A Label-Free Electrochemical Immunosensor Modified with AuNPs for Quantitative Detection of Escherichia coli O157:H7

In this study, we used gold nanoparticles (AuNPs) modified screen-printed carbon electrodes (SPCE) with a large area working electrode for the detection of Escherichia coli O157:H7 ( E. coli O157:H7) in a direct method by antigen–antibody specificity binding. We compared four SPCE with different working electrode diameters (2 mm, 2.5 mm, 3 mm and 3.5 mm) to choose the optimum one. After electrodepositing chloroauric acid (HAuCl 4 ) on SPCE, a working electrode diameter of 3.5 mm SPCE show the maximum signal. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the electrochemical sensor. With the combination of large area working electrode and the great property of AuNPs, this immunoassay plays an ideal detection range from 1.19 × 10 3  CFU mL −1 to 1.19 × 10 9  CFU mL −1 and the limit of detection is 5.94 × 10 2 CFU mL −1 (equivalent to 3.5 CFU) at a signal-to-noise ratio of 3. The immunoassay showed the acceptable specificity, reproducibility, and stability for detection of E. coli O157:H7. These results indicate that this immunoassay has a promising application in the food safety industry.