An ultrasensitive mediator-free electrochemical detection method for proteins has been developed on an 8-sensors microfluidic platform. In this method, a sandwich immunoassay approach was used to detect prostate cancer biomarkers on screen-printed carbon electrodes. Fe₃O₄ nanoparticles with peroxidase like-activity were loaded onto graphene oxide nano-sheets resulting in a Fe₃O₄@GO composite with 1 µm average diameter as determined by dynamic light scattering and electron microscopy. Voltammetric studies and colorimetric assays confirmed the Fe3O4@GO composite material exhibited catalytic activity toward hydrogen peroxide reduction. Detection antibodies were covalently attached to Fe₃O₄@GO composite, the resulting biocomposite was used as a detection label in sandwich immunoassays for Prostate Specific Antigen (PSA) and Prostate Specific Membrane antigen (PSMA). The sensor surfaces of the array were coated with electrochemically reduced graphene oxide to improve conductivity and increase surface area, and then capture antibodies were attached through either adsorption or covalent binding to residual carboxylic groups on surface.  An optimized simple microfluidic system was used to deliver reagents to the electrode arrays and wash/remove unbound species. This sandwich assay based on catalytic reduction of hydrogen peroxide by Fe3O4@GO detection labels exhibited detection limits of 61 fg/mL for PSA and 9.8 fg /mL for PSMA.