Sol–gel derived carbon ceramic composite electrode containing a ruthenium complex for amperometric detection of insulin at physiological pH

Abstract

A novel modified ceramic carbon electrode (CCE) containing [Ru(bpy)(tpy)Cl]PF 6 complex was fabricated by the sol–gel technique. The reversible redox couple of Ru(II)/Ru(III) was investigated both as a solute in acetonitrile solution and as a component of a carbon-based conducting composite electrode. The electrochemical behavior and stability of the modified CCE were investigated by cyclic voltammetry. Peak currents for the Ru-doped CCE were controlled by diffusion from a limited field at lower scan rates and by semi-infinite diffusion at higher scan rates. Peak potentials and peak currents were not changed with the increase of pH in the range 3–10. The apparent electron transfer rate constant ( k s) and transfer coefficient ( α) were determined by cyclic voltammetry and they were about 29 s −1 and 0.63. The modified electrode showed excellent electrocatalytic activity toward insulin electro-oxidation in acidic solution and at physiological pH values. Insulin was determined chronoamperometrically at the surface of the modified electrode at pH 7. Under the optimized conditions, the calibration curve is linear in the concentration range 0.5 nM–0.85 μM. The detection limit (signal to noise is 3) and sensitivity are 0.4 nM and 7.602 A/M, respectively. The Ru complex-doped CCE shows good repeatability. The response time, t (90%) was short and equal to 0.3 s or less. The long-term stability was remarkable (6 months) and, especially the surface renewal repeatability by simple mechanical polishing (RSD for seven successive polishing is 1.3%). The advantages of the insulin amperometric detector based on the ruthenium complex doped CCE are high sensitivity, inherent stability at physiological pH, excellent catalytic activity for insulin oxidation and a less expensive and simple preparation in comparison with recently published methods.