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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2022)

As the microfluidic technology has been attracted more attentions and has potential for wide range of applications, in our research work we are utilizing this technique to expand its capability in different aspects of study. In this dissertation, I am going to present two topics of the work: Molecular interaction study using microfluidic techniques and Microfluidic droplet-based applications on single-cell analysis.Biosensors are powerful analytical tools for many applications including drug discovery, medical diagnostics, and environment monitoring. Because of the advance of microfluidic technology, biosensors have a significant improvement by merging the biosensor into lab-on-chip (LOC) technology. In most of the microfluidic sensor, the detection mechanism is through the reaction event that occurs when the flowing analyte in the channel physically or chemically react with the immobilized reactant. The immobilization of recognition elements is needed prior to the sample detection, but this can be a disadvantage of using microfluidic device due to one-time use only. To address this issue, we develop a new readout technique, “Transient Induced Molecular Electronic Signal (TIMES)”. The measured signal from TIMES is directly coming from the induced charge generated from the analyte or chemical reaction, and no immobilization of reactant on electrode surface is needed. I am going to present the work on protein-ligand study based on our microfluidic TIMES measurements, which is a highly potential study in drug discovery research area. Besides, TIMES technique has potential to be an alternative readout for lateral flow assay (LFA) study. The recent work we have done with paper-based TIMES study for antibodies binding interaction will be presented. In the second topic, I am going to show our development on microfluidic device that used for single-cell analysis. There are two main workflows to perform single cell analysis: 1.) Plate-based method and 2.) Droplet-based method. The plate-based method is the traditional way, it is costly and time consuming. While in second method, the cells are encapsulated into small droplet, and all the reaction can be done in this tiny droplet, having capability to operate more than 10,000 cells in one reaction, so it saves more use of reagent and time on operation. In our study, we are trying to identify specific cell subtype by using enhancer screening with droplet-based analysis. However, the droplet manipulation is needed in this procedure. To be specific, droplet merging and double emulsion formation are two main steps in droplet-based analysis. Droplet merging is achieved for reagent addition after cells are lysed and RNA is released in the droplet. In our work, we developed a new microfluidic platform to merge droplets by using pillar-induced mechanism. The double emulsion is another main technique for droplet-based analysis. The main purpose for double emulsion formation is to make droplets compatible to water phase so the targeted droplets can be sorted with FACS equipment. In our study, we are going to expand its application on relating cell morphology to gene expression. The double emulsion technique is applied with image-guided sorting system that developed in our lab and combined with gene sequencing will provide value information for cell genotype-phenotype analysis.

    Cover page: I. Transient Induced Molecular Electronic Spectroscopy (TIMES) technique to study the biomolecular interaction on the surface II. Microfluidic droplet-based techniques for single-cell study
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2019)
    Charge density and molecular coverage on the surface of electrode play major roles in the science and technology of surface chemistry and biochemical sensing. However, there has been no easy and direct method to characterize these quantities. By extending the method of Transient Induced Molecular Electronic Signal (TIMES) which we have used to measure molecular interactions, we are able to quantify the amount of charge in the double layers at the solution/electrode interface for different buffer strengths, buffer types, and pH values. Most uniquely, such capabilities can be applied to study surface coverage of immobilized molecules. As an example, we have measured the surface coverage for thiol-modified single-strand deoxyribonucleic acid (ssDNA) as anchored probe and 6-Mercapto-1-hexanol (MCH) as blocking agent on the platinum surface. Through these experiments, we demonstrate that TIMES offers a simple and accurate method to quantify surface charge and coverage of molecules on a metal surface, as an enabling tool for studies of surface properties and surface functionalization for biochemical sensing and reactions.
      Cover page: Measuring Electric Charge and Molecular Coverage on Electrode Surface from Transient Induced Molecular Electronic Signal (TIMES)
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2021)
      The microfluidic-based, label-free image-guided cell sorter offers a low-cost, high information content, and disposable solution that overcomes many limitations in conventional cell sorters. However, flow confinement for most microfluidic devices is generally only one-dimensional using sheath flow. As a result, the equilibrium distribution of cells spreads beyond the focal plane of commonly used Gaussian laser excitation beams, resulting in a large number of blurred images that hinder subsequent cell sorting based on cell image features. To address this issue, we present a Bessel-Gaussian beam image-guided cell sorter with an ultra-long depth of focus, enabling focused images of >85% of passing cells. This system features label-free sorting capabilities based on features extracted from the output temporal waveform of a photomultiplier tube (PMT) detector. For the sorting of polystyrene beads, SKNO1 leukemia cells, and Scenedesmus green algae, our results indicate a sorting purity of 97%, 97%, and 98%, respectively, showing that the temporal waveforms from the PMT outputs have strong correlations with cell image features. These correlations are also confirmed by off-line reconstructed cell images from a temporal-spatial transformation algorithm tailored to the scanning Bessel-Gaussian beam.
        Cover page: Label-free image-encoded microfluidic cell sorter with a scanning Bessel beam.
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