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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2016)

The ability to manipulate biological cells and micrometer-scale particles plays an important role in many biological and colloidal science applications. However, conventional manipulation techniques, such as optical forces, electrokinetic forces (electrophoresis, dielectrophoresis (DEP), and traveling-wave dielectrophoresis), magnetic forces, acoustic forces (surface standing acoustic waves (SAW), and bulk standing acoustic waves(BAW)), and hydrodynamic flows, cannot achieve high resolution and high throughput at the same time. While electrokinetic forces and other mechanisms provide higher throughput than optical mechanism, but lack the flexibility or the spatial resolution necessary for controlling individual particles. None of which could provide high resolution, throughput and versatility in clinical applications.

In this dissertation, I present a novel DEP concept for high resolution, throughput and versatility microns-sized particle and biological cell manipulation in high-speed flows. Using novel three-dimensional (3D) polydimethylsiloxane (PDMS) thin-film fabrication platform I developed, true heterogeneous integration of electronics on hard substrates (silicon and/or glass) and PDMS are demonstrated for the first time to create 3D electric field across the entire large area (couple centimeter across) 3D microfluidic channel networks. Which enables broad applications, such as sheathless sub-micron particle focusing in high-speed flows, tunable micron-sized particle and cell focusing in high-speed flows, and ultra-high precision particle size-based sorting. Within all sections, experiments were performed with beads to verify the concept of each platform and then with cells to demonstrate qualitative and quantitative operation of the performance. These technologies is now well poised to enable the development of biological assays that are currently unavailable.

    Cover page: High-Speed Dielectrophoresis and 3D Microfluidics for Biological Applications
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2015)
    We report a novel methodology for fabricating large-area, multilayer, thin-film, high aspect ratio, 3D microfluidic structures with through-layer vias and open channels that can be bonded between hard substrates. It is realized by utilizing a hybrid stamp with a thin plastic sheet embedded underneath a PDMS surface. This hybrid stamp solves an important edge protrusion issue during PDMS molding while maintaining necessary stamp elasticity to ensure the removal of PDMS residues at through-layer regions. Removing edge protrusion is a significant progress toward fabricating 3D structures since high aspect ratio PDMS structures with flat interfaces can be realized to facilitate multilayer stacking and bonding to hard substrates. Our method also allows for the fabrication of 3D deformable channels, which can lead to profound applications in electrokinetics, optofluidics, inertial microfluidics, and other fields where the shape of the channel cross section plays a key role in device physics. To demonstrate, as an example, we have fabricated a microfluidic channel by sandwiching two 20 μm wide, 80 μm tall PDMS membranes between two featureless ITO glass substrates. By applying electrical bias to the two ITO substrates and pressure to deform the thin membrane sidewalls, strong electric field enhancement can be generated in the center of a channel to enable 3D sheathless dielectrophoretic focusing of biological objects including mammalian cells and bacteria at a flow speed up to 14 cm s(-1).
      Cover page: Fabrication of 3D high aspect ratio PDMS microfluidic networks with a hybrid stamp
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2013)
      We report a 3D microfluidic pulsed laser-triggered fluorescence-activated cell sorter capable of sorting at a throughput of 23 000 cells per s with 90% purity in high-purity mode and at a throughput of 45 000 cells per s with 45% purity in enrichment mode in one stage and in a single channel. This performance is realized by exciting laser-induced cavitation bubbles in a 3D PDMS microfluidic channel to generate high-speed liquid jets that deflect detected fluorescent cells and particles focused by 3D sheath flows. The ultrafast switching mechanism (20 μs complete on-off cycle), small liquid jet perturbation volume, and three-dimensional sheath flow focusing for accurate timing control of fast (1.5 m s(-1)) passing cells and particles are three critical factors enabling high-purity sorting at high-throughput in this sorter.
        Cover page: 3D pulsed laser-triggered high-speed microfluidic fluorescence-activated cell sorter
        • Article
        • Peer Reviewed
        UC Merced Previously Published Works (2014)
        The roles of virus-derived small RNAs (vsRNAs) have been studied in plants and insects. However, the generation and function of small RNAs from cytoplasmic RNA viruses in mammalian cells remain unexplored. This study describes four vsRNAs that were detected in enterovirus 71-infected cells using next-generation sequencing and northern blots. Viral infection produced substantial levels (>10(5) copy numbers per cell) of vsRNA1, one of the four vsRNAs. We also demonstrated that Dicer is involved in vsRNA1 generation in infected cells. vsRNA1 overexpression inhibited viral translation and internal ribosomal entry site (IRES) activity in infected cells. Conversely, blocking vsRNA1 enhanced viral yield and viral protein synthesis. We also present evidence that vsRNA1 targets stem-loop II of the viral 5' untranslated region and inhibits the activity of the IRES through this sequence-specific targeting. Our study demonstrates the ability of a cytoplasmic RNA virus to generate functional vsRNA in mammalian cells. In addition, we also demonstrate a potential novel mechanism for a positive-stranded RNA virus to regulate viral translation: generating a vsRNA that targets the IRES.
          Cover page: A cytoplasmic RNA virus generates functional viral small RNAs and regulates viral IRES activity in mammalian cells
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