MEMS impedance biosensor for accurate and rapid detection of E. coli O157:H7 in food products
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT REQUEST OF AUTHOR.] Escherichia coli O157:H7 is one of the public foodborne bacterial pathogens and results in severe illness such as diarrhea, urinary tract infections, respiratory illness, and pneumonia. To ensure food safety and human health, it is critical to develop rapid methods for E. coli O157:H7 detection. There were several outbreaks of E. coli O157:H7 pathogen in past years which endangered food safety and human health. The traditional bacterial culture testing method that are considered the gold standard, are time consuming (2-5 days) to confirm a diagnosis, and laborious. The PCR is faster but still requires 24 hours and overnight shipping. Thus, it is important to develop a rapid and effective detection method for this pathogen. In this study, a MEMS based biosensor has been designed, fabricated, and tested to effectively detect the presence of E.coli O157:H7 in food products. Impedance spectroscopy biosensor principal is utilized to detect E.coli bacteria. The biosensor consists of three regions for focusing, trapping, and detection of E.coli inside a microfluidic channel. the focusing region consists of a ramp down vertical wall along with tilted thin film fingers. This region focus and concentrate the bacteria cells into the center of the microchannel when dielectrophoresis (DEP) is applied and direct them toward the detection channel, while the bulk media are exited from the two sides toward the waste outlets. The detection region consists of three sets of interdigitated electrode array, each with ten pairs of fingers. The microchannel is infused with anti-E. coli antibody to modify the surface of the interdigitated microelectrode. As the E. coli bacteria sample is injected, it comes in contact with the modified interdigitated microelectrodes. The dielectric property of the interdigitated microelectrode changes as the E. coli bacteria cells bind to the E. coli antibody. Therefore, the impedance of the device changes and it can be measured using the impedance analyzer for the frequency range of 100 Hz-10 MHz. The biosensor device was designed with CAD (L-edit) tool and then fabricated using series of surface micromachining, SU-8 and PDMS processes on a glass slides. To study the sensitivity, and selectivity of the biosensor device, various E. coli samples were tested using impedance measurements. The results for each concentration were obtained by applying dielectrophoresis (DEP) effect on the focusing region, and without applying (DEP) effect. The results demonstrate that the device can detect as low bacteria concentrations as 13 cell/ml. The proposed biosensor device is selective and can detect other types of pathogen by changing the type of the antibody immobilized on the biosensor surface. The total detection time for the proposed biosensor is about 30 mins.
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