Browsing by Author "Liu, Chao"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Label-free optical imaging to study brain connectivity and neuropathology
    (2018-11) Liu, Chao
    The brain is composed of billions of neurons that communicate through an intricate network of axons and dendrites. The difficulty of tracing the 3D neuronal pathways, however, has been a challenge to study the brain connectivity in normal and diseased brains. Polarization-sensitive optical coherence tomography (PS-OCT) provides label-free and depth-resolved contrasts of tissue microstructure. For brain imaging, nerve fiber tracts that are as small as tens of micrometers can be highlighted by polarization-based contrasts due to the birefringent nature of myelin sheath. We applied optical imaging to investigate the anatomical changes associated with neurodegeneration and neuro-oncology. The former includes spinocerebellar ataxia type 1 (SCA1), a fatal inherited genetic disease. The intrinsic optical properties revealed the neuropathology in SCA1 mouse models. To investigate the role of nerve fiber tracts in glioblastoma invasion, we combined PS-OCT with confocal fluorescence microscopy to characterize glioma cell migration behavior in mouse brain slices. Moreover, PS-OCT can be adapted to quantify the inclination angles of nerve fibers and further developed to delineate the complete 3D neuronal pathways. This method and its future advances open up intriguing applications in neurological and psychiatric disorders.
  • Thumbnail Image
    Item
    Remote-Controlled Self-Assembly of Three-Dimensional Micro Structures for Ultra-Sensitive Sensors and Three-Dimensional Metamaterials
    (2018-10) Liu, Chao
    Self-assembly has been widely used to fabricate micro-scale three-dimensional (3D) structures for various applications like sensors, drug delivery systems, and advanced robotics (e.g., micro-actuators, micro-machines). Self-assembly is always driven by external sources (e.g., heat, solvent, pH), which makes the assembly process hard to control and leads to extremely low yield. Direct contact of heat or chemicals is usually required to trigger a self-assembly process, which limits the applications of self-assembly and decreases the manipulative capability of the process. To address the issues of the traditional direct triggered self-assembly, my Ph.D. work involved in developing novel remote-controlled self-assembly techniques with microwave and induction energies, combining the self-assembly technique with advanced metamaterial (MM) designs, and exploring their potential applications as 3D sensors and devices. The goal of the work is to achieve advanced remotely controlled self-assembly to improve the yield and manipulative capability of the assembly process and discover new aspects of the assembly technique (e.g., biocompatible assembly, multiple and sequential assembly) and its applications (e.g., 3D sensors, 3D MM devices). For remotely controlled self-assembly, electromagnetic waves can be remotely applied to the metal thin films within the microstructures. Eddy current can be created inside the thin films and generate heat to melt the polymeric hinges. The molten hinges generate surface tension force to transform the two-dimensional (2D) net into 3D microstructures. Induction heating can trigger self-assembly without harming live organs or tissues, which is suitable for biomedical applications. Remote-controlled self-assembly also allows multiple and sequential self-assembly. The movements of each part of structure can be precisely controlled by adjusting the energy sources in a remote location, increasing manipulative capability of the 3D assembly process. The achievement of sequential self-assembly and multiple folding angles in a single structure is essential for building complex microstructures and micro-actuators. One important application for remote-controlled 3D self-assembled structure is to build 3D MM devices. Split ring resonators (SRRs) and closed ring resonators (CRRs) can be patterned on each face of the self-assembled structures to achieve 3D MMs with fully anisotropic and isotropic behaviors. However, the quality factor (Q-factor) of conventional MMs is low (typically under 10), results in low sensitivity and selectivity. To increase Q-factor of the MMs, we developed novel nanopillar-based MMs driven by displacement current. The nanopillar-based MMs contain thousands of metallic nanopillars with nanoscale dielectric gaps between them. Forming the MMs with nanopillars and nano gaps decreases the Ohmic energy loss in the resonator and increases the energy storage in the dielectric nano gaps, thus an enhanced Q-factor up to 14000 can be achieved. The ultra-high Q nanopillar-based MM can be patterned on each face of the self-assembled 3D structures to realize ultra-high Q 3D MM structures. Novel ultra-sensitive THz MMs and 3D MMs combined with remote-controlled self-assembly opens a new area of creating diverse sensors and devices for 3D optoelectronic, 3D MMs, and ultra-high sensitive biomedical sensors. This thesis will be roughly divided into two parts. We begin with part one by introducing the novel remotely controlled self-assembly using electromagnetic energies that I have developed over my Ph.D. program as well as its unique properties and benefits over traditional self-assemblies. The second part involves my design and theory of ultra-high Q nanopillar-based MM and the 3D MM devices by combining the nanopillar-based MM with self-assembly technique.