Glassy carbon electrode modified with electrodeposited cobalt oxide nanostructure shows an excellent electrocatalytic activity toward insulin oxidation at a wide pH range. Cyclic voltammetry, hydrodynamic amperometry, and flow injection analysis (FIA) were used for insulin determination at a picomolar and higher-concentration range. Amperometric determination of insulin at this modified electrode yielded a calibration curve with the following characteristics; linear range, 100 pM–15 nM; sensitivity of 83.9 nA nM−1 and detection limit 10 pM. FIA yielded the calibration curve with sensitivity and detection limit of 2.0 nA nM−1 and 25 pM, respectively. Furthermore, the RSD of repetitive FIA for 200 pM insulin (n = 13) is 2%. In addition, the interference effect of electroactive existing species (lactic acid, cholesterol, ascorbic acid, uric acid, and glucose) was eliminated by covering the surface of the modified electrode with nafion film. Fast response time, signal stability, high sensitivity, low cost, and ease of preparation are the advantages of the proposed insulin sensor.
