Purpose: The objective of the present study was to develop a nanowell-based immunosensor using a screen printed interdigitated electrode (SPIE) for rapid and sensitive detection of E. coli O157:H7 in foods.
Methods: A nanoporous-gold-film (NGF) with a thickness of 120 nm and a pore size of ~20 nm was prepared by a metallic corrosion method. Then, the NGF was coated onto the gold surface of a SPIE through a self-assembled monolayer to form a nanowell-based electrode. Polyclonal antibodies against E. coli O157:H7 were immobilized on the electrode surface through covalent bonding. After a blocking solution was applied, a test sample was added. Target E. coli O157:H7 presented in the sample was captured by the immobilized antibody, resulting in a change in the impedance of the nanowell-based electrode surface.
Results: The results showed that the developed nanowell-based immunosensor was able to detect E. coli O157:H7 with an enhanced impedance signal when compared to an immunosensor without nanowell. The impedance value of the nanowell-based electrode was observed to increase a 10-fold for detection of E. coli O157:H7 in pure culture at a concentration of 105 CFU/ml in an applied volume of 45 µl. It was a label-free detection with a total detection time from adding the sample to obtain the final result within one hour. Further work will be concentrated on the optimization of conditions of the nanowell-based immunosensor, and detection of target bacteria in different foods.
Significance: The outcome of this study will improve the sensitivity of the immunosensor due to the greatly increased gold surface area with the help of nanowell-based electrodes, which will provide a sensitive, rapid and label-free method for detection of foodborne pathogens.