Document Type



Doctor of Philosophy


Materials Science and Engineering

First Adviser

Cheng, Xuanhong

Other advisers/committee members

Gilchrist, James; Oztekin, Alparslan; Rickman, Jeffrey M.


Focusing and separation of bionanoparticles, such as HIV virus, is a critical step in clinical diagnosis. However, it often requires sophisticated infrastructure that is not easily accessible in resource limited environment. Microfluidics is a promising solution to biological sample processing and diagnostics at the point of need because the ability to use very small quantities of samples and reagents, and to carry out separations and detections with high resolution and sensitivity; low cost; short time for analysis; and small footprints for the analytical devices. By studying migration of nanoparticles by gravity or temperature gradient, we designed devices that can focus and separate nanoparticles.Clinical analysis of acute viral infection in blood requires the separation of viral particles from blood cells, since cytoplasmic enzyme inhibits the subsequent viral detection. To facilitate this procedure in settings without access to a centrifuge, we present a microfluidic device to continuously purify bionanoparticles from cells based on their different intrinsic movements on the microscale. Also, lateral flow introduced by gravity which serves as key for particle separation was quantified.Enriching nanoparticles, both biological and synthetic in a solution, is commonly practiced for various applications. A general method to focus nanoparticles in a microfluidic channel in a label free and continuous flow fashion is not yet available, due to a dominant Brownian force on the nanoscale. Recent research of thermophoresis indicates that thermophoretic force can overcome Brownian force to direct nanoparticle movement. Coupling thermophoresis with natural convection on the microscale has been shown to induce significant enrichment in a closed capillary. However, the sample volume and throughput are not practical, due to difficulty to control thermophoretic and the naturally convective transport independently, and the concentrated samples are hard to retrieve. We designed a microfluidic device to couple artificial recirculation with thermophoresis which allows effective nanoparticle focusing and continuous sample retrieval from the outlet. Numerical analysis studies how the microfluidic geometry and flow condition controls the focusing effect. The results demonstrate that the ratio between the thermophoretic and convective fluxes governs the concentration factor, which reaches maximum when the ratio is approximate one. Microfluidic device was also designed and assembled to reveal the physical processes behind the concentration phenomena and show nanoparticles focusing by one order of magnitude.