Picomolar detection of insulin at renewable nickel powder-doped carbon composite electrode

A sol-gel technique was used for fabrication of a renewable carbon composite electrode (CCE) modified with nickel powder. This modified electrode shows excellent catalytic activity for the oxidation of insulin in alkaline solutions. The nickel powder was then oxidized to form a nickel oxide film electrode, which was used as an amperometric detector for hydrodynamic amperometry and flow injection analysis of insulin. It was found that the calibration curve was linear up to 30 microM with a detection limit of 40 pM under the optimized conditions for hydrodynamic amperometry using a rotating disk modified CCE. Flow injection amperometric determination of insulin at this modified electrode yielded a calibration curve with the following characteristics; linear dynamic range of 15-1000 pM, sensitivity of 8659.23 pA pM-1 cm-2, and detection limit of 2 pM. This electrode shows many advantages as an insulin sensor such as simple preparation method without using any specific electron-transfer mediator or specific reagent, high sensitivity, excellent catalytic activity, short response time, long-term stability, and remarkable antifouling property toward insulin and its oxidation product. Sensitivity, detection limit, and antifouling properties of this insulin sensor are better than all of the reports in the literature. Additionally, it is promising for monitoring insulin in chromatographic effluents.