A facile and sensitive ratiometric fluorescent sensor for determination of gallic acid

Gallic acid (GA), which is widely found in some tea leaves, fruits and medicinal materials, has a variety of biological activities, including anti-oxidation, anti-cancer, anti-bacterial. Thus, monitoring the amount of GA is of great significance. We developed a GA ratiometric fluorescent sensor by carbon dots (CDs), CoOOH nanoflakes and o-phenylenediamine (OPD). In the absence of GA, OPD can be oxidized to 2,3-diaminophenazine (DAP) by CoOOH nanoflakes. DAP not only quenches the fluorescence of CDs at 450 nm through the inner filter effect (IFE), but also produces a new fluorescence emission peak at 570 nm. However, the presence of GA is able to cause collapse of CoOOH nanoflakes which are reduced to Co 2+ , thus impeding the formation of DAP. Based on this principle, ratiometric detection of GA is achieved. The novel ratiometric fluorescent sensor shows high sensitivity toward GA and the linear response is observed in the 2.0–60.0 μmol L −1 with a detection limit of 1.2 μmol L −1 . Furthermore, the CDs/CoOOH nanoflakes/OPD sensor is applied to the detection of GA in green tea.