A　highly　sensitive　and　selective　impedimetric　immunosensor　with　triple　signal　amplification　was　designed　for　ultrasensitive　detection　of　prostate-specific　antigen　(PSA)　by　using　anti-PSA　antibody　and　DNAzyme-functionalized　gold-palladium　hybrid　nanotags　(Ab2-AuPd-DNA).　The　signal　was　amplified　based　on　the　Ab2-AuPd-DNA　toward　the　catalytic　precipitation　of　4-choloro-1-naphthol　(4-CN).　DNAzyme　(as　a　kind　of　peroxidase　mimic)　could　catalyze　the　oxidation　of　4-CN,　whilst　AuPd　hybrid　nanostructures　could　not　only　provide　a　large　surface　coverage　for　immobilization　of　biomolecules　but　also　promote　4-CN　oxidation　to　some　extent.　The　produced　insoluble　benzo-4-chlorohexadienone　via　4-CN　was　coated　on　the　electrode　surface,　and　hindered　the　electron　transfer　between　the　solution　and　the　electrode,　thereby　increasing　the　Faradaic　impedance　of　the　base　electrode.　Three　labeling　strategies　including　Ab2-AuNP,　Ab2-AuPd　and　Ab2-AuPd-DNA　were　investigated　for　determination　of　PSA,　and　improved　analytical　features　were　obtained　with　the　Ab2-AuPd-DNA　strategy.　Under　optimal　conditions,　the　dynamic　concentration　range　of　the　impedimetric　immunosensor　spanned　from　1.0pgmL-1　to　50ngmL-1　PSA　with　a　detection　limit　of　0.73pgmL-1.　Intra-　and　inter-assay　coefficients　of　variation　were　below　8.5%　and　9.5%,　respectively.　Importantly,　no　significant　differences　at　the　0.05　significance　level　were　encountered　in　the　analysis　of　6　clinical　serum　specimens　and　6　diluted　standards　between　the　impedimetric　immunosensor　and　the　commercialized　electrochemiluminescent　method　for　PSA　detection.　©　2013　Elsevier　B.V.