Electrochemical Detection of Gallic Acid-Capped Gold Nanoparticles Using a Multiwalled Carbon Nanotube-Reduced Graphene Oxide Nanocomposite Electrode

Recently, a plethora of ecofriendly methods have been developed for the synthesis of AuNPs using a multitude of biogenic agents. Polyphenols from plants are particularly attractive for producing AuNPs because in addition to helping with the synthesis of AuNPs, the polyphenol capping of the NPs can be used as a platform for versatile applications. Polyphenol-capped AuNPs could also make the detection of AuNPs possible, should they be released into the environment. Because polyphenols are redox-active, they can be used as a probe to detect AuNPs using electrochemical techniques. In this work, we have developed an MWCNT-rGO nanocomposite electrode for the sensitive detection of AuNPs capped with gallic acid (GA, a green-tea-derived polyphenol) using differential pulse voltammetry (DPV). The reduction of gallic acid-capped AuNPs was used as the quantification signal, and the calibration curve displayed a detection limit of 2.57 pM. Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), we have shown that the modification of the electrode surface with an MWCNT-rGO hybrid nanocomposite resulted in a 10-fold increase in current response leading to the sensitive detection of GA-AuNPs compared to unmodified electrodes. We have also demonstrated the applicability of the electrochemical sensor in detecting GA-AuNPs in various analytical matrixes such as human serum and natural creek water (Highland Creek, ON) with good recovery.