A digital microfluidic lab-on-a-chip for clinical diagnostic applications

The emerging paradigm of the lab-on-a-chip powered by microfluidics is expected to revolutionize miniaturization, automation and integration in the life science laboratory. However, the state-of-the-art microfluidic technologies, which are based on continuous-flow in etched microchannel, 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 inflexibility. In this thesis a nanoliter droplet-based microfluidic lab-on-a-chip, based on electrowetting actuation, is developed as an alternative to continuous-flow systems. The lab-on-a-chip is designed to perform fully integrated and automated assays on a human physiological sample. Individual components of the lab-on-a-chip are first designed and then integrated on the same monolithic chip for fully automated analysis of multiple samples. Biocompatibility of the electrowetting system is established by demonstrating repeatable and rapid transport of human physiological fluids such as whole blood, serum, plasma and saliva, and proteins such as boving serum albumin. Automated droplet formation from an on-chip reservoir is also shown for serum samples and enzymatic reagents. A colorimetric enzyme-kinetic assay (based on the Trinder's reaction) for glucose is developed and used as the model system to evaluate the applicability of the lab-on-a-chip for clinical assays. Glucose assays performed using standard solutions on the electrowetting chip compared well with results obtained using a reference method on a spectrophotometer. There is also no significant change in the activity of the enzymes under electrowetting conditions. In order to demonstrate the multiplexed operation of the lab-on-a-chip three assays were each done on 40, 80 and 120mg/dL glucose standards in fully integrated and automated fashion. The results were used to generate a calibration curve and also study the repeatability of the assays, which is a measure of droplet volume variability and cross contamination. Excellent reproducibility (CV < 3%) was seen in the assays indicating negligible cross contamination and excellent volume reproducibility. Glucose assays done on serum however did not compare well with reference methods and this is attributed to interferences which assume more significance while using lower sample to reagent mixing ratios. This work represents the first demonstration of fully integrated and automated operation of a digital microfluidic lab-on-a-chip in the nanoliter scale for biological assays on clinically relevant sample matrices. Future work involves implementing dilution strategies on-chip, developing more sensitive detection methodologies, and system integration issues such as assembly, packaging, and temperature control.