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An electrochemical switching strategy is presented for the sensitive determination of Staphylococcus enterotoxin B (SEB). It is based on the use of DNA triangular pyramid frustum nanostructure (TPF) consisting of (a) three thiolated probes, (b) one auxiliary probe, and (c) an aptamer against SEB. The TPF was assembled on the gold electrode, with the SEB aptamer designed on top of the TPF. The electron transfer to hexacyanoferrate acting as an electrochemical probe is strongly inhibited in the TPF-modified electrode. This is assumed to be due to the formation of a 3D TPF structure that limits access of hexacyanoferrate to the electrode. Therefore, the Faradaic impedance is large. However, in the presence of SEB, it will bind to the aptamer and dehybridize the hybrid formed between aptamer and its complementary sequence. As a result, the TPF nanostructure changes to an equilateral triangle DNA nanostructure. This results in a more efficient electron transfer and a smaller Faradaic impedance. The method has a detection limit of 0.17 ng mL of SEB (at an S/N of 3) and a dynamic range that covers the 0.2-1000 ng mL concentration range. The applicability and reliability of the method was demonstrated by anayzing (spiked) milk samples, and the results were compared to those obtained with an ELISA kit. The relative standard deviations between the two methods range between -6.59 and 9.33%. Graphical abstract An electrochemical switching strategy is presented for the sensitive detection of Staphylococcus enterotoxin B based on 3D DNA structure conversion of nanostructure from triangular pyramid frustum to equilateral triangle.

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Specific primers were designed for Gadus morhua, Gadus chalcogrammus and Melanogrammus aeglefinus. Specificity of these specific primers was confirmed. Triplex HRM assay allowed easy and quick differentiation of the three species. G. morhua was detected in 30.8% (4/13) commercial codfish products. G. chalcogrammus was detected in 38.5% (5/13) commercial codfish products.