Electrochemical and optical dual-mode detection of phenolic compounds using MnO2/GQD nanozyme

Phenolic compounds (PCs) have been widely employed in industrial activities and have also been found at threatening levels in natural environments, posing risks to human health and the environment. As a consequence, there is an increasing demand for the development of simple and sensitive detection methods of such pollutants. In this work, we report the use of manganese dioxide and graphene quantum dot (MnO2/GQD) composites as a dual-functional sensing platform for the electrochemical and colorimetric detection of catechol (CC) and dopamine (DA), two important PCs. Regarding the electrochemical detection, differential pulse voltammetry showed a linear relationship between current signal intensity and concentration of DA and CC over the linear ranges of 0.5-100 mu M and 5-150 mu M, with limits of detection of 0.05 mu M and 0.09 mu M for DA and CC, respec-tively. In addition, the composite was employed for the colorimetric detection of CC and DA through the oxidase mimic activity of the MnO2/GQD in the presence of 3,5,3,5-tetramethylbenzidine (TMB). Analysis in real samples showed that the MnO2/GQD composite can be used for the sensitive detection of CC and DA in river samples. The high surface area and improved electrochemical properties of the MnO2/GQD were demonstrated to be beneficial for dual sensing applications of phenolic compounds.