A Bifunctional Nanocomposites Based Electrochemical Biosensor for In-field Detection of Pathogenic Bacteria in Food

This research focused on the application of electrochemical biosensors for the rapid detection of pathogenic bacteria, Escherichia coli O157:H7 and Salmonella Typhimurium, in foods. The possible presence of pathogenic bacteria in foods has always been a great threat to the wellbeing of people and the revenue of food companies. Therefore, the demand for rapid and sensitive methods to detect foodborne pathogens is growing. In this research, an impedimetric immunosensor was first developed for the rapid detection of E. coli O157:H7 and S. Typhimurium in foods. It was based on the techniques of immunomagnetic separation, enzyme labelling, and electrochemical impedance spectroscopy (EIS). This impedimetric immunosensor was capable of specifically detecting E. coli O157:H7 and S. Typhimurium within the range of 102 to 106 colony forming unit (cfu)/ml in the pure culture. The limits of detection (LODs) of E. coli O157:H7 in ground beef and S. Typhimurium in chicken carcass rinse water were 2.05 x 103 cfu/g and 1.04 x 103 cfu/ml, respectively. The second electrochemical biosensor was designed for rapid detection of E. coli O157:H7. This biosensor integrated magnetic GOx-polydopamine (PDA) based polymeric nanocomposites (PMNCs) which served dual functions as both the carrier and the label, and Prussian blue (PB) modified SP-IDMEs for measurement. The core-shell Abs/GOxext/gold nanoparticles (AuNPs)/magnetic beads (MBs)-GOx@PDA PMNCs acted efficiently to get a high load of enzyme onto the surface of bacterial cells. A filtration step separated the free PMNCs from the bonded ones and reduce the background noise to achieve better sensitivity. The constructed biosensor had been proved to be able to detect E. coli O157:H7 with the LOD of 52 cfu/ml in the pure culture. The third electrochemical aptasensor was developed to detect S. Typhimurium based on the concept of the bifunctional nanocomposites. The ssDNA aptamers were used as the biorecognition element. The achieved LOD in the pure culture was 96 cfu/ml. The biosensors developed in this research exhibited good specificity, reproducibility, and easy-to-operate, and are expected to find broad applications in the detection, especially in-field detection, of foodborne pathogens.