Au　nanoparticles　(AuNPs)　as　signal　reporters　have　been　utilized　in　colorimetric　in　vitro　diagnostics　(IVDs)　for　decades.　Nevertheless,　it　remains　a　grand　challenge　to　substantially　enhance　the　detection　sensitivity　of　AuNP-based　IVDs　as　confined　by　the　inherent　plasmonics　of　AuNPs.　In　this　work,　we　circumvent　this　confinement　by　developing　unique　dual-functional　AuNPs　that　were　engineered　by　coating　conventional　AuNPs　with　ultrathin　Pt　skins　of　sub-10　atomic　layers　(i.e.,　Au@Pt　NPs).　The　Au@Pt　NPs　retain　the　plasmonic　activity　of　initial　AuNPs　while　possessing　ultrahigh　catalytic　activity　enabled　by　Pt　skins.　Such　dual　functionalities,　plasmonics　and　catalysis,　offer　two　different　detection　alternatives:　one　produced　just　by　the　color　from　plasmonics　(low-sensitivity　mode)　and　the　second　more　sensitive　color　catalyzed　from　chromogenic　substrates　(high-sensitivity　mode),　achieving　an　＇on-demand＇　tuning　of　the　detection　performance.　Using　lateral　flow　assay　as　a　model　IVD　platform　and　conventional　AuNPs　as　a　benchmark,　we　demonstrate　that　the　Au@Pt　NPs　could　enhance　detection　sensitivity　by　2　orders　of　magnitude.　©　2017　American　Chemical　Society.