Simple modification of pencil lead electrode by graphenization and its application in insulin determination

Insulin is a very important polypeptide hormone which controls glucose level in blood and it is used for the treatment of insulin-dependent type I diabetes. So far, numerous sensitive methods have already been developed for the determination of insulin, such as bioassays [1], immunoassays [2] and high performance liquid chromatography [3]. These methods are time-consuming and slow and frequently require derivatizations of insulin with isotopes or fluorogenic labels to increase the sensitivity and selectivity. In recent years, electrochemical methods for insulin detection have been interested because of direct and rapid determination. Therefor several studies about in vitro electrochemical detection of insulin using modified common electrodes have been reported. In this study electrocatalytic oxidation of insulin was investigated on the graphenized pencil lead electrode (GPLE) surface. Graphenization process led to remarkable enhancement in sensitivity due to surface porosity. The influence of some experimental parameters such as: pH, scan rate, time and potential of graphenization were investigated. Under the optimum condition, linear range and the limit of detection with chronoamperometric method were obtained in the range of 0.5 -31.4×10-9 mol L−1 and 0.1×10-9 mol L−1, respectively. In addition, the modified electrode was successfully applied for analysis of blood serum as a real sample.