Developing enabling technologies for lab-on-a-chip applications by exploiting microscale fluid phenomena

In the past decade, microfluidics---the manipulation of fluid flow in micrometer-sized channels has emerged as a distinctive new discipline. The development of microfluidics is primarily fueled by the growing field of Lab-on-a-Chip which focuses on implementation of entire biological and chemical laboratory assays on a single microchip for applications such as lab miniaturization/automation and point-of-care diagnosis. The immediate advantage of reducing the size of fluidic systems to microscale is the dramatic reduction of sample consumption and instrument size. However it has been realized that the greatest potential of microfluidics lies in the microscale fluid physics itself. By exploiting the unique microscale fluid phenomena, precise manipulation of fluid flow, suspended particles/cells, and even light can be achieved in an unprecedented manner to facilitate the development of novel Lab-on-a-Chip applications. In this study we mainly focused on leveraging microscale fluid phenomena to develop enabling technologies for a wide variety of Lab-on-a-Chip applications. We first discussed a novel three-dimensional (3D) hydrodynamic focusing technique which can be implemented in a single-layer planar structure by utilizing a Dean flow based fluid manipulation technique---"microfluidic drifting." This simple yet extremely effective 3D hydrodynamic focusing technique has enabled us to develop a mass-producible, fully integrated, high-throughput, and multi-parametric flow cytometry chip for lab miniaturization and point-of-care diagnosis in resource-limited environment. In addition, we have further explored microscale fluid phenomena such as laminar flow, Dean flow, and diffusive mixing for the construction of a series of optofluidic tunable microlenses which can be used for flexible on-chip manipulation of light for various optics-based Lab-on-a-Chip applications. Lastly, we discussed the application of microbubbles induced chaotic advection in microscale fluid flow for ultrafast microfluidic mixing.