Supramolecular self-assembly of high-loaded horseradish peroxidase and biorecognized antibody into Au/polydopamine nanocomposites for sensitive immunoassay of E. coli O157:H7 in milk

It is an urgent need of rapid and sensitive method for detection of Escherichia coli O157:H7 (E. coli O157:H7), a class of hazardous foodborne pathogens in food safety. The traditional enzyme-linked immunosorbent assay (ELISA), a dominant rapid detection technic, takes disadvantages of low test sensitivity due to the insufficient enzyme loading capacity. In this study, we successfully synthesized the self-assembled Au/polydopamine (PDA)/HRP nanocomposites with the high enzyme loading on the outer surface and in the inner space. The high catalytic activity of Au/PDA/HRP was maintained by virtue of its hyperbranched flexible structure. For E. coli O157:H7 detection in milk samples, the proposed immunoassay achieved a visual cut-off value of 103 cfu mL-1 and a low limit of detection (LOD) of 2.8 × 102 cfu mL-1, 33 and 46 times more sensitive than the traditional ELISA, respectively. The tremendous advantages of high sensitivity, excellent specificity and adequate recovery make it promising for sensitively monitoring various kinds of pathogenic bacteria in food safety.