Developing　simple,　high-efficiency　non-enzyme　bioassays　is　of　great　importance　for　modern　analytical　systems,　but　remains　a　significant　challenge.　One　promising　route　is　to　utilize　highly　efficient　nanocatalysts　with　the　exposure　of　active　crystal　facets.　Herein,　we　for　the　first　time　propose　a　novel　colorimetric　immunoassay　for　the　ultrasensitive　detection　of　the　human　prostate-specific　antigen　(PSA)　based　on　using　a　unique　type　of　nanolabel-high-index　{hk0}　faceted　platinum　concave　nanocubes　(HIF-Pt-CNCs).　The　proposed　HIF-Pt-CNCs　exhibit　superior　peroxidase-like　catalytic　activity　that　is　∼1500-　and　∼4-fold　higher　than　that　of　natural　horseradish　peroxidase　and　Pt　nanospheres,　respectively,　and　thereby　can　provide　powerful　signal　amplification　by　catalyzing　the　oxidation　of　peroxidase　substrates　in　the　presence　of　hydrogen　peroxide.　Using　the　HIF-Pt-CNC-labelled　anti-PSA　detection　antibody　as　a　signal　probe,　the　immunoassay　is　carried　out　in　anti-PSA　capture　antibody-immobilized　microplate　wells　in　a　sandwich-type　detection　mode.　Under　optimal　conditions,　the　developed　immunoassay　is　able　to　achieve　high　sensitivity　and　specificity　for　PSA　detection　in　a　linear　range　of　20-2000　pg　mL-1　and　with　an　ultralow　detection　limit　of　0.8　pg　mL-1,　which　is　much　lower　than　that　of　conventional　enzyme-linked　immunosorbent　assay　(ELISA).　Moreover,　the　method　is　validated　for　the　analysis　of　10　PSA　clinical　serum　specimens,　and　the　results　agree　very　well　with　those　obtained　by　using　a　commercialized　ELISA　kit.　Therefore,　this　new,　facile　and　efficient　immunoassay　is　a　promising　technique　with　potential　applications　in　medical　science　research　and　clinical　diagnosis.　This　journal　is　©　The　Royal　Society　of　Chemistry.