MEMS biosensor for detection of Escherichia coli O157:H7 in food products

Title from PDF of title page (University of Missouri--Columbia, viewed on May 24, 2012).The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file.Thesis advisor: Dr. Mahmoud AlmasriIncludes bibliographical references."July 2011"Escherichia coli O157:H7, is one of the most common pathogens that has caused several outbreaks in recent years. In 2010-11 there were 5 outbreaks of E.coli and thousands were victim of it. Thus there is an immediate need for sensors capable of rapid detection of this pathogenic strains of E.coli. To detect the presence of E.coli O157:H7 a MEMS based biosensor has been designed and fabricated. It 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 bacterium cells come in contact it binds to the antibody. This binding changes the dielectric property of the electrodes, resulting in an impedance change. This change is measured using an impedance analyzer. Another variation of this biosensor has been 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 dielectrophoresis is utilized to separate unwanted materials from the cells to increase the sensitivity of the biosensor. From the analysis it was found that the biosensor is sensitive to varying concentration of E.coli samples and the lowest detection limit of the biosensor is 3x103CFU/ml. Also it was established that the total detection time for this biosensor is less than 30 minutes which is rapid compared to the conventional ways of detection

Microelectromechanical systems impedance biosensor for accurate and rapid detection of Escherichia coli 0157:H7

Includes vita.Two Impedance biosensors based on interdigitated electrode (IDE) arrays were designed, fabricated and tested for detection of low concentration Escherichia coli O157:H7. The first biosensor consists of two set of gold IDE arrays embedded in a SU8-PDMS microchannel. Positive dielectrophoresis (p-DEP) is used to focus and concentrate the E.coli cells into the centre of the microchannel, using the first IDE array. The concentrated cells are then guided towards the sensing region microchannel, which has one-third the width of the initial microchannel. The bulk fluid keeps flowing toward the outer channel towards the waste outlets. The second IDE array located in the sensing region is used for impedimetric detection of the E.coli cells. A combination of standard photolithography, wet etching and plasma treatment techniques were used to fabricate the biosensor. The E.coli cells in the test solution were focused into the centre of the channel when excitation signal of 5 Vp-p at 5.6 MHz was applied across the electrode arrays. Before injecting the E.coli cells, polyclonal anti-E.coli antibodies were non-specifically immobilized on the sensing electrode array. This ensures specific detection of E.coli O157:H7 bacterial cells. As the concentrated E.coli cells (antigen) reach the sensing electrode array, they bind to the immobilized antibody sites. This antigen-antibody binding causes a change in the impedance which is measured using an impedance analyzer. The device performance was tested by measuring the impedance, between 100 Hz-1 MHz frequency, before and after applying p-DEP on the focusing electrode array, and after applying p-DEP on both the focusing and sensing electrodes. The result shows clearly that the use of p-DEP on the focusing IDE array significantly increased the measurement sensitivity with the lower detection limit being 3x10^2 CFU/mL. In addition, the use of p-DEP on both electrode arrays increased the measurement sensitivity by a factor of 2.9 to 4.5 times depending on the concentration. The second biosensor consists of a redesigned focusing region and multielectrode sensing region to improve the efficiency and to be able to detect even lower concentration E.coli O157:H7. Similar to the previous design this biosensor also consists of two functional region: focusing and sensing region. In this design, the focusing region consists a ramp down vertical electrode pair made of electroplated gold along with tilted (45 degree) thin film finger pairs, embedded in a microchannel. This configuration improves the concentration and focusing of the bacteria into the center of the microchannel, and direct them towards the sensing region. The sensing region consists of three IDE arrays, with varying number of electrode fingers (30, 20 and 10 pairs respectively), all embedded inside a narrow microchannel and functionalized using anti-E.coli antibody. As E.coli binds to the antibody, it results in impedance change. The biosensor was fabricated on a glass substrate using SU8 negative photoresist to form the microchannel, gold electroplating to form the vertical focusing electrode pair, thin gold film to form the detection electrode, the finger electrodes, traces and bonding pads, and PDMS to seal the device. This biosensor was able to detect concentrations as low as 39 CFU/mL, which indicates a 7.5 times higher sensitivity, over the previous design.Dr. Mahmoud Almasri, Dissertation Supervisor.|Includes vita.Includes bibliographical references (pages 91-99)

Efficient and Rapid Detection of Salmonella Using Microfluidic Impedance Based Sensing

We present a low cost, easy to fabricate biosensor, which can quickly and accurately detect Salmonella typhimurium. This study also compares the advantages of the microfluidic biosensor over a nonmicrofluidic biosensor. High density interdigitated electrode array was used to detect Salmonella cells inside a microfluidic chip. Monoclonal anti-Salmonella antibodies were allowed to be immobilized on the surface of the electrode array for selective detection of Salmonella typhimurium. An impedance analyzer was used to measure and record the response signal from the biosensor. The biosensor provides qualitative and quantitative results in 3 hours without any enrichment steps. The microfluidic biosensor’s lower detection limit was found to be 3×103 CFU/mL compared to the 3×104 CFU/mL of the nonmicrofluidic biosensor, which shows that the microfluidic biosensor has 10-fold increased sensitivity. The impedance response of microfluidic biosensor was also significantly higher (2 to 2.9 times) compared to the nonmicrofluidic biosensor