standard” was first introduced in asthma by using DCM-BOH.•This “standard” was used to evaluate the efficacy of co-administration in asthma.