We　designed　a　new　colorimetric　immunoassay　for　sensitive　monitoring　of　brevetoxin　B　(BTB)　using　enzyme-controlled　Fenton　reaction　with　a　high-resolution　3,3＇,5,5＇-tetramethylbenzidine　(TMB)-based　visual　colored　system.　Upon　addition　of　hydrogen　peroxide　(H2O2),　the　equivalent　iron(II)　could　be　first　converted　into　iron(III)　and　free　hydroxyl　radical　(•OH)　via　the　classical　Fenton　reaction.　Then　the　as-produced　iron(III)　and　•OH　could　cause　a　perceptible　change　from　colorless　to　blue　with　the　increasing　H2O2　concentration　in　the　presence　of　TMB.　Based　on　Fenton　reaction-triggered　visual　colored　system,　a　novel　competitive-type　colorimetric　enzyme　immunoassay　was　developed　for　the　quantitative　screening　of　target　BTB　on　the　bovine　serum　albumin-BTB-modified　magnetic　bead　using　glucose　oxidase/anti-BTB　antibody-labeled　gold　nanoparticle　as　the　signal-transduction　tag.　Upon　target　BTB　introduction,　the　analyte　competed　with　the　conjugated　BTB　on　the　magnetic　bead　for　anti-BTB　antibody　on　gold　nanoparticle.　The　carried　glucose　oxidase　with　the　gold　nanoparticle　could　implement　the　oxidation　of　glucose　to　produce　H2O2,　and　the　generated　H2O2　promoted　the　above-mentioned　Fenton　reaction　for　color　development.　Under　the　optimal　conditions,　the　absorbance　decreased　with　the　increasing　target　BTB　in　the　range　from　0.1　to　150　ng　kg-1　with　a　low　detection　limit　(LOD)　of　0.076　ng　kg-1.　The　LOD　was　500-fold　lower　than　that　of　commercialized　Abraxis　BTB　ELISA　kit.　Non-specific　adsorption　was　not　observed.　The　precision,　reproducibility　and　specificity　were　acceptable.　Finally,　the　method　accuracy　was　also　validated　for　monitoring　spiked　seafood　samples,　giving　results　well　matched　with　the　referenced　brevetoxin　ELISA　kit.　©　2016　Elsevier　B.V.