A reagentless and single-step electrochemical aptasensor with separation-free fashion and rapid response is developed for the Hg assay in dairy products. Herein, the sensing strategy is established on Hg-induced structural transition of the methylene-blue-tagged single-stranded DNA (ssDNA) from a flexible manner to rigid hairpin-shaped double-stranded DNA (dsDNA), generating an improved peak current for the Hg assay with a detection limit of 0.62 fM. Importantly, the best signal-to-noise ratio value can be obtained by exploiting Au flowers as sensing material and the optimal ssDNA concentration. The proposed sensor also exhibits high selectivity as a result of the specific thymine-Hg-thymine (T-Hg-T) coordination chemistry and can be applied to detect Hg in dairy products. With the use of the electric "signal-on" switch, the electrochemical aptasensor has the advantages of simplicity, ease of operation, and high sensitivity and specificity, offering a promising method to assess the safety of dairy products polluted with Hg.

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A MWCNT/Th/AuNP composite, used to construct an electrochemical biosensor for the mannose assay of living cancer cells, contained thionine as an electron mediator and simplified detection based on enzymatic catalysis for signal amplification.

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