Immunoassay for foodborne pathogenic bacteria using magnetic composites Ab@FeO, signal composites Ap@PtNp, and thermometer readings.

A point-of-care (POC) immunoassay was established for the sensitive and rapid detection of pathogenic Escherichia coli O157:H7, using magnetic FeO organic-inorganic composites (Ab@FeO) for immunomagnetic separation, nanozyme platinum nanoparticle (PtNp) organic-inorganic composites (Ap@PtNp) for signal amplification, and thermometer readings. Antibodies and FeO were incubated in Cu phosphate buffer to synthesize the magnetic composite Ab@FeO with antibodies, to specifically capture E. coli O157:H7. Antimicrobial peptides and PtNp were incubated in Cu phosphate buffer to synthesize the signal composites Ap@PtNp with antimicrobial peptides (magainin I), recognizing and labeling E. coli O157:H7. In the presence of E. coli O157:H7, magnetic microcomposites targeted bacteria and signal microcomposites to form the sandwich structure: Ab@FeO-bacteria-Ap@PtNp for magnetic separation. Ap@PtNp of signal composites catalyzed HO to generate thermo-signals (temperature rise), which were determined by a thermometer. This point-of-care bioassay detected E. coli O157:H7 in the linear range of 10-10 CFU mL and with a detection limit of 14 CFU mL. One-pot process magnetic FeO organic-inorganic composites (Ab@FeO, magnetic microcomposites, MMC) for immunomagnetic separation and nanozyme platinum nanoparticle (PtNp) organic-inorganic composites (Ap@PtNp, signal microcomposites, SMC) were used as signal amplification and thermometer readings for E. coli O157:H7 detection.