Drop-based microfluidic technology has been attracting great attention since the prevalence of soft-lithography techniques in poly-dimethylsiloxane (PDMS) microfluidic device fabrication a decade ago. The miniaturized isolated confinement of the droplet provides an ideal environment to study single cell behaviors in vitro that might otherwise be buried in the ensemble measurements. The effective confinement of the target and its secretion, together with the high-throughput processing capability, holds the promise for efficient target search through large-scale library screening. In fact, in the past seven years, considerable efforts have been made in developing this platform towards the applications in biology and great advances in drops have been reported in areas such as directed evolution, DNA sequencing, drug screening, etc.;This thesis systematically describes our work that has been done in advancing the biological application of drop-based microfluidics through three major projects that are of significance in both fundamental research and clinical applications. Encapsulating in vitro transcription and translation reactions in the 0.5 pL drops enables us to synthesize a variety of functional RNAs and proteins from the single DNA templates in a drop environment, which not only provides a novel approach for single DNA molecule detection, but also paves the way for the high-throughput screening of the artificial proteins with drop-based microfluidics. Through successful enrichment of the restriction enzyme genes from a library consisting its truncated mutants, we demonstrated the high-throughput sorting capability of microfluidics for target gene screening that is beneficial for gene therapy applications. Finally, a non-invasive hydrogel synthesis method with microfluidic drop-maker and pico-injector is described, as a demonstration of microfluidic platform in the application of controllable synthesis of micro-sized gel particles as the 3D scaffold of, for example, mesenchymal stem cells, for the in vitro study of cell behaviors induced by cell-cell interactions and cell-environment interactions.
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