Prostate specific antigen (PSA) is an observable marker which is produced normally in men٫s blood. As a whole, the level of PSA in blood is 4 ng.mL-1. When the level of PSA in serum reaches more than 4 ng.mL-1, there is a high probability of prostate cancer [1]. Nowadays, due to the hopeful properties of electrochemical immunosensors such as fast analysis, sensitivity, low cost, specific and simple detection [2], they have been taken into consideration between others measuring methods. Noble metal nanoparticles, particularly gold nanoparticles (AuNPs) have been popularly used as electrochemical transducers for immunosensors owing to good biocompatibility, large efficient surface area, unique electrocatalytically properties and good electroconductibility [3-6]. Graphene oxide (GO) is one of the derivatives of graphene with two dimensional (2D) nanostructure single-atomic layered material with significant content of sp3 C-O bonds from oxygen in different group of carboxylic acid, epoxide and hydroxyl onto the surface has shown remarkable properties for utilizing in immunosensors [7,8]. Thus, in this respect we present a new immunosensor for detection of PSA tumor marker based on: First step, deposition of AuNPs onto the glassy carbon electrode surface, Second step, for completion of electrode surface, the special structure of rGO-AuNPs nanocomposite (rGO was decorated with AuNPs) was immobilized onto the surface electrode, Third step, 2 µl of 0.8 µg.mL-1 monoclonal PSA antibody (in 0.1 M PBS, pH 7.4) was added to the modified electrode (GC/AuNP/rGO-AuNP) via physisorption between amino groups of antibodies and AuNPs and covalent attachment between amino groups of antibodies and the COOH activated rGO. To block the free sites of GCE/AuNP/rGO-AuNP/PSA antibody, the modified electrode was immersed in 0.05 w/v% BSA solution for 1 h. Fig. 1 shows the cyclic voltammogram (CV) varies at each immobilization stage in 0.1 M KCl containing 5 mM Fe(CN)63- at scan rate 100 mV.s-1.
