Fluorescent and Colorimetric Sensors Based on the Oxidation of o-Phenylenediamine

[Image: see text] o-Phenylenediamine (OPD) can be readily oxidized by several types of oxidants to generate fluorescent 2,3-diaminophenazine (oxidized OPD, OPDox). The unique fluorescence response process during the oxidation of OPD provides an important model for the design of novel sensors. In recent years, a series of fluorescent and colorimetric sensors have been developed based on the oxidation of OPD. In this review, fluorescent and colorimetric sensors for the detection of metal ions and small organic molecules are discussed. These sensing processes exhibit distinguishable and prominent fluorescent and colorimetric responses. The sensing systems include autocatalytic reactions and using nanomaterials, carbon dots, or fluorophore labeled DNA as reference fluorophore for fluorescent and colorimetric detection.