Browsing by Subject "Chemical detectors"
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Item Approaches and evaluation of architectures for chemical and biological sensing based on organic thin-film field-effect transistors and immobilized ion channels integrated with silicon solid-state devices(2007) Fine, Daniel Hayes, 1978-; Dodabalapur, Ananth, 1963-There is significant need to improve the sensitivity and selectivity for detecting chemical and biological agents. This need exists in a myriad of human endeavors, from the monitoring of production of consumer products to the detection of infectious agents and cancers. Although many well established methodologies for chemical and biological sensing exist, such as mass spectrometry, gas or liquid phase chromatography, enzymelinked immunosorbent (ELISA) assays, etc., it is the goal of the work described herein to outline aspects of two specific platforms which can add two very important features, low cost and portability. The platforms discussed in this dissertation are organic semiconductor field-effect transistors (OFETS), in various architectural forms and chemical modifications, and ion channels immobilized in tethered lipid bilayers integrated with solid state devices. They take advantage of several factors to make these added features possible, low cost manufacturing techniques for producing silicon and organic circuits, low physical size requirements for the sensing elements, the capability to run such circuits on low power, and the ability of these systems to directly transduce a sensing event into an electrical signal, thus making it easier to process, interpret and record a signal. In the most basic OFET functionality, many types of organic semiconductors can be used to produce transistors, each with a slightly different range of sensitivities. When used in concert, they can produce a reversible chemical "fingerprint". These OFETS can also be integrated with silicon transistors - in a hybrid device architecture - to enhance their sensitivity while maintaining their reversibility. The organic semiconductors themselves can be chemically altered with the use of small molecule receptors designed for specific chemicals or chemical functional groups to greatly enhance the interaction of these molecules with the transistor. This increases both sensitivity and selectivity for discrete devices. Specially designed nanoscale OFET configurations with individually addressable gates can enhance the sensitivity of OFETS as well. Finally, ion channels can be selected for immobilization in tethered lipid bilayer sensors which are already inherently sensitive to the analyte of choice or can be genetically modified to include receptors for many kinds of chemical or biological agents.Item Dyes and indicators in molecular sensing ensembles : progress toward novel uses of dendrimers and reactands in optical sensing methods(2008-12) Rainwater, John Chance, 1979-; Anslyn, Eric V., 1960-Over the past two decades, the field of molecular sensing has developed into a mature offshoot of molecular recognition, and sensing protocols based on optical signal modulations have enjoyed particularly great success. Such sensing methods are the focus of this dissertation, in which efforts toward the integration of dendrimers and reactands into separate, optically-based sensing platforms are described. To this end, Chapter 1 provides a brief introduction to molecular sensing and its supramolecular underpinnings. The remainder of Chapter 1 is dedicated to dendrimers and their application to molecular recognition and sensing. A discussion of the physicochemical properties of dendrimers is also included to lend perspective on the structure, size, and shape of these macromolecules. The role of dyes and indicators in the elucidation of dendritic structure and function is given special consideration. Finally, selected reports of dendrimers in molecular recognition and optical sensing are summarized. Chapter 2 details original research directed toward the incorporation of dendrimers into molecular sensing ensembles. This use of dendrimers in molecular recognition and sensing is distinguished from those examples described in Chapter 1 by its modular nature. This modularity is achieved through the use of a non-covalent sensing motif based on indicator displacement. The identification and optimization of the appropriate components for use in such dendrimer-based sensing ensembles represents a contribution of the research described herein. An evaluation of indicator dyes for their incorporation into an enantioselective indicator displacement assay (eIDA) for common organic molecules is the subject of the research discussed in Chapter 3. The selected indicator dyes were assessed for use in a novel eIDA that relies on covalent bond formation for the enantioselective signaling of monofunctional organic analytes. A survey of colorimetric methods for the identification and discrimination of amines is included because these compounds served as an initial target in the proposed assay. Optical enantiosensing strategies are also reviewed in light of their relevance to the present work.Item Mems based bead size selection method for the electronic taste chip(2004) Park, Byunghwa; Neikirk, Dean P.A micromachined biological and chemical sensor array has been developed for the rapid characterization of multiple analytes in solution. Various biochemical and chemical sensors are loaded in small micromachined structure together to analyze the ingredients in the fluid. Each sensors give unique optical signals under specific conditions that are acquired simultaneously by charge- coupled-device (CCD) optical detectors and those signal patterns are recognized as taste information. A novel micromachined structure has been added to the prototype structure for better performances in many parts. Surface micromachined structures confine sensor beads in the micromachined cavity as well as select designated sensor beads by way of size sorting method. This size selection method utilizes two separate size selective sieves on both sides of micromachined sensor cavities in the electronic taste chip. Each sensor is marked by certain size and selected by designated sensor cavity. Most preferred container of biochemical and chemical sensors is agarose beads. Agarose gel beads have the open pore structure which gives good attachment and binding to biological and chemical sensors. The structural characteristics of agarose bead are investigated and appropriate environment for agarose bead size selection method has been suggested. This research may be very useful in a micro total analysis system technology.Item Nanomaterials characterization and bio-chemical sensing using microfabricated devices(2004) Yu, Choongho, 1971-; Shi, Li, Ph. D.A variety of nanostructured materials have been synthesized in recent years. These nanomaterials have potential applications in areas spanning computing, energy conversion, sensing, and biomedicine. Because of size confinement effects, furthermore, these nanomaterials are expected to show very different physical properties from those of their bulk counterparts. The measurement of their properties, however, has been very challenging due to their small dimensions. Similarly, it remains a challenge to detect chemical and biomolecular species due to their small dimensions. This dissertation presents the development of microelectromechanical systems (MEMS) devices for the characterization of thermophysical properties of nanomaterials and for the detection of chemical species and biological cells. The thermophysical property of one-dimensional (1D) nanomaterials was measured using a batch-fabricated microdevice consisting of two adjacent symmetric silicon nitride membranes suspended by long silicon nitride beams. Three methods were developed to assemble nanomaterials with the measurement devices. Those three methods include a wet deposition process, an in-situ chemical vapor deposition technique, and an electric-field-assisted assembly method. During the measurement, one membrane is Joule-heated to cause heat conduction through the nanomaterials to the other membrane, allowing for the measurement of thermal conductance and Seebeck coefficient. The electrical conductance can also be measured using the microdevice. The temperaturedependent properties of an individual single-wall carbon nanotubes (SWCNs) and SWCN bundles were measured. Measurement sensitivity, errors, and uncertainty were examined. The obtained thermal conductivity of an individual SWCN is found to be much higher than bundles of SWCNs in the range of 2000-11000 W/m-K at room temperature, in agreement with theoretical predictions. Furthermore, the thermal conductivity of bundles of SWCNs are found to be suppressed by contact resistance between interconnected SWCNs in the bundle. The microdevice has also been integrated with metal oxide nanobelts for chemical sensing. The sensing mechanism is based on surface oxidation-reduction (redox) processes that change the electrical conductance of the nanobelt. The sensor was found to be highly sensitive to inflammable and toxic gas species including nitrogen dioxide (NO2), ethanol, and dimethyl methylphosphonate (DMMP). Furthermore, it eliminated the sensor poisoning effects that have limited the wide use of polycrystalline metal-oxide based sensors. The experiment is a step towards the large scale integration of nanomaterials with microsystems, and such integration via an electric-field-directed assembly approach can potentially enable the fabrication of low-power, ultra-sensitive, and selective integrated nanosensor systems. The electric field manipulation technique has not only been used to assemble nanomaterials with MEMS, but also been used to focus biological cells in a microfluidic channel for cytometry applications. Flow cytometry is a powerful and versatile method of rapidly analyzing large populations of cells and other particulate or molecular analytes that have been captured on the surface of carrier particles. However, the key components of the system, hydrodynamic focusing and optical systems, make conventional cytometers complex, large, and expensive. To eliminate these drawbacks, a dielectrophoretic particle focusing technique combined with MEMS is explored to replace the hydrodynamic focusing mechanism. To focus particles, microelectrodes are patterned on the circumference of the channel to generate AC fringing fields that result in negative dielectrophoretic forces directing cells from all directions to the center of the channel. An ellipticlike microfluidic channel has been fabricated by isotropic etching of soda lime glass wafers and a subsequent wafer-bonding process. Experiments with microbeads and human leukemia HL60 cells and an analysis using a thin shell model indicate that biological cells can be focused using an AC voltage of an amplitude up to 15 Vp-p and a frequency below 100 kHz, respectively. This design eliminates the sheath flow and the fluid control system that makes conventional cytometers bulky, complicated, and difficult to operate, and offers the advantages of a portable standalone instrument as well as a module that could potentially be integrated with on-chip impedance or optical sensors into a micro total analysis system.Item Nanoscale organic and polymeric field-effect transistors and their applications as chemical sensors(2005) Wang, Liang; Dodabalapur, Ananth, 1963-This work mainly focused on fabricating of nanoscale polycrystalline organic and conjugated polymeric thin-film field-effect transistors and investigating their scaling behaviors of electrical transport and chemical sensing properties. Devices with channel lengths systematically ranging from a few hundred microns down to sub 10 nm were successfully fabricated with the techniques such as stencil mask, photolithography, electron beam lithography, and break junction. The use of a novel four-terminal geometry ensures that the active area for charge transport and vapor sensing is truly nanoscale, and eliminates undesirable spreading currents traveling over the large area outside the defined channel to reduce the background signal level. It was discovered that upon scaling channel lengths from micron scale down to nanoscale, the dominating factors for charge transport and vapor sensing in organic thin-film transistors become different. At small dimensions, injection limited transport and field-dependent mobility are the dominant mechanisms for transport through the gate-modulated channel at low and high longitudinal fields respectively. Furthermore for sub 10 nm channels, tunneling effect plays an important role. In micron scale devices, the drain current usually decreases as a sensing response upon exposure of the polycrystalline organic/polymeric semiconductor layer to the analyte, mainly because of the transistor threshold shift caused by the immobile charges at grain boundaries trapped by the dipolar analyte molecules. The vapor sensing behavior of nanoscale organic transistors is markedly different (in an opposite direction of response) from that of large-scale devices for the same analyte-semiconductor combination, due to the fact that the electrical transport in a nanoscale OTFT depends on its morphological structure and interface properties (such as the injection barrier at the metal-organic semiconductor contacts) which could be modulated by the delivery of analyte.Item Optical signaling strategies for use in a multi-component sensor array(2003-08) McCleskey, Shawn Catherine, 1976-; McDevitt, John Thoma; Anslyn, Eric V., 1960-This dissertation consists of four chapters that focus on various methods and signaling strategies by which different analytes in solution can be detected within a multi-component sensor array. The first chapter of this dissertation is a review of recent work in the area of chemical sensing. A discussion is provided here of the concepts and basic mechanisms required for a sensing event and different approaches to designing molecular receptors. Next, chemical sensing is described through examples of detection strategies documented in the literature. The introductory chapter concludes by relating different sensory mimics to current methods for vapor and solution phase analyte detection using multicomponent sensor arrays and discussing the importance of pattern recognition protocols for the successful application of sensor arrays. Chapter 2 discusses competitive indicator-displacement methods for the solution-based UV-Visible analysis of citrate and calcium in beverages. A host compound containing three guanidinium moieties on a triethylbenzene core is employed to bind citrate. Improvements to the sensing scheme via complexometric dyes known to bind calcium ion and the host are described. Application of artificial neural networks to the spectral data also allowed for the evaluation of citrate and calcium concentrations in flavored vodkas. Chapter 3 describes a new sensing protocol by coupling a combinatorial library of resin-bound receptors to a multi-component sensor array. The anchored receptor includes a rationally designed scaffold with peptide libraries and is used to bind various nucleotide phosphates. Analyte detection is accomplished by a competition assay using fluorescein as the signaling compound. Principal component analysis shows that the sensing ensembles create a fingerprint response for each compound analyzed in the sensor array. Chapter 4 applies the combinatorial array sensor system described in the previous chapter toward the detection of nerve agent hydrolysis products. First, the synthesis of a control resin-bound peptide library is presented to elucidate the role of the scaffold plays in binding analytes. Studies that lend to an understanding of the sensing protocol mechanism are discussed next in the context of redesigning and optimizing assay conditions. The importance of data processing on the outcome of the principal component analysis is also described. Finally, ideas for expanding the utility of this sensing protocol toward the detection of other classes of analytes via the combinatorial approach are proposed.Item Smart microplates: integration of photodiode within micromachined silicon pyramidal cavity for detecting chemiluminescent reactions and methodology for passive RFID-type readout(2007-12) Park, Yoon Sok, 1977-; Neikirk, Dean P., 1957-Since the late 1990s our group has been working with groups in chemistry department at the University of Texas at Austin on a project referred as "Electronic Taste Chip," a MicroElectroMechanical System (MEMS) based miniaturized microfluidic chemical sensor with multianalyte detection capabilities. By integrating optical detection mechanism directly onto the silicon chip a cost effective, compact, and portable sensor can be realized enabling use of these chips out of conventional laboratory environment. Addition to the integration a noble approach of accessing a photodiode with non-contact powerless RFID type readout is presented. By doing so a packaged photodiode can be interrogated without direct electrical contact, enhancing the portability even further for a sensor operated in aqueous medium. First background information regarding the project as well as design and integration criteria is presented followed by demonstration of non-contact RFID-type readout of a photodiode. Detailed discussion on the development of process integration scheme is discussed along with the measurements verifying the performance of the fabricated photodiode. During this investigation normally overlooked design criteria of collection efficiency, the effect of how a target element is to be delivered to a detection mechanism on the overall performance of the sensor, is addressed and discussed.Item Studies of applying supramolecular chemistry to analytical chemistry(2008-12) Hewage, Himali Sudarshani, 1971-; Anslyn, Eric V., 1960-Supramolecular chemists can be thought of as architects, who combine individual non-covalently bonded molecular building blocks, designed to be held together by intermolecular forces to create functional architectures. Perhaps the most important assets of a supramolecular chemist, however, are imagination and creativity, which have given rise to a wide range of beautiful and functional systems. For years, analytical chemistry has taken advantage of supramolecular assemblies in the development of new analytical methods. The role of synthetic supramolecular chemistry has proven to be a key component in this multidisciplinary research. As such, the demand for synthetic receptors is rapidly increasing within the analytical sciences. The field “supramolecular analytical chemistry” involves analytical applications of synthetic organic and inorganic chemical structures that display molecular recognition properties and self-assembly but also signal these events. Chapter 1 presents an introduction to the background literature relevant to the central themes of the research presented in this thesis. The nonthermal production of visible light by a chemical reaction leads to the term “cool light”, and the process is called chemiluminescence. Although chemiluminescent reactions are not rare, the production of “cool light” holds such fascination for both chemists and nonchemists that demonstrations of chemiluminescent reactions are always well received. A glow assay technology for the detection of a chemical warfare simulant is presented in Chapter 2, which is based on modulating the peroxyoxalate chemiluminescence pathway by way of utilizing an oximate super nucleophile that gives an off-on glow response. As an alternative to highly analyte-specific synthetic receptors, trends in chemical sensing have shifted to the design of new materials and devices that rely on a series of chemo- or biosensors. The research relevant to Chapter 3 focuses on investigating the use of a single receptor, for sensing two different analytes; thiols and metal ions, utilizing a squaraine as the receptor in a sensor array format. The data is interpreted with principal component analysis. Finally Chapter 4 discusses an attempt to design and synthesize a chemosensor based on the luminophore-spacer-receptor format by incorporating the two concepts photoinduced electron transfer and peroxyoxalate chemiluminescence.