A mononuclear nickel(II) complex as a redox mediator for electrochemical sensors

The mononuclear nickel bis oxamidato) complex $[(\mathbf{L})\mathbf{Ni}]^{2-};\mathbf{L}=o-\mathbf{phenylenebis}$ (N-ethyloxalamide) has a potential for use in electrochemical sensors. The $[(\mathbf{L})\mathbf{Ni}]^{2-}$ complex was characterized by, for example, UV-vis spectroscopy, and its redox properties were studied by cyclic voltammetry. $[(\mathbf{L})\mathbf{Ni}]^{2}$. shows a reversible redox event corresponding to the $\mathbf{Ni}^{\text{II}}/\text{Ni}^{\mathbf{III}}$ redox couple at $\boldsymbol{E}^{o^{\prime}}=360\ \mathbf{mV}(\Delta \boldsymbol{E}_{\mathrm{p}}=60\ \mathbf{mV})$. To study the electrochemical sensitivity a screen-printed carbon electrode (SPCE) was used and functionalized with [(L)Ni]2-. The modified electrode $[(\mathbf{L})\mathbf{Ni}]^{2-}$ @SPCE has been fabricated by drop-casting of $[(\mathbf{L})\mathbf{Ni}]^{2-}$ on the working electrode. The $[(\mathbf{L})\mathbf{Ni}]^{2}-{@}\mathbf{SPCE}$ electrode exhibits the characteristic of improved reversibility and enhances the current response of ferri/ferrocyanide redox couple compared to SPCE. Furthermore, the modified electrode shows a good electrocatalytic activity toward the oxidation of D-glucose and the reduction of nitrate, providing means as a new and promising electrochemical sensors material.