Development of phase-resolved optical Doppler tomography for imaging and quantifying flow dynamics and particle size in microfluidic channels

The understanding of local flow dynamics is very important to the design, manufacture and operation of Lab-on-a-chip systems, due to scaling-down effects and complicated microscale interactions. The goal of this dissertation is to develop optical Doppler tomography (ODT), which utilizes low-coherence interferometry to perform high-resolution cross-sectional mapping of microflows, as a multi-functional system for quantitative diagnostic flow dynamics, microscale effects and particle sizing in microfluidic systems. This first part of this dissertation describes the basic principles of ODT and fundamental flow mechanics. Understanding them ensures appropriate studies of microflow dynamics. The second part of this dissertation discusses the implementation of microfluidic probe station (MPS) based on ODT. The capabilities and strengths of the MPS for diagnostic of microflow dynamics are first demonstrated in the third part. The investigations include flow profiles resulting from different driven forces, flows within different geometrical microchannels and electroosmotic mobility of electrolytes. Bi-directional flows induced by microscale effects within a single microchannel have been imaged and quantified for the first time.; The fourth part of the dissertation consists of the development of axial scanning free ODT system, which utilizes parallel detection and is demonstrated for fast flow diagnostic. Until recently, phase-resolved ODT systems have not been capable of imaging and quantifying fast flow dynamics because of the limitation of axial mechanic scanning devices. The measurement of biological tissues as well as flows through microchannels is presented using this new developed technique.; In addition to the capability of investigating microflow dynamics, the phase-resolved ODT has also been developed for particle sizing. The relationship between Doppler variance and broadening has been experimentally verified. Experiments of imaging particles with different wavelengths and probing particles within microchannels are presented.