Browsing by Author "Du, Nan"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    A disposable bio-nano-chip usuing agarose beads for protein analysis
    (2012) Du, Nan; McDevitt, John T.
    This thesis reports on the fabrication of a disposable bio-nano-chip (BNC), a microfluidic device composed of polydimethylsiloxane (PDMS) and thiolene-based optical epoxy which is both cost-effective and suitable for high performance immunoassays. A novel room temperature (RT) bonding technique was utilized so as to achieve irreversible covalent bonding between PDMS and thiolene-based epoxy layers, while at the same time being compatible with the insertion of agarose bead sensors, selectively arranged in an array of pyramidal microcavities replicated in the thiolene thin film layer. In the sealed device, the bead-supporting epoxy film is sandwiched between two PDMS layers comprising of fluidic injection and drain channels. The agarose bead sensors used in the device are sensitized with anti-C-reactive protein (CRP) antibody, and a fluorescent sandwich-type immunoassay was run to characterize the performance of this device. Computational fluid dynamics (CFD) was used based on the device specifications to model the bead penetration. Experimental data revealed analyte penetration of the immunocomplex to 100μm into the 280μm diameter agarose beads, which correlated well with the simulation. A dose response curve was obtained and the linear dynamic range of the assay was established over 1ng/mL to 50ng/mL with a limit of detection less than 1ng/mL.
  • Thumbnail Image
    Item
    Hot embossed polyethylene through-hole chips for bead-based microfluidicdevices
    (Elsevier, 2013) Chou, Jie; Du, Nan; Ou, Tina; Floriano, Pierre N.; Christodoulides, Nicolaos; McDevitt, John T.; Rice Quantum Institute
    Over the past decade, there has been a growth of interest in the translation of microfluidic systems into real-world clinical practice, especially for use in point-of-care or near patient settings. While initial fabrication advances in microfluidics involved mainly the etching of silicon and glass, the economics of scaling of these materials is not amendable for point-of-care usage where single-test applications forces cost considerations to be kept low and throughput high. As such, a materials base more consistent with point-of-care needs is required. In this manuscript, the fabrication of a hot embossed, through-hole low-density polyethylene ensembles derived from an anisotropically etched silicon wafer is discussed. This semi-opaque polymer that can be easily sterilized and recycled provides low background noise for fluorescence measurements and yields more affordable cost than other thermoplastics commonly used for microfluidic applications such as cyclic olefin copolymer (COC). To fabrication through-hole microchips from this alternative material for microfluidics, a fabrication technique that uses a high-temperature, high-pressure resistant mold is described. This aluminum-based epoxy mold, serving as the positive master mold for embossing, is casted over etched arrays of pyramidal pits in a silicon wafer. Methods of surface treatment of the wafer prior to casting and PDMS casting of the epoxy are discussed to preserve the silicon wafer for future use. Changes in the thickness of polyethylene are observed for varying embossing temperatures. The methodology described herein can quickly fabricate 20 disposable, single use chips in less than 30 minutes with the ability to scale up 4x by using multiple molds simultaneously. When coupled as a platform supporting porous bead sensors, as in the recently developed Programmable Bio-Nano-Chip, this bead chip system can achieve limits of detection, for the cardiac biomarker C-reactive protein, of 0.3 ng/mL, thereby demonstrating the approach is compatible with high performance, real-world clinical measurements in the context of point-of-care testing.
  • Thumbnail Image
    Item
    Microfluidic bio-nano-chip platforms for optimized immunoassay using 3D agarose bead-based biosensors
    (2013-11-07) Du, Nan; McDevitt, John T.; Biswal, Sibani Lisa; Dunning, F. Barry
    This dissertation is devoted to the development of novel bio-nano chip microfluidic platforms suitable for agarose bead-based sensors. Previously, our lab had developed a novel immunoassay sensor based on three-dimensional agarose beads whose surface is marked by micro-size pores. Porous agarose beads have a greater capacity of immobilizing antibodies as compared to other surface based sensors, and thus are expected to yield better assay performance. The first generation of bio-nano-chip platform had been designed to contain an array of three-dimensional wells to host the agarose beads. In the bio-nano-chip platform, a silicon-based bead holder had been designed to generate strong convectional flows around beads and greatly enhance the detection sensitivity. As the silicon microchip was fabricated based on the traditional MEMS techniques, however, the cost of the device remains relatively high. Moreover, the accuracy of the assays and the assay time also need to be improved to meet the standard of point-of-care diagnostics. In efforts to overcome these issues, this dissertation reports works of replacing the material of key components with cheaper materials in the bio-nano-chip platform. Further, this dissertation presents a new mechanism of recirculating assays in a membrane-based chip, and also a new bead design to further enhance the assay performance. In summary, the bio-nano-chip platform had been improved to be more efficient and cost-effective than previous designs, allowing wider applications in resource limited areas such as in developing countries.