In　this　study,　a　novel　and　enzyme-free　electrochemical　immunoassay　was　developed　for　the　detection　of　alpha-fetoprotein　(AFP;　as　a　model　biomarker)　by　using　a　novel　redox　nanocatalyst,　patterned　gold-iridium　oxide　nanoparticle　assemblies　(Au-IrOx),　on　a　Prussian　blue　(PB)　functionalized　glassy　carbon　electrode.　The　as-prepared　Au-IrOx　nanospheres　were　not　only　used　for　the　labeling　of　secondary　anti-AFP　antibody　but　also　executed　for　water　oxidation.　With　a　sandwich　immunoassay　format,　the　electrochemical　measurement　was　carried　out　in　0.1　M　KNO3-HCl,　pH　3.2,　containing　1.0　mM　p-aminophenol　(AP).　Initially,　the　added　AP　was　oxidized　to　p-quinone　imine　(QI)　with　the　help　of　the　immobilized　PB　on　the　electrode,　and　then　the　generated　QI　was　reduced　back　to　AP　by　hydrogenation　reaction　from　water　oxidation.　The　self-produced　QI　reactants　were　catalytically　recycled　and　thus　amplified　the　signal　of　electrochemical　response.　Under　optimal　conditions,　the　electrochemical　immunosensor　displayed　a　wide　working　range　of　0.005　to　200　ng/mL　with　a　low　detection　limit　of　0.5　pg/mL　AFP　(at　3sB).　Intra-　and　inter-assay　coefficients　of　variation　were　below　10%.　In　addition,　the　methodology　was　validated　with　real　serum　samples,　receiving　a　good　agreement　with　the　results　obtained　from　commercially　available　electrochemiluminescence　automated　analyzer.　[Figure　not　available:　see　fulltext.]　©　2011　Springer-Verlag.