The McDevitt group has pioneered two core technologies. The first approach is a bead array described as the "electronic taste chip". Here digital fingerprints recorded at bead microreactors allow for the measurement and quantitation of solution dissolved analytes within complex fluids. The second approach, discovered recently, is a membrane microchip that has found utility in cellular analyses. Both the bead- and membrane-based microchips can be packaged within lab-card systems that have the footprint of a credit card. These biochip elements provide integrated microfluidics, sample delivery, on-board reagents, sample separation and analyte detection capabilities. The integrated components work together to create a test structure that can be utilized with little intervention by the user.

Microfluidics Infrastructure for Bead-Based Assays: We have developed nano-bio-chip structures, whereby complex assays are performed on chemically sensitized beads that are populated into etched silicon wafers with embedded fluid handling and optical detection capabilities. Immunoassays on the bead-array system are performed using ~280 um porous agarose beads, positioned in a micro-etched array of wells on a silicon wafer/chip platform. Each bead within the array is a self-contained microreactor system, with its selectivity determined by the specificity of the antibody that it hosts.

The bead-loaded nano-bio-chip is sandwiched between two optically transparent poly-methyl-methacrylate (PMMA) inserts, packaged within a metal casing, or "flow cell". This flow cell allows for delivery of sample and detecting reagents to the nano-bio-chip and the associated beads. In operation, fluids are delivered to the bead array via a top inlet. Unspent reagents are directed to a waste reservoir through a bottom drain outlet. The flow cell also allows visualization of signals generated, which are captured by a charge-coupled device (CCD) camera along with the use of transfer optics. Images of fluorescent (via epi-illumination) or colorimetric (via transmission mode) beads are captured with the CCD and analyzed to facilitate detection and, ultimately, quantitation of analytes in complex fluids.

Infrastructure for Cell-Based Assays: In addition to the bead-based sensor arrays, we have also developed miniaturized cell capture and analysis methodology. By replacing the microspheres with a membrane filter and modifying the microfluidics and digital image analysis capabilities, we have developed "cell processing units" that are suitable for a variety of important applications. Here, a mechanical entrapment strategy along with an optical measurement system, have been adapted to create efficient methods for detection of cells, bacteria and spores.

This novel approach has been employed in the context of online detection of bacillus spores in mail-handling facilities as well as for the enumeration of human CD4+ lymphocytes from whole blood samples. Initially, research-grade flow cell assemblies were created from 3-piece stainless steel cell holders consisting of a base, a support and a screw-on cap. Two circular poly-methylmethacrylate (PMMA) inserts house an etch track membrane. These two PMMA inserts have been drilled along their edge and one side to allow for passage of the fluid to and from the nano-bio-chip through stainless steel tubing. The bottom PMMA insert is modified in order to feature a drain and to contain a plastic screen disc that acts as a support for the filter element. The top insert also features an additional outlet, which can be used for the regeneration of the filter. Silicone tubing is fitted on the stainless steel tubing and, as such, is readily compatible with a wide range of fluidic accessories (i.e. pumps, valves, etc.) and solvents. Membranes with various pore sizes are used depending on the nature of the species of interest. For example, membranes with a 0.4 µm pore size are used to capture the 0.8 - 1.0 µm diameter spores, while membranes with a 3.0 µm pore size are used for whole blood analysis. These structures process one drop of whole blood and allow for the rapid isolation of the white blood cells from their much more numerous red blood cell counterparts. Likewise, the nano-bio-chip system allows lymphocytes and other white blood cells to be captured on the membrane, while enabling the more flexible red blood cells to flow through the pores of the fluidic structures. This feature of our system is a particular advantage because it does not require red blood cell lysis prior to analysis.