A　novel　signal-amplified　impedimetric　immunosensing　strategy　was　successfully　developed　for　ultrasensitive　detection　of　low-abundance　proteins　(carcinoembryonic　antigen,　CEA,　used　as　a　model)　based　on　hybridization　chain　reaction　(HCR)-stimulated　formation　of　DNAzyme　concatamers　on　nanogold　particle　accompanying　enzyme-triggered　biocatalytic　precipitation.　The　assay　was　carried　out　on　capture　antibody-modified　electrode　by　using　gold　nanoparticle　heavily　functionalized　with　initiator　strand　and　detection　antibody　as　the　signal-transduction　tag　with　a　sandwich-type　immunosensing　format.　In　the　presence　of　target　CEA,　the　formed　immunocomplex　underwent　an　unbiased　strand-displacement　reaction　by　the　initiator　strand　on　the　gold　nanoparticle　between　two　auxiliary　single-stranded　DNA　with　the　hemin　aptamer.　Upon　hemin　introduction,　numerous　DNAzyme　molecules　were　formed　on　the　concatamers　and　nanogold　particle,　which　could　catalyze　4-chloro-1-naphthol　to　produce　an　insoluble　precipitation　on　the　electrode,　thereby　resulting　in　the　amplification　of　impedimetric　signal.　Under　the　optimal　conditions,　the　immuno-HCR　assay　exhibited　good　impedimetric　responses　for　the　detection　of　target　CEA　in　the　working　range　from　1.0　pg　mL(-1)　to　20　ng　mL(-1)　with　a　detection　limit　of　0.42　pg　mL(-1).　In　addition,　the　immuno-HCR　assay　was　validated　by　measuring　six　human　serum　specimens　for　target　CEA,　receiving　a　highly　matched　correction　between　the　obtained　results　by　the　immuno-HCR　assay　and　the　commercialized　ELC-based　immunoassay　method.　(C)　2015　Elsevier　B.V.　All　rights　reserved.