A sandwich-type electrochemical biosensor was successfully constructed for the sensitive detection of pathogenic bacteria. In this biosensor platform, methylene blue (MB) organic–inorganic nanocomposites (MB@MI) were synthesized from magainin I (MI, antimicrobial peptide specific to Escherichia coli O157:H7), Cu3(PO4)2 and MB via a one-pot method, and were explored as a novel electrochemical signal label of biosensors generating amplified electrochemical signals by differential pulse voltammetry (DPV). E. coli O157:H7 specifically sandwich bound to the aptamers on the electrode surface and MB@MI nanocomposites, and the changes in the current signal generated on the electrode surface were used for the quantitative determination of E. coli O157:H7. Under optimum conditions, the proposed biosensor showed excellent performance with a wide linear range of 102–107 CFU mL−1 and a low detection limit of 32 CFU mL−1, featuring favorable selectivity, repeatability and stability. According to the experiments conducted on real samples, the proposed approach is capable of detecting pathogenic bacteria in clinical diagnostics.
