The analytical properties of the immunosensors were evaluated by measuring RIgG using a competitive assay and alkaline phosphatase-labeled antibody. Amperometric measurements were performed using hydrogen peroxide as a substrate. For the first time, an optimization of the antigen-antibody ratio used in the assay was performed, which significantly reduced the immunological species used. An electrochemical immunosensor based on graphite-epoxy-RIgG was constructed, characterized, and optimized using EIS and CV techniques. Superior sensors were obtained with respect to analytical properties using these electrochemical techniques. The optimized immunosensors showed an enhanced analytical signal, better stability, and higher signal-to-noise ratio compared to the non-optimized ones. Although the sensitivity was reduced, the detection limit achieved was one order of magnitude lower. The optimized immunosensors also allowed the detection of lower RIgG concentrations (0.0069 µg/mL and 0.0014 µg/mL) compared to the standard composition of 20% graphite loading (not detectable) when GaRIgG-HRP concentration was 0.017% (v/v). Based on the results obtained in this work, future studies will focus on the development of immunosensors based on composites for determining human IgG at low concentrations for the diagnosis of diseases. Overall, this study provides valuable insights into the optimization of electrochemical immunosensors and their potential applications in the field of disease diagnosis.