Reusable electrochemical biosensing platform based on egg yolk antibody-labeled magnetic covalent organic framework for on-site detection of Escherichia coli in foods

Escherichia coli O157:H7 (E. coli) can proliferate and contaminate foods rapidly to cause serious hazards to consumers. Thus, developing a rapid on-site detection assay for E. coli is urgent. We prepared an egg yolk antibody (IgY) with high specificity and affinity for E. coli from eggs laid by specific pathogen-free (SPF) hens immunized with inactivated E. coli. Meanwhile, novel magnetic covalent organic framework (m-COF) microbeads with large specific area and abundant porosity were made to label IgY as capture probes (m-COF@IgY) for efficiently enriching and recognizing E. coli. Ferrocene boronic acid (FBA) was used as a signal tag to conjugate E. coli with m-COF@IgY and form sandwich complexes that were magnetically separated and dropped on a screen-printed electrode to generate signals from FBA. Under optimal reaction conditions, the current intensity was proportional to the logarithm of E. coli concentration within the range of 10–108 CFU/mL, and the detection limit was 3 CFU/mL. The immunosensor was evaluated in food samples and demonstrated E. coli detection with high accuracy and speed (detection time ~20 min). The assay has great potential to be used as a point-of-care test of E. coli in foods.