A　new　impedimetric　immunoassay　protocol　based　on　enzyme-triggered　formation　of　tyramine-enzyme　repeats　on　gold　nanoparticle　(AuNP)　was　designed　for　highly　sensitive　detection　of　carcinoembryonic　antigen　(CEA,　as　a　model)　by　virtue　of　utilizing　enzymatic　biocatalytic　precipitation　toward　4-chloro-1-naphthol　(4-CN)　on　anti-CEA　antibody　(Ab1)-modified　immunosensor.　Initially,　AuNP　was　functionalized　with　horseradish　peroxidase　and　detection　antibody　(HRP-AuNP-Ab2),　and　then　HRP-tyramine　conjugate　was　utilized　for　the　formation　of　tyramine-HRP　repeats　through　the　triggering　of　the　immobilized　HRP　on　the　AuNP　with　the　aid　of　H2O2.　In　the　presence　of　target　CEA,　the　carried　HRP-tyramine　repeats　accompanying　the　sandwiched　immunocomplex　catalyzed　the　4-CN　oxidation　to　produce　an　insoluble　precipitation　on　the　immunosensor,　thus　causing　a　local　alteration　of　the　conductivity.　Three　signal-transduction　tags　including　HRP-Ab2,　HRP-AuNP-Ab2,　and　HRP-AuNP-Ab2　with　HRP-tyramine　repeats　were　employed　for　target　CEA　evaluation,　and　improved　analytical　properties　were　achieved　by　HRP-AuNP-Ab2　with　HRP-tyramine　repeats.　Using　the　unique　signal-transduction　tag,　the　analytical　performance　of　the　impedimetric　immunoassay　was　studied　in　detail.　Under　the　optimal　conditions,　the　impedimetric　immunosensor　displayed　a　wide　dynamic　working　range　of　between　0.5　pg　mL-1　and　40　ng　mL-1　with　a　detection　limit　(LOD)　of　0.38　pg　mL-1　relative　to　target　CEA.　The　coefficients　of　variation　(CVs)　were　≤9.3%　and　13.3%　for　the　intra-assay　and　interassay,　respectively.　The　levels　of　CEA　in　eight　clinical　serum　specimens　were　measured　by　using　the　developed　impedimetric　immunosensor.　The　obtained　results　correlated　well　with　those　from　the　electrochemiluminescent　(ECL)-based　immunoassay　with　a　correlation　coefficient　of　0.998.　©　2014　American　Chemical　Society.