A　new　electrochemical　immunoassay　of　alpha-fetoprotein　(AFP)　was　developed　on　an　organic-inorganic　hybrid　nanostructure-functionalized　carbon　electrode　by　coupling　with　magnetic　bionanolabels.　Multi-walled　carbon　nanotubes　(CNTs),　single-stranded　DNA,　thionine　and　AFP　were　utilized　for　the　construction　of　the　immunosensor,　while　the　core-shell　Fe3O4-silver　nanocomposites　were　employed　for　the　label　of　horseradish　peroxidase-anti-AFP　conjugates　(HRP-anti-AFP-AgFe).　Electrochemical　measurement　toward　AFP　was　carried　out　by　using　magnetic　bionanolabels　as　traces　and　H2O2　as　enzyme　substrate　with　a　competitive-type　immunoassay　mode.　Experimental　results　indicated　that　the　immunosensors　with　carbon　nanotubes　and　DNA　exhibited　better　electrochemical　responses　than　those　of　without　carbon　nanotubes　or　DNA.　Under　optimal　conditions,　the　electrochemical　immunosensor　by　using　HRP-anti-AFP-AgFe　as　signal　antibodies　exhibited　a　linear　range　of　0.001-200　ng　mL(-1)　AFP　with　a　low　detection　limit　of　0.5　pg　mL(-1)　at　3S(B).　Both　intra-and　inter-assay　coefficients　of　variation　were　7.3%,　9.4%,　8.7%　and　10.2%,　7.8%,　9.4%　toward　0.01,　30,　120　ng　mL(-1)　AFP,　respectively.　The　specificity　and　stability　of　the　electrochemical　immunoassay　were　acceptable.　In　addition,　the　methodology　was　validated　for　12　clinical　serum　specimens　including　9　positive　specimens　and　3　normal　specimens,　receiving　a　good　correlation　with　the　results　obtained　from　the　referenced　electrochemiluminescence　assay.　(C)　2011　Elsevier　Inc.　All　rights　reserved.