Lab-on-a-Chip for Automated Immunoassays

Faculty Member: Dr. Srinivas Palanki
Graduate Student: Ramakrishna Sista

The emerging paradigm of the 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.

Although miniaturization was started in the early 1990s, there are no commercial devices that perform immunoassays involving magnetic beads. All the state-of-the art commercial microfluidic technologies, which are based on continuous flow in etched microchannels, have not been able to fully deliver the promised benefits of microfluidics. This is primarily due to their incompatibility with common sample matrices and architectural flexibility. Furthermore, the transport of the magnetic beads in microchannels is a difficult task in the continuous mode of operation as the magnetic susceptibility of the beads is rather weak and because of the demagnetization of the particles.

In this research, a droplet-based microfluidic lab-on-a-chip based on electrowetting actuation is developed to perform immunoassays using magnetic beads on human physiological samples. Biocompatibility of the electrowetting system is established by demonstrating repeatable and rapid transport of human physiological fluids such as whole blood, serum, other proteins such as bovine serum albumin, antibodies for insulin and interleukin-6 and enzymatic reagents such as horse radish peroxidase (HRP), alkaline phosphatase (ALP). Various magnetic configurations for efficient attraction of the magnetic beads which would assist in the washing are developed.

Several parameters involved in washing of the magnetic beads are studied and the buffer for resuspending the beads, optimum magnetic strength and optimum concentration of beads were established. An efficient protocol for washing of the magnetic beads on chip was developed with a bead retention efficiency of almost 100%. A complete magnetic immunoassay is performed on chip for Insulin and Interleukin-6 is performed. The least concentration of Insulin and IL-6 detectable on chip are 1.26 fg/mL and 0.07 fg/mL respectively. Standard curves are developed for both the analytes over a range of concentrations.

The repeatability (standard error-3%) of the assays is established by performing the assay on different samples on different days. Magnetic immunoassays are also demonstrated on serum for Insulin and IL-6. 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. Future work involves implementing on chip sample preparation, developing sensitive detection methodologies and system integration issues such as assembly and packaging.