Electrochemiluminescence emission from carbon quantum dot-sulfite coreactant system

A new electrochemiluminescence (ECL) system consisting of carbon quantum dots (CQDs) and sulfite SO32- has been reported. In the ECL system, SO32- is a new ECL coreactant that can significantly enhance the cathodic ECL signal of CQDs. When cycling the potential between −1.300 and +1.400 V, SO32- is firstly electrochemically oxidized to sulfur trioxide anion free radical (SO3-) in the anodic polarization process. Then the electrogenerated SO3- is involved in a three-step auto-catalytic reaction in the presence of dissolved oxygen, producing sulfate radical (SO4-). In the subsequent cathodic polarization process, CQDs are electrochemically reduced to negatively charged CQDs (C−). Finally, the electrogenerated C− species react with the SO4- to form excited-state CQDs (C∗), emitting light (575 nm) when they come back to their ground states.