LIQUID-CAPPED ENCODED MICROCAPSULE FOR MULTIPLEX ASSAYS

Abstract

In this dissertation, I introduce a new platform for the multiplex assays that enables the handling of thousands of different liquids in nanoliter volume. Handling tiny volume of liquids requires compartmentalization of precise volumes of the liquid, while preventing evaporation of the liquid in the air. Currently, the most representative method for handling small volume of the liquids is the droplet microfluidics, which compartmentalizes liquid droplets in immiscible oil phase to prevent the evaporation of the nanoliter volume of the liquid. The droplet microfluidics has been studied for more than a decade and the technology has now been applied in various biochemical applications such as drug screening, PCR enrichment for targeted sequencing and rare cell detection. Although its impact is already obvious in some applications, at present, the droplet microfluidics is used to analyze hundreds of thousands of aliquots of a single type of an analyte solution and there are few methods to process different analytes. Unlike common macroscale liquid carriers such as tubes and wells, which can be easily labeled to know their contents, the droplets are difficult to be labeled. To allow the droplet microfluidics with many different types of analytes, it would be necessary to label the droplets with a number of identification codes. In this dissertation, I solved this problem of labeling through the development of the encoded microcapsules. First, I developed the microfluidic device that enables to encapsulate nanoliter liquid inside the solid Teflon microcapsule. Teflon is chemically and biologically inert and highly flexible. These properties of the Teflon enable to encapsulate the liquid stably without evaporation and cross-contamination. I found that a photoinitiator mixed with the Teflon has photoluminescence property after the exposure to the UV light. Using this property, for the first time, I engraved graphical codes on the shell of the microcapsule to label the liquid held inside. This graphical code enables to handle numerous kinds of liquids and to make a pooled chemical library by mixing and storing the differently encoded microcapsules in a tube. For the multiplex assay with the encoded microcapsule, I also developed a microwell array platform that enables to assemble thousands of heterogeneous encoded microcapsules in the microwell array by a single pipetting process. The graphical codes on the microcapsules can be used to identify each liquid in the microcapsule even when they are randomly positioned in the microwells. To release the liquid inside the microcapsule, I also developed a laser releasing system for selective releasing and a mechanical releasing system for high-throughput releasing. To validate that the platform can be used for various liquid-liquid or liquid-cell reactions, I performed an enzyme inhibitor screening with the β-galactosidase, a virus transduction, and a drug-induced apoptosis test using osteosarcoma cells (U2OS) and anticancer drugs. The results including the dose-response curves and the corresponding IC50 values of the enzyme inhibitor screening and cell viabilities of the drug-induced apoptosis test showed good agreement with the results obtained using a conventional well-plate platform, confirming that the encoded microcapsule can be an efficient alternative liquid-format screening platform.