| Escherichia coli O157:H7, a gram-positive bacterium, is one of the most common pathogens and causes several E. coli infection outbreaks throughout the year. E. coli infection results in severe illness such as diarrhea, urinary tract infections, respiratory illness, pneumonia, etc. Every year in the United States, thousands of people fall victim to E. coli infection and many are hospitalized. In the last five years there have been at least 12 outbreaks of E. coli on various farms, ranches and dairies across the country. In 2010-11 there were 5 outbreaks of E. coli in food products such as beef, romaine lettuce, cheeses, hazelnuts and Lebanon bologna products. Thus there is an immediate need for sensors capable of rapid detection of pathogenic strains of E. coli in food products to reduce the amount of infection and outbreaks.;To effectively detect the presence of E. coli O157:H7 in food products a MEMS based biosensor has been designed and fabricated. This MEMS biosensor detects the E. coli bacteria based on the principal of impedance spectroscopy. The biosensor consists of planar interdigitated array of microelectrodes (IDAM) and a microchannel. The surface of the microelectrodes is modified using goat anti-E. coli polyclonal IgG antibody. As the E. coli sample is injected inside the biosensor through the microchannel, it comes in contact with the modified electrode surface. As soon as the E. coli bacterium cells get recognized by the anti-E. coli antibody it binds to the antibody. This binding changes the dielectric property of the electrodes, and as a result, the impedance of the device changes. The change in impedance is measured using an impedance analyzer which allows the study of the impedance response of the biosensor for a frequency range of 100 Hz - 1MHz.;Another variation of this biosensor has been designed and proposed in this thesis. This design consists of two arrays of 3-dimensional electrodes and a microchannel with multiple inlets and outlets. In this design the first array of interdigitated electrodes is used to separate unwanted objects from the sample using dielectrophoresis. The second array of 3-dimensional microelectrodes acts as a detection array and its surface is modified in similar fashion using anti-E. coli antibody. When the clean sample with E. coli cells reach the detection array, the bacteria cells get immobilized on the electrode surface causing a change in the dielectric property.;To investigate the sensitivity and selectivity of the biosensor, the impedance response is studied for various E. coli samples. From the analysis of the obtained response it was found that the lower detection limit of the biosensor is 3×103CFU/ml and it is sensitive to various concentrations of E. coli samples. This means the developed biosensor can detect as low as 3cells/µl. The biosensor was also tested for its selectivity and it was observed that it is only responsive to E. coli O157:H7 bacterium cells. The selectivity of the biosensor can be altered by changing the type of antibody immobilized on the sensor surface. Thus it can be used for detecting other types of pathogens too. The clinical detection time for E. coli bacteria using Colilert / Colitag methods (Enumeration) can take up to 24 hours. But the total detection time for this biosensor is about 30 minutes which is rapid compared to the conventional ways of detection. Also as the biosensor is small and portable, it can accommodate onsite testing, and owners of farms, dairies and ranches wouldn’t have to send their produce and/or meat products to a laboratory for sampling and pathogenic tests. All these features including optimal sensitivity, selectivity, fast response time and rapid detection ability give this biosensor great potential for industrial and societal benefit through implementation. |
