(617f) Development of a Digital Microfluidic Lab-on-a-Chip for Automated Immunoassay with Magnetically Responsive Beads

The emerging paradigm of lab-on-a-chip powered by microfluidics is expected to revolutionize miniaturization, automation and integration in the point-of-care centers which require quick, efficient and reproducible results. Furthermore, high throughput requirement from the life sciences laboratories have made the development of lab-on-a-chip a major area of research over the past few years. Immunoassays, which are routinely used to determine the concentrations of various analytes in life sciences laboratories, are one of the most important laboratory tests that require efficient automation and integration. The immunoassays also involve the application of magnetically responsive beads to increase the surface area for the reactions thereby enhance the signal. In this research, a droplet-based microfluidic lab-on-a-chip based on electrowetting actuation is developed to perform immunoassays using magnetic beads on clinical relevant antigens. Biocompatibility of the electrowetting system is established by demonstrating repeatable and rapid transport of human physiological fluids such as whole blood, serum, proteins such as bovine serum albumin, antibodies for insulin and interleukin-6 and enzymatic reagents such as horseradish peroxidase (HRP), alkaline phosphatase (ALP). Efficient washing of magnetic beads is a critical operation for performance of immunoassays on the chip and this abstract presents characterization of all the parameters that affect washing of magnetic beads in a droplet format. Various magnetic configurations such as position of magnet pull force and field strength are characterized for efficient attraction of the magnetic beads that in turn assist in efficient washing. Other parameters such as buffer for resuspending the beads and concentration of beads were also established. An efficient protocol for washing magnetic beads on chip was developed with a bead retention efficiency of almost 99.99995% after 3125 fold dilution-based washing. Using the washing strategies developed, a completely automated magnetic immunoassay is performed on chip on Insulin and Interleukin-6 (IL-6). Using a chemiluminescent substrate, the limit of detection of Insulin and IL-6 on chip is 0.24 pg/μL and 4 fg/μL respectively. Standard curves are developed for both the analytes over a range of concentrations. The repeatability of the assays is established by performing the assay on different samples on different days and the standard error is determined to be less than 3%. Magnetic immunoassays on the droplet based lab-on-a-chip are also performed on serum for Insulin and IL-6 and it is shown that the results are comparable to data obtained via conventional laboratory analysis. This work represents the first demonstration of integrated and automated operation of a digital-microfluidic lab-on-a-chip for immunoassays involving magnetically responsive beads on clinically relevant sample matrices.