Browsing by Author "Wang, Xingwei"

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    Label-free DNA Sequence Detection Using Oligonucleotide Functionalized Fiber Probe with a Miniature Protrusion
    Wang, Xingwei (Virginia Tech, 2006-08-08)
    DNA is the substance that encodes the genetic information that cells need to replicate and to produce proteins. The detection of DNA sequences is of great importance in a broad range of areas including genetics, pathology, criminology, pharmacogenetics, public health, food safety, civil defense, and environmental monitoring. However, the established techniques suffer from a number of problems such as the bulky size, high equipment costs, and time-consuming algorithms so that they are limited to research laboratories and cannot be applied for in-vivo situations. In our research, we developed a novel sensing scheme for DNA sequence detection, featuring sequence specificity, cost efficiency, speed, and ease of use. Without the need for labels or indicators, it may be ideal for direct in-cell application. The principle is simple. With capture DNA immobilized onto the probe by layer-by-layer selfassembly, the hybridization of a complementary strand of target DNA increases the optical thickness of the probe. Three kinds of sensors were developed. The optical fiber tip sensor has been demonstrated with good specificity and high sensitivity for target DNA quantities as small as 1.7 ng. To demonstrate the potential of this structure for practical applications, tularemia bacteria were tested. Two other micrometric structures were designed with specific advantages for different applications. The micro-fiber Bragg grating interferometer (Micro-FBGI) has the intrinsic temperature compensation capability. The micro-intrinsic Fabry-Perot interferometer (Micro-IFPI)features simple signal processing due to its simple configuration. Successful DNA immobilization and hybridization have been demonstrated onto the 25μm Micro-IFPI. Both structures have great potential for nanometric protrusion, allowing future in-cell DNA direct detection. In addition, its quick response time leads to the potential for express diagnosis. What's more, the idea of nanoscale probe has a broad impact in scanning near-field optical microscopy (SNOM), intracellular surgery in cell sensing, manipulation, and injection.
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    Optical fiber pressure and acceleration sensor fabricated on a fiber endface
    (United States Patent and Trademark Office, 2006-05-30)
    A fiber optic sensor has a hollow tube bonded to the endface of an optical fiber, and a diaphragm bonded to the hollow tube. The fiber endface and diaphragm comprise an etalon cavity. The length of the etalon cavity changes when applied pressure or acceleration flexes the diaphragm. The entire structure can be made of fused silica. The fiber, tube, and diaphragm can be bonded with a fusion splice. The present sensor is particularly well suited for measuring pressure or acceleration in high temperature, high pressure and corrosive environments (e.g., oil well downholes and jet engines). The present sensors are also suitable for use in biological and medical applications.
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    Optical Fiber Tip Pressure Sensor
    Wang, Xingwei (Virginia Tech, 2004-10-18)
    Miniature pressure sensors which can endure harsh environments are a highly sought after goal in industrial, medical and research fields. Microelectromechanical systems (MEMS) are the current methods to fabricate such small sensors. However, they suffer from low sensitivity and poor mechanical properties. To fulfill the need for robust and reliable miniature pressure sensors that can operate under high temperatures, a novel type of optical fiber tip sensor only 125μm in diameter is presented in this thesis. The essential element is a piece of hollow fiber which connects the fiber end and a diaphragm to form a Fabry-Pérot cavity. The all-fused-silica structure fabricated directly on a fiber tip has little temperature dependence and can function very well with high resolution and accuracy at temperatures up to 600 °C. In addition to its miniature size, its advantages include superior mechanical properties, biocompatibility, immunity to electromagnetic interference, disposability and cost-effective fabrication. The principle of operation, design analysis, fabrication implementation and performance evaluation of the sensor are discussed in detail in the following chapters.