"The technology can significantly benefit the food industry by enhancing the laboratory-testing capabilities of food manufacturers and food testing laboratories as well as field-testing activities of governmental agencies."

Rapid, quantitative, and reusable immunosensors for bacteria detection on a microfluidic platform

Investigator: Chang Lu (Department of Agricultural and Biological Engineering)

Project Report 2008 - 2009

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Project Rationale

Portable, rapid, and sensitive biosensors for food safety applications enable point-of-care contamination detection and immediate interpretation of the results. In our research project, we proposed to develop an integrated biosensor system on a microfluidic chip for detecting bacteria based on immunoassays. The device will offer a detection sensitivity of 102 to 103 bacteria cells and an assay time of fewer than 20 minutes for a single test. Our system will yield quantitative data for estimating the number of the target bacterium in a food sample. The microfluidic system will consist of individual devices for cell lysis, lysate purification, and immunoassays. In principle, the tool will be effective for any bacterium or strain given the availability of a suitable intracellular antigen-antibody pair. In this project, we will demonstrate the concept using an intracellular antigen, alcohol acetaldehyde dehydrogenase (Aad), and its monodonal antibody (MAb-H7) to detect Listeria monocytogenes. In order to concentrate L. monocytogenes cells from food samples, we will fabricate magnetic nanobars with different sizes and geometries and develop protocols for immobilizing antibodies specific to L. monocytogenes on the surface.

A portable, reusable, and low-cost device would be useful for point-of-care analysis in the food manufacturing industry. Conducting bacteria detection tests within food manufacturing laboratories would dramatically decrease the turnaround time for the results and avoid potential contamination and changes in the bacteria during transit. Conventional analytical methods require bulky, expensive equipment that is often cost-prohibitive for food manufacturing laboratories. With our lab-on-a-chip approach, sophisticated functions of a biological laboratory can be miniaturized on a microchip, enabling any minimally equipped laboratory to perform bacteria detection tests. The technology can significantly benefit the food industry by enhancing the laboratory-testing capabilities of food manufacturers and food testing laboratories as well as field-testing activities of governmental agencies.

Project Objectives

  • Fabricate magnetic nanobars with different sizes and geometries and develop protocols for immobilizing antibodies specific to L. monocytogenes on the surface. The amount of bacterial cells bound to the surface will be characterized under different conditions.
  • Develop an electrophoresis-based immunoassay coupled with laser-induced fluorescence on a microfluidic chip. We will use this tool to quantitatively detect L. monocytogenes based on cell lysate via the interaction between Aad and MAb-H7.
  • Demonstrate a prototype integrated microfluidic system which incorporates different steps such as manipulation of magnetic nanobars, cell lysis, lysate purification, and immunoassay.

Project Highlights

We have been developing an on-chip immunoassay that detects an intracellular antigen of L. monocytogenes (Aad) based on polystyrene beads functionalized with Aad antibody. We manipulated these beads in the microfluidic channel so that they were mixed thoroughly with the cell lysate. After binding with the antigen in the lysate, the beads were exposed to fluorescently labeled Aad. The detected bacterial concentration was inversely proportional to the fluorescence intensity from the beads after washing. Our detection method and device will be useful generally for immunoassays based on cell lysate. Such an approach will be important for developing portable microchip sensors for food safety applications.