Electrochemical immunosensor of E. coli O157:H7 in food based on PPY-PANI and quantum dot microsphere conjugates

Abstract In this study, a sandwich immunosensor based on the conjugate of gold nanoparticles and quantum dot microspheres on polypyrrole/polyaniline (PPY-PANI) composite membrane was developed for the detection of Escherichia coli O157:H7 (E. coli O157:H7). Quantum dot microsphere conjugates (QBC), 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 ℃ and 60 min respectively, and the concentration of secondary antibody was 0.01 mg·mL− 1. When E. coli O157:H7 was performed in the immunosensor of PPY-PANI-Ab2, E. coli O157:H7 in the concentration range of 4.73×102-4.73×109 CFU·mL− 1, exhibited a linear relationship between the change of current (ΔIpa) and the logarithm of bacterial concentration. Compared to 100 CFU·mL− 1 of the limit of detection (LOD) in normal saline solution, the lowest detection limit in 0.1% peptone water was 113 CFU·mL− 1, 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 (RSD) was 3.03–6.18% and 1.61–6.94% respectively. Therefore, the immunosensor of with low cost and good stability is expected to be used for rapid screening of E. coli O157:H7 in food.