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Open Access Publications from the University of California

Scholarly Works (6 results)

  • Thesis
  • Peer Reviewed
UC Irvine Electronic Theses and Dissertations (2015)

Particle sorting, counting, and separation are crucial precursor steps to a host of biomedical assays, and various macroscale tools have been developed over the past several decades in response. In more recent years, microfluidic technologies have gained significant popularity as a means of performing these same tasks and more, all at reduced power, reagent volume, time, and user difficulty. This raises the possibility that every fluidic, optical, and electronic system in a biomedical laboratory could soon be reduced to a microscale equivalent, and incorporated onto a single handheld device, a hypothetical lab-on-a-chip. However, while the sorting technologies at the heart of this new class of device have developed at a dramatic pace, the devices themselves remain costly to fabricate, difficult to manufacture at large scales, and poorly integrated with auxiliary systems such as power supplies and peristaltic pumps. As such, they rarely develop beyond the proof-of-concept stage and have yet to achieve any significant acceptance in the biomedical community. This work seeks to move microfluidic sorters beyond this obstacle. First, it was demonstrated that multiple components could be implemented onto a single platform, eliminating cumbersome external fluidics in the process. Next, methods from the mature microelectronics industry were used to build an electronic microfluidic cell sorter on a printed circuit board platform, yielding a dramatic improvement in device manufacturability and user friendliness, as well as ease of integration with other electronics, micro or otherwise. Finally, building on this, a method was developed to manufacture large numbers of three-dimensional microelectrodes and then incorporate them into a microfluidic device using pick-and-place methods, again a technique adapted from the microelectronics industry. Together, this shifts microfluidics away from the established standard of cumbersome devices monolithically constructed using costly materials and methods and towards a novel standard of more manufacturable and user-friendly devices, and represents a step towards this class of device gaining mainstream acceptance in the biomedical community.

    Cover page: Integrated Microfluidic Systems for Continuous Particle Sorting
    • Article
    • Peer Reviewed
    UC Irvine Previously Published Works (2014)
    We report the development and results of a two-step method for sorting cells and small particles in a microfluidic device. This approach uses a single microfluidic channel that has (1) a microfabricated sieve which efficiently focuses particles into a thin stream, followed by (2) a dielectrophoresis (DEP) section consisting of electrodes along the channel walls for efficient continuous sorting based on dielectric properties of the particles. For our demonstration, the device was constructed of polydimethylsiloxane, bonded to a glass surface, and conductive agarose gel electrodes. Gold traces were used to make electrical connections to the conductive gel. The device had several novel features that aided performance of the sorting. These included a sieving structure that performed continuous displacement of particles into a single stream within the microfluidic channel (improving the performance of downstream DEP, and avoiding the need for additional focusing flow inlets), and DEP electrodes that were the full height of the microfluidic walls ("vertical electrodes"), allowing for improved formation and control of electric field gradients in the microfluidic device. The device was used to sort polymer particles and HeLa cells, demonstrating that this unique combination provides improved capability for continuous DEP sorting of particles in a microfluidic device.
      Cover page: Microfluidic dielectrophoretic sorter using gel vertical electrodes
      • Article
      • Peer Reviewed
      UC Irvine Previously Published Works (2014)
      We report the development and results of a two-step method for sorting cells and small particles in a microfluidic device. This approach uses a single microfluidic channel that has (1) a microfabricated sieve which efficiently focuses particles into a thin stream, followed by (2) a dielectrophoresis (DEP) section consisting of electrodes along the channel walls for efficient continuous sorting based on dielectric properties of the particles. For our demonstration, the device was constructed of polydimethylsiloxane, bonded to a glass surface, and conductive agarose gel electrodes. Gold traces were used to make electrical connections to the conductive gel. The device had several novel features that aided performance of the sorting. These included a sieving structure that performed continuous displacement of particles into a single stream within the microfluidic channel (improving the performance of downstream DEP, and avoiding the need for additional focusing flow inlets), and DEP electrodes that were the full height of the microfluidic walls ("vertical electrodes"), allowing for improved formation and control of electric field gradients in the microfluidic device. The device was used to sort polymer particles and HeLa cells, demonstrating that this unique combination provides improved capability for continuous DEP sorting of particles in a microfluidic device.
        Cover page: Microfluidic dielectrophoretic sorter using gel vertical electrodesCreative Commons 'BY-NC-ND' version 4.0 license
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2016)
        We present a microfluidic lab-on-printed circuit board (PCB) device containing alloy vertical electrodes for sorting microparticles using dielectrophoresis. The device consists of a hydrodynamic prefocuser and an electronic sorting region. Lining the two sidewalls of the electronic sorting region are regularly spaced rectangular metal electrodes reaching from the floor to the ceiling of the flow channel that bridge electric field lines laterally across the channel. The size and distribution of these vertical electrodes are arranged asymmetrically such that the resultant electric field forms sharp electric field gradients across the channel; specific geometries were optimized using finite element methods. Particles entering the device are initially focused on a single stream as they pass through the prefocuser. Subsequently, they are exposed to the lateral electric field gradient and separate into streams based on their size and dielectric properties. Validation was performed by dielectrophoretically separating live cells from dead cells. Importantly, the system presented can be readily integrated with various external sensors and actuators using commercially available components owing to the device's integration into a PCB.
          Cover page: 3-D In-Bi-Sn Electrodes for Lab-on-PCB Cell Sorting
          • Article
          • Peer Reviewed
          UC Santa Barbara Previously Published Works (2017)
          Helical 1D electronic systems are a promising route towards realizing circuits of topological quantum states that exhibit non-Abelian statistics. Here, we demonstrate a versatile platform to realize 1D systems made by combining quantum Hall (QH) edge states of opposite chiralities in a graphene electron-hole bilayer at moderate magnetic fields. Using this approach, we engineer helical 1D edge conductors where the counterpropagating modes are localized in separate electron and hole layers by a tunable electric field. These helical conductors exhibit strong non-local transport signals and suppressed backscattering due to the opposite spin polarizations of the counterpropagating modes. Unlike other approaches used for realizing helical states, the graphene electron-hole bilayer can be used to build new 1D systems incorporating fractional edge states. Indeed, we are able to tune the bilayer devices into a regime hosting fractional and integer edge states of opposite chiralities, paving the way towards 1D helical conductors with fractional quantum statistics.
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2022)
            Proprioception is critical to motor control and functional status but has received limited study early after stroke. Patients admitted to an inpatient rehabilitation facility for stroke (n = 18, mean(±SD) 12.5 ± 6.6 days from stroke) and older healthy controls (n = 19) completed the Wrist Position Sense Test (WPST), a validated, quantitative measure of wrist proprioception, as well as motor and cognitive testing. Patients were serially tested when available (n = 12, mean 11 days between assessments). In controls, mean(±SD) WPST error was 9.7 ± 3.5° in the dominant wrist and 8.8 ± 3.8° in the nondominant wrist (p = 0.31). In patients with stroke, WPST error was 18.6 ± 9° in the more-affected wrist, with abnormal values present in 88.2%; and 11.5 ± 5.6° in the less-affected wrist, with abnormal values present in 72.2%. Error in the more-affected wrist was higher than in the less-affected wrist (p = 0.003) or in the dominant (p = 0.001) and nondominant (p < 0.001) wrist of controls. Age and BBT performance correlated with dominant hand WPST error in controls. WPST error in either wrist after stroke was not related to age, BBT, MoCA, or Fugl-Meyer scores. WPST error did not significantly change in retested patients. Wrist proprioception deficits are common, bilateral, and persistent in subacute stroke and not explained by cognitive or motor deficits.
              Cover page: Wrist Proprioception in Adults with and without Subacute Stroke.
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