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Our long-term goal is to develop nanoporous silicon based sensor array on a microfluidic platform for simultaneous detection of multiple pathogens. Nanoporous silicon offers a novel nanoscale matrix for label-free molecular recognition through antigen-antibody binding. We will detect bacteria through sensing specific antigen-antibody interactions. An antibody will be immobilized on the inner surface of the nanopores. The penetration of the antigen into the pores, driven by specific binding to the antibody, will be observed as change in the interferometric reflectance spectrum. Immobilization of different antibodies at designated spots of nanoporous silicon will create a sensor array for multi-pathogen detection. Microfluidic platform that is responsible for processing and delivering bacterial cells will also be developed to interface the nanoscale biosensors with tiny amount of biological samples. We will also develop off-chip protocols that enable us to work with real samples of food safety relevance. We aim to fully assess the potential of nanoporous silicon based sensor arrays for bacteria detection. In the proposed research we will lay the ground work for applying this type of nanoscale biosensors to detect real biological samples. We will systematically study how the nanoscale structure affects the performance of the biosensor given a specific antigen-antibody pair.
NON-TECHNICAL SUMMARY: In the proposed research, we will develop sensor arrays based on nanoporous silicon for bacteria detection. We will systematically study how the nanoscale dimensions affect the biosensor\'s performance. We will design and implement a microchip platform needed by the nanoscale sensor array. To work toward real field applications in food safety industry, we will develop a prototype integrated chip system for biosensing based on bacterial cells separated from ground beef samples. Nanoporous silicon sensor array and lab-on-a-chip approach are the two key strategies in the proposed work to achieve high sensitivity and specificity together with rapid speed for bacteria detection. An integrated portable chip system proposed in this work will permit the usage in food factory labs for point-of-use analysis. Such local testing capacity will shorten the turnaround time for results and improve the ability for the food industry to handle emergencies and outbreaks.
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APPROACH: In the proposed study, our goal will be to develop a prototype chip-based sensor system which has nanoscale sensor array incorporated onto a microfluidic platform for bacteria detection. In principle, the device will be able to detect multiple pathogenic bacteria or molecules simultaneously given the availability of suitable immunoassays. We will demonstrate simultaneous detection of L. monocytogenes and two other molecular species (horseradish peroxidase and streptavidin) using the device with a limit of detection of ~20 cells for the bacterium. This LOD is not related to the initial sample volume. We expect that the device will be able to detect a bacterium with an initial concentration of 1 cell/mL or lower when proper off-chip concentration is performed. The detection will be based on immunoassays on nanoporous silicon surface on the chip device. The highly integrated chip will include two main components: the nanoporous silicon sensor array and the microfluidic platform for cell capture and lysis. Briefly, bacterial suspension after off-chip cleaning and concentration will flow into the chip and be filtered by a packed bed of microbeads and the bacterial cells will be retained in the bead array. The cells will then be lysed by applying electric pulses and intracellular materials (containing the target antigen) will be released to the downstream of the bead array where the nanoporous silicon sensor array is located. The reflective interferometric spectra will be taken at each spot of the array and the results will indicate the presence of target antigen(s).