Dual electrochemical determination of glucose and insulin using enzyme and ferrocene microcapsules

Dual electrochemical determination of glucose and insulin has been developed, based on enzymatic reaction and immunoassay with utilization of ferrocene microcapsules, respectively. Glucose was determined through electrochemical oxidation of formed product, hydrogen peroxide, by the action of glucose oxidase (GOx). The layer-by-layer (LbL) films on the ferrocene microcrystal followed by anti-insulin antibody sensitization were employed for the biolabled ferrocene microcapsules production. The antibody sensitized ferrocene microcapsules worked as a probe in the proposed system. The microcapsules provided a higher signal generating molecule to antibody (S/P) ratio of 4.52 × 106 to 12.4 × 106. Microcapsules with different antibody loads (388–1070 antibody molecules per capsule) were subjected to a solid-phase immunoassay for the detection of insulin. The microcapsule having 1030 anti-insulin antibody molecules per capsule demonstrated good performance for insulin determination. The calibration curve for insulin had a linear range of 10−10 to 10−7 g mL−1 with R2 = 0.990, 3.9% R.S.D. The limit of detection for insulin was 10 pg mL−1 of 100 μL sample (equivalent to 10−12 g of insulin). The determination range for the glucose was 0.5 and 40 mM with R2 = 0.996 and 4.1% R.S.D.