Scheme 1.

Schematic representation of the simultaneous detection of pathogenic bacteria by the proposed electrochemical biosensor using E. coli O157:H7 and Vibrio cholerae O1 as a model: A, Schematic diagram of the simultaneous electrochemical system; B, Preparation of the bioconjugates- and nanoparticles-labeled antibodies; C, Schematic diagram of the immunoassay on magnetic beads. Abbreviations: Ab(O157) or Ab(O1), antibodies for E. coli O157:H7 or Vibrio cholerae O1; Bio-Ab, biotinylated antibodies; H1-4, hairpin nucleotide for HCR reaction; MB@SA, streptavidin-coated magnetic beads; NI1-2, nucleotide initiator; SP1-2, signal probe. (The schematic diagram is helpful for understanding the fabrication of the electrochemical assay, but it is not in proportion).