The　development　of　signal-amplified　colorimetric　immunoassay　relies　on　the　design　of　highly　efficient　signal-transduction　tags.　One　promising　route　is　to　exploit　a　novel　enzyme　mimetic　system　as　the　signal　label.　Herein,　we　report　that　urchin-like　(gold　core)@(platinum　shell)　nanohybrids　(Au@PtNHs)　can　be　utilized　as　a　highly　efficient　peroxidase　mimetic　system　for　in　situ　amplified　colorimetric　immunoassay　of　prostate-specific　antigen　(PSA,　one　kind　of　tumor　marker).　Initially,　urchin-like　Au@PtNHs　were　discovered　to　outperform　horseradish　peroxidase　(HRP)　by　a　vast　margin　in　terms　of　the　turnover　number　toward　hydrogen　peroxide　(H2O2)-3,3＇,5,5＇-tetramethylbenzidine　(TMB)　system　and　the　stability　against　high　temperatures　and　HRP　inhibitors.　Based　on　this　discovery,　the　assay　was　simply　carried　out　on　a　capture　antibody-immobilized　microplate　by　using　the　Au@PtNH-labeled　detection　antibody　as　a　signal-transduction　tag　with　a　sandwich-type　assay　mode.　The　colorimetric　signal　stemmed　from　the　labeled　Au@PtNHs　toward　catalytic　oxidation　of　TMB-H2O2　system.　Experimental　results　indicated　that　the　Au@PtNH-based　colorimetric　immunoassay　could　display　a　good　colorimetric　response　toward　PSA　in　the　dynamic　working　range　of　5-500pgmL-1　with　a　low　detection　limit　of　2.9pgmL-1.　Meanwhile,　the　developed　immunoassay　exhibited　good　precision　and　reproducibility,　high　specificity　and　acceptable　accuracy　for　the　detection　of　clinical　serum　samples.　These　results　open　up　a　new　horizon　for　the　development　of　highly　sensitive,　highly　stable　and　inexpensive　non-enzyme　immunoassay　platforms　as　an　alternative　to　conventional　enzyme-based　immunoassay　platforms.　©　2015　Elsevier　B.V.