Electrochemical Immunosensor of Escherichia coli O157:H7 in Food based on PPY-PANI and Quantum Dot Microsphere Conjugates

In this study, a sandwich immunosensor based on the conjugate of gold nanoparticles and quantum dot microspheres on the polypyrrole/polyaniline (PPY-PANI) composite membrane was developed for the detection of Escherichia coli O157:H7. Quantum dot microsphere conjugates, as immunoprobes throughout electrochemical detection, exhibited signal amplifications. Each stage of the immunosensor preparation was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that the optimal reaction conditions of antigen and secondary antibody were 37°C and 60 min, and the concentration of secondary antibody was 0.01 mg/mL. When E. coli O157:H7 was performed in the immunosensor of PPY-PANI-Ab2, the cells in the concentration range of 4.73 × 102–4.73 × 109 CFU/mL exhibited a linear relationship between the change of current (ΔIpa) and the logarithm of bacterial concentration. The lowest detection limit in 0.1% peptone water was 113 CFU/mL, and the signal-to-noise ratio was 3. Moreover, the recovery rate of spiked milk and shrimp were 80.80–98.36 and 75.20–94.31%, and the relative standard deviation was 3.03–6.18 and 1.61–6.94%, respectively. Therefore, the immunosensor of with low cost and strong stability is expected to be used for rapid screening of E. coli O157:H7 in food.