A　new　sandwich-type　electrochemical　immunoassay　for　ultrasensitive　detection　of　staphylococcal　enterotoxin　B　(SEB)　in　food　was　developed　using　horseradish　peroxidase-nanosilica-doped　multiwalled　carbon　nanotubes　(HRPSiCNTs)　for　signal　amplification.　Rabbit　polyclonal　anti-SEB　antibodies　immobilized　on　the　screen-printed　carbon　electrode　(SPCE)　and　covalently　bound　to　the　HRPSiCNTs　were　used　as　capture　antibodies　and　detection　antibodies,　respectively.　In　the　presence　of　SEB　analyte,　the　sandwich-type　immunocomplex　could　be　formed　between　the　immobilized　anti-SEB　on　the　SPCE　and　anti-SEB-labeled　HRPSiCNTs,　and　the　carried　HRP　could　catalyze　the　electrochemical　reduction　of　H2O2　with　the　help　of　thionine.　The　high　content　of　HRP　in　the　HRPSiCNTs　could　greatly　amplify　the　electrochemical　signal.　Under　optimal　conditions,　the　reduction　current　increased　with　the　increase　of　SEB　in　the　sample,　and　exhibited　a　dynamic　range　of　0.05-15　ng/mL　with　a　low　detection　limit　(LOD)　of　10　pg/mL　SEB　(at　3s).　Intra-　and　interassay　coefficients　of　variation　were　below　10%.　In　addition,　the　assay　was　evaluated　with　SEB　spiked　samples　including　watermelon　juice,　soymilk,　apple　juice,　and　pork　food,　receiving　excellent　correlation　with　results　from　commercially　available　enzyme-linked　immunosorbent　assay　(ELISA).　©　2010　American　Chemical　Society.