Water and food contaminated with pathogens cause millions of hospitalizations and thousands of deaths, and costly recalls in food and retail industries annually. Among them, the Shiga Toxin-producing Escherichia coli (STEC) causes foodborne outbreaks every year, which leads to more than 265,000 illnesses, 3,600 hospitalizations, and 30 deaths in the United States alone. Currently approved detection methods, such as culturing and colony counting, or polymerase chain reaction (PCR), provide accurate diagnosis. However, these methods require long detection time (ranging from 6 to 24 hours), high testing cost, large-sized equipment, and/or skilled personnel, limiting their application in controlling outbreaks, reducing recall loss, or on-field diagnosis in developing countries. In this dissertation research, two biosensors were developed based on electrospun nanofiber and nuclear magnetic resonance (NMR) for rapid detection of STEC with high sensitivity. The electrospun biosensor was designed as lateral-flow immuno-sensor based on magnetic nanoparticles (MNPs) and electrospun nanofibers. The MNPs were coated with conductive nano-shells and functionalized with antibody to extract target pathogen by immunomagnetic separation. Biocompatible nanofibrous membrane was synthesized by electrospinning technique, which was optimized for nano-porous structure and excellent capillary properties. The electrospun membrane was functionalized with antibody to capture the MNP-pathogen conjugates by lateral-flow separation. As a result, the membrane’s conductivity was proportional to pathogen concentration, which could be measured by a portable impedance analyzer. Owing to the novel nanostructure, the surface area and mass transfer rate were significantly increased. This improved the biochemical binding effect and sensor signal to noise ratio. The biosensor’s sensitivity limit was 61 colony forming units per milliliter (CFU/mL) and 104 cell culture infective dose per milliliter (CCID/mL) for bacterial and viral samples, respectively, with detection time of 8 min. The electrospun biosensor has advantages of low cost and high sensitivity, which can be used for on-field biodefense and food safety applications. In the second work, a portable nuclear magnetic resonance (pNMR) biosensor was developed based on antibody functionalized MNPs as proximity biomarkers of the pathogen, which induced micro-magnetic variation to accelerate NMR resonance signal decay. The pNMR was designed using a hand-held magnet of 0.47 Tesla, a high-power radio frequency (RF) transmitter, and an ultra-low noise receiver capable of detecting 0.1 μV NMR signal. The pNMR biosensor assay and sensing mechanism was used in detecting E. coli O157:H7, and sensitivity limit was 76 CFU/mL in water samples and 92 CFU/mL in milk samples with detection time of 1 min. The pNMR biosensor is innovative for bacterial detection in food matrices and can be extended to other microbial or viral organisms by changing the antibody specificity. Besides, the pNMR biosensor can be used for on-field healthcare diagnostic and biodefense applications owing to its advantages of portability and speed of detection.
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