Colorimetric　sensing　methods　based　on　non-spherically　symmetric　gold　(Au)　nanoparticles　have　become　a　powerful　tool　in　the　field　of　biomedical　detection　due　to　their　intriguing　plasmonic　properties.　In　this　study,　Au　nanobipyramids　(Au　NBPs)　were　used　as　colorimetric　sensing　probes　to　detect　ferrous　ions　(Fe2+)　through　tip　etching.　The　quick　etching　of　Au　NBPs　along　the　longitudinal　direction　by　superoxide　radicals　generated　by　the　reaction　of　Fe2+　and　H2O2　led　local　surface　plasmon　resonance　(LSPR)　to　blue　shift　and　produced　vivid　color　change　that　could　be　used　for　visual　inspection.　Under　the　optimal　reaction　conditions,　the　peak　shift　of　the　Au　NBPs　and　the　logarithm　of　the　concentrations　of　Fe2+　had　a　linear　relationship　in　the　range　of　10　nM　to　10　μM,　with　a　very　low　detection　limit　of　1.29　nM.　During　the　etching　process,　a　different　end　shape　of　the　Au　nanoparticles　results　in　a　different　process　for　the　morphology　transition,　which　makes　the　degree　of　spectral　change　and　detection　sensitivity　significantly　different.　In　the　presence　of　trace　amounts　of　Fe2+　(　©　2020　IOP　Publishing　Ltd.