A　new　colorimetric　immunosensing　platform　accompanying　enzyme　cascade　amplification　strategy　was　fabricated　for　quantitative　screening　of　small-molecular　mycotoxins　(aflatoxin　B1,　AFB1　used　in　this　case)　coupling　with　enzyme-controlled　dissolution　of　MnO2　nanoflakes.　The　visual　colored　assay　was　executed　by　high-efficient　MnO2–3,3′,5,5′-tetramethylbenzidine　(TMB)　system　(blue).　In　the　presence　of　ascorbic　acid,　MnO2　nanoflakes　were　dissolved　into　Mn2+　ions,　thus　resulting　in　a　perceptible　color　change　from　blue　to　colorless.　The　reaction　could　be　weakened　through　ascorbate　oxidase　to　catalyze　ascorbic　acid　into　dehydroascorbic　acid,　which　indirectly　depended　on　the　concentration　of　ascorbate　oxidase.　By　using　ascorbate　oxidase/　anti-AFB1　antibody-labeled　gold　nanoparticles,　a　novel　competitive-type　colorimetric　enzyme　immunoassay　was　developed　for　detection　of　AFB1　on　AFB1-bovine　serum　albumin　(BSA)-conjugated　magnetic　beads.　Upon　addition　of　target　AFB1,　the　analyte　competed　with　the　conjugated　AFB1-BSA　on　the　magnetic　beads　for　the　labeled　anti-AFB1　antibody　on　the　gold　nanoparticles.　Under　optimal　conditions,　the　absorbance　decreased　with　increasing　target　AFB1　within　the　dynamic　range　of　0.05–150　ng　mL−1　with　a　detection　limit　of　6.5　pg　mL−1　at　the　3Sblank　level.　The　precision　and　specificity　of　the　MnO2–TMB-based　immunosensing　system　were　acceptable.　In　addition,　method　accuracy　was　further　validated　for　monitoring　spiked　peanut　samples,　giving　results　matched　well　with　those　obtained　from　commercialized　AFB1　ELISA　kit.　©　2015　Elsevier　B.V.