We　report　on　a　new　enzyme-free　electrochemical　immunoassay　for　the　sensitive　detection　of　the　p53　protein　(p53;　a　model　analyte)　by　using　a　screen-printed　carbon　electrode　modified　with　monoclonal　mouse　anti-human　p53　antibody　tagged　with　gold　nanoparticles.　First,　nanogold　microspheres　doped　with　Prussian　Blue　were　synthesized　by　a　reverse　micelle　method.　The　resulting　microspheres　were　used　to　label　polyclonal　anti-p53　antibody　which　then　was　applied　in　a　sandwich　immunoassay　in　pH　6.5　buffer　solution　using　the　Prussian　Blue　in　the　particles　as　the　redox-active　reporter.　The　electrochemical　signal　of　the　immunosensor　is　shown　to　increase　with　the　concentration　of　the　analyte　(p53　protein)　in　the　range　from　0.5　to　80　U　mL(-1),　with　a　detection　limit　of　0.1　U　mL(-1).　No　non-specific　adsorption　was　observed.　Coefficients　of　variation　for　intra-assay　and　inter-assay　were　below　8.5　%　and　11.5　%,　respectively.　In　addition,　the　method　was　applied　to　the　analysis　of　15　human　serum　samples,　and　a　good　relationship　was　found　between　the　new　immunoassay　and　the　referenced　electro-chemiluminescence　method.