We　report　on　a　new　membrane-based　lateral-flow　assay　for　the　rapid　determination　of　the　algal　biotoxin　brevetoxin　B　(BrevTox)　that　can　be　found　in　fish.　Hollow　nanogold　microspheres　(HGMS)　with　an　average　size　of　45　nm　were　synthesized　by　using　the　reverse　micelle　method,　followed　by　functionalization　with　monoclonal　mouse　anti-BrevTox　antibody　(mAb-HGMS).　They　served　as　the　signalling　reagent.　Bovine　serum　albumin-BrevTox　conjugate　and　rabbit　anti-mouse　IgG　antibody　were　manually　spotted　on　the　nitrocellulose　membrane　and　served　as　reagents　for　the　test　line　and　control　line,　respectively.　Both　spherical　gold　nanoparticle-labeled　anti-BrevTox　antibody　(mAb-AuNP)　and　mAb-HGMS　conjugate　were　investigated　with　respect　to　their　suitability　as　signal-transduction　tags,　and　the　latter　was　found　to　give　improved　analytical　features.　The　HGMS-based　labeling　method　was　then　also　studied　in　terms　of　performance　in　the　immunodipstick　assay.　Under　optimal　conditions,　the　visual　detection　limit　(cut-off　value)　of　the　mAb-AuNP　based　assay　is　1.5　ng　mL-1,　while　the　sensitivity　of　the　mAb-HGMS　based　assay　is　as　low　as　0.1　ng　mL-1.　Yes/no　decisions　can　be　made　within　10　min　without　the　need　for　expensive　instrumentation.　The　results　for　the　analysis　of　target　BrevTox　in　spiked　fish　samples　showed　a　good　correlation　with　data　obtained　with　the　commercial　ELISA.　Importantly,　the　assay　gave　no　false　negative　results.　[Figure　not　available:　see　fulltext.]　©　2014　Springer-Verlag　Wien.