Bicomponent colorimetric probe based on carbon quantum dots and o-phenylenediamine for sensitive and selective Cu²⁺...

A bicomponent colorimetric probe based on carbon quantum dots (CQDs) and o-phenylenediamine (OPD) was established for the detection of Cu²⁺. Theoretically, light-generated electrons from CQDs were trapped by the dissolved oxygen, resulting in the production of superoxide radicals. The colorless OPD was oxidized by the superoxide radicals to its yellow oxidation product (OPD_ox). On the other hand, Cu²⁺ can bind onto the surface of CQDs and change the band gap of the CQDs. This change induces an inhibition of the photo-oxidation of OPD, thus resulting in a decrease of the absorbance of OPD_ox. The mechanism was demonstrated by a series of control experiments. The parameters influencing the sensing performance as well as potential interferences were investigated. Under the optimum conditions, a limit of detection of 30 nM was achieved. Moreover, this sensing system was applied to analyze Cu²⁺ in seawater and tapwater samples, and achieved satisfying results.