Graphene Quantum Dots/l‑Cysteine Coreactant Electrochemiluminescence System and Its Application in Sensing Lead(II) Ions

A new coreactant electrochemiluminescence (ECL) system including single-layer graphene quantum dots (GQDs) and l-cysteine (l-Cys) was found to be able to produce strong cathodic ECL signal. The ECL signal of GQD/l-Cys coreactant system was revealed to be mainly dependent on some key factors, including the oxidation of l-Cys, the presence of dissolved oxygen and the reduction of GQDs. Then, a possible ECL mechanism was proposed for the coreactant ECL system. Furthermore, the ECL signal of the GQD/l-Cys system was observed to be quenched by lead­(II) ions (Pb2+). After optimization of some important experimental conditions, including concentrations of GQDs and l-Cys, potential scan rate, response time, and pH value, an ECL sensor was developed for the detection of Pb2+. The new methodology can offer a rapid, reliable, and selective detection of Pb2+ with a detection limit of 70 nM and a dynamic range from 100 nM to 10 μM.