Covalently dual functionalized graphene oxide-based multiplex electrochemical sensor for Hg(II) and Cr(VI) detection

In this work, a multiplex electrochemical sensor was fabricated by covalently functionalizing graphene oxide with thymine and carbohydrazide (Thymine-GO-Carbohydrazide, T-GO-C) via an epoxide ring cleavage, followed by a simultaneous-reduction approach. Multiplex electrochemical sensor constructed using T-GO-C poses excellent electrode stability and exhibits selectivity towards Hg(II) and Cr(VI) respectively observed at 0.27 V and 0.9 V vs Ag/AgCl reference electrode. The large surface area of graphene oxide coupled with good conductivity, and functionalization offers better selectivity towards Hg(II) and Cr(VI) over the other metal ions. The developed multiplex electrochemical sensor exhibit a linear range for Hg(II) and Cr(VI) in above 5 ppb. The minimum detection limits of Hg(II) and Cr(VI) were estimated to be 1 ppb and 20 ppb, respectively, which are well above their presence in the drinking water prescribed by the regulatory authorities such as WHO. The experiment was also performed with the screen printed electrodes, which could be used as a portable sensor or on-field detection of both Hg(II) and Cr(VI). These results indicates that the proposed sensor can show the way for the development of robust, high-performance multiplex sensing approaches for metal ion detection.