Highly sensitive sensor for picomolar detection of insulin at physiological pH, using GC electrode modified with guanine and electrodeposited nickel oxide nanoparticles

The electrochemical behavior of insulin at glassy carbon (CC) electrode modified with nickel oxide nanoparricles and guanine was investigated. Cyclic voltammetry technique has been used for electrode-position of nickel oxide nanoparticles (NiOx) and immobilization of guanine on the surface GC electrode. In comparison to glassy carbon electrode modified with nickel oxide nanoparticles and bare CC electrode modified with adsorbed guanine, the guanine/nickel oxide nanoparticles/modified CC electrode exhibited excellent catalytic activity for the oxidation of insulin in physiological pH solutions at reduced overpotential. The modified electrode was applied for insulin detection using cyclic voltammetry or hydrodynamic amperometry techniques. It was found that the calibration curve was linear up to 4 mu M with a detection limit of 22 pM and sensitivity of 100.9 pA/pM under the optimized condition for hydrodynamic amperometry using a rotating disk modified electrode. In comparison to other electrochemical insulin sensors, this sensor shows many advantages such as simple preparation method without using any special electron transfer mediator or specific reagent, high sensitivity, excellent catalytic activity at physiological pH values, short response time, long-term stability and remarkable antifouling property toward insulin and its oxidation product. Additionally, it is promising for the monitoring of insulin in chromatographic effluents. (C) 2008 Published by Elsevier B.V.