Browsing by Subject "Biosensors"
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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 Bead based microreactors for sensing applications(2007-05) Wong, Jorge, 1970-; McDevitt, Subject 690 Chemistry. Added Author 720 McDevitt, John T.,esupervisor.Item Bead based microreactors for sensing applications(2007) Wong, Jorge; McDevitt, John T.The dissertation research described here focuses on the fabrication and modification of the polymeric beaded sensing elements, one of the many critical components of a Microbead Array Chip-Based Multianalyte Detection System. Detection of biomolecules including proteins and oligonucleotides are based on affinity interactions between carefully selected ligands immobilized on the sensing microspheres. The current work relies on microspheres made of agarose gel shaped into micron sized beads with intrinsic porosity associated to the concentration of agarose in the gel. The beaded material described is considered of a homogeneous nature with limited transport capabilities although superior to homogeneous latex beads. The microbead array system potentially benefits from structural modifications on the sensing elements and includes improvement on the mobile phase mass transport, capture of larger particles, faster assays, and the increase in the multiplexing capabilities. Efforts are also directed to preferentially modify gels made of agarose to facilitate the transition from the existing sensing elements to the new beaded designs made of the same polysaccharide. As a result the chemistry utilized to attach affinity ligands to procure reactive sensing elements remained practically the same. Collectively, these research activities have resulted in a number of novel polymer-based reactive particles that have the potential to service a variety of new sensing applications.Item Conducting polymer hydrogels for high-performance electrochemical devices(2014-05) Liu, Borui; Yu, Guihua (Assistant professor)Conducting polymer hydrogels (CPHs) is a class of unique materials that synergize the advantages of conducting polymers (CPs) and polymer hydrogels together. It has been employed in many high-performance electrochemical devices for years, such as energy storage and biosensors. However, large limitations of applying CPHs into the abovementioned areas have been facing the researcher for a long time, mainly due to the difficulties from complicated materials synthesis and untenable nanostructures for potential applications. The drawbacks of previously reported CPHs have put numerous disadvantages onto their applications, partially because they have, for example, high prices, untunable microscale or nanoscale architectures, environmentally hazardous properties, and unscalable and time-consuming synthesis processes. In this thesis, we proposed a novel route for carrying out CPHs by one-step organics synthesis at ambient conditions. The CPHs have hierarchically porous nanostructures crosslinked in a three-dimensional (3D) way, which enable its stable mechanical, unique chemical and physical properties, and outstanding electrochemical properties for potential applicability in long-term energy storage devices and highly sensitive biosensors. With highly controllable nanostructures of the CPHs, our novel concept and material system could possibly be utilized in a broad range of electrochemical applications, including but not limited to lithium-ion batteries (LIBs) electrodes, electrochemical capacitors (ECs), biofuel cells, medical electrodes, printable electronic devices, and biosensors.Item Coupling aptamer biosensors to signal amplification(2007-05) Yang, Litao, 1976-; Ellington, Andrew D.; Georgiou, GeorgeNucleic acids amplification methods can be extremely useful for the identification and quantitation of nucleic acid analytes, but are more difficult to adapt to the detection of non-nucleic acid targets. To facilitate the development of nucleic acid amplification for small molecule and protein analytes, we have developed the use of aptazyme and conformation-switching aptamers to generate amplification signals upon interaction with their cognate analytes. We have developed chip-based rolling circle amplification (RCA) for the detection of ATP utilizing a DNA aptazyme that could catalyze the ligation and circularization of a single-stranded DNA substrate upon ATP recognition. The method has demonstrated that aptazyme-coupled chip-based RCA could sensitively detect ATP and the reproducible signals can be easily read and acquired within a few minutes. In addition to the design of aptazyme mediated ligation for the detection of small molecules, we have been interested in the adaptation of structure-switching aptamers to generate analyte-dependent ligations. We have developed a novel type of conformationswitching aptamer that can be circularized by T4 DNA ligase upon interaction with its protein target, PDGF. Using this structure-switching aptamer real-time RCA can be used to quantitate PDGF down to low-nanomolar range, even against a background of cellular lysate. Our results also demonstrate that real-time RCA has advantages over chip-based RCA. Furthermore, we have coupled conformation-switching aptamers with binding to an antisense oligonucleotide in a way that leads to ligation and the formation of a novel amplicon for real-time PCR. We have explored different strategies from four-piece to two-piece ligations. Our results show that the three-piece has sensitivity and simplicity over the four-piece ligation. However, both four-piece and three-piece ligations require ligation time as long as 8 hours, which is not practical for clinical diagnostics. Therefore, we have simplified the detection into a two-piece ligation, where the antisense sequence is attached to the aptamer and upon binding to protein analyte (PDGF or thrombin) the displaced antisense sequence is ligated to a substrate oligonucleotide. By real-time amplification (PCR) of the ligated product we find that the conformation-switching aptamers can sensitively and specifically detect thrombin or PDGF at picomolar level against a background of cellular lysate. The principal advantage of this method is that it can potentially be applied to a wide variety of analytes, thereby allowing the development of numerous amplificable aptamer biosensors.Item Coupling aptamer biosensors to signal amplification(2007) Yang, Litao; Ellington, Andrew D.; Georgiou, GeorgeItem Electrochemical evaluation of nanocarbons for biogenic analyte detection(2007-12) Lyon, Jennifer Lee, 1980-; Stevenson, Keith J.This dissertation explores the use of nanocarbons both as conductive supports for redox enzyme electrochemistry and as electrocatalytic components for the nonmediated detection of biogenic analytes. More specifically, the influence of nitrogen doping of these nanocarbons (referred to herein as nitrogen-doped carbon nanotubes, or N-CNTs) on their bioelectrocatalytic performance is studied through direct enzyme adsorption and exploitation of the N-CNTs' inherent reactivity toward H₂O₂ to create H₂O₂-based sensing strategies. Both nondoped CNTs and N-CNTs may be effectively incorporated into biogenic sensing assemblies, as demonstrated herein using a variety of electrochemical techniques. Chapter 1 gives a general overview of the scope of this research and describes previous studies conducted within our laboratories that demonstrate our CNTs' promise as biogenic electrode materials. Chapter 2 describes the chemical vapor deposition (CVD) method used to prepare both CNTs and N-CNTs and establishes their suitability for use in the detection schemes outlined in later chapters through long-term stability studies. Additionally, the redox activity of Fe nanoparticles entrapped in the CNTs as a result of this CVD growth process is examined using a host of electrochemical experiments. Importantly, the data presented in this chapter show that these Fe particles do not explain the observed electrocatalytic response of the CNTs. Chapter 3 explores the direct adsorption of horseradish peroxidase (HRP) at both nondoped and N-CNTs. Spectroscopic and electrochemical assays are used to compare the extent of HRP enzymatic activity upon immobilization at both types of CNTs. Both types of HRP/CNT composites are then utilized in a quantitative H₂O₂ sensing strategy. Chapter 4 discusses the intrinsic reactivity of N-CNTs toward H₂O₂. Koutecky-Levich plots are used to demonstrate differences in H₂O₂ consumption mechanisms between NCNTs and traditional peroxidases. By replacing HRP with N-CNTs in an amperometric glucose detection scheme, the versatility of N-CNTs as a peroxidase substitute for biogenic analyte detection is demonstrated. Chapter 5 outlines future directions for this research, including possible strategies for improving electron transfer between HRP and both types of CNTs. This chapter also presents a newly developed, mediated oxidase-substrate electrochemical detection method that can easily be modified to incorporate CNTs.Item Establishment of a multipurpose biologically based fiber optic immunosensor(Texas Tech University, 2001-12) Colls, Noel RThe lines between the different scientific fields of study are becoming increasingly blurred. Investigators from all different fields are looking to disparate areas of study for assistance in the progression of science. In light of such a trend, the focus of this project in conjunction with other projects currently underway, is to incorporate various fundamentals from the fields of biology, chemistry, physics, and engineering in order to develop a functional and potentially marketable detection device capable of recognizing virtually any molecular or microbiological target in solution. To that end the physics of light reflecting down a liquid core waveguide and the recognition and capture properties of antibodies were combined in order to develop a multi-purpose antibody-based immunosensor. The capillaries utilized were coated with Teflon® AF. This substance possesses a refractive index lower than that of the wall or the liquid core of the capillary. Therefore a light shone down the axis of the capillary continuously reflected off the inside of the Teflon® coating and emerged out the other end with quantifiable intensity. The lumen wall of the capillary was lined with monoclonal antibodies. The intensity of the light transmitted through the capillary was measurably altered. Human cells contain to specific monoclonal antibodies were then flushed through the capillary and allowed to bind. Cell capture was demonstrated and the light intensity was further altered in a manner that was registered by a spectrometer. Therefore, by incorporating the specific binding nature of monoclonal antibodies, the behavior of light through transparent mediums of differing refractive indices, and precisely machined silica capillaries, we have demonstrated the potential for development of a detection device, or immunosensor, capable of registering very small amounts of a given target in only a few minutes, all in the palm of ones hand.Item Nucleic acid based reagentless optical biosensors(2004-08) Rajendran, Manjula, 1975-; Ellington, Andrew D.Item Nucleic acid biosensors(2003-08) Kirby, Romy, 1972-; Ellington, Andrew D.There is an ever increasing need to expand the realm of diagnostic capabilities. The need for accurate and reliable biological detection methods is crucial for genetic analysis, drug discovery, the monitoring of bacteria and viruses in food and water samples, as well as monitoring the environment for biothreat reagents. In the realm of diagnostics, molecular biology first expanded to include semiconductor manufacturing technology in the creation of a DNA biosensor array. Currently, biosensor arrays are being developed to utilizing complex sensors for the detection of multiple types of analytes. Important to the future applications for biosensor technology is the development of miniaturized systems that utilize sophisticated sensors. We have explored the use of platforms that offer a three-dimensional volume element, as well as sophisticated nucleic acid sensors. A flow cell based microsphere platform (electronic tongue), and a novel hydrogel platform based on shape recognition elements (MUFFINS), have been combined with nucleic acid sensors (ssDNA and aptamers) and fluorescence microscopy to create biosensors for the detection of DNA and proteins. As a step towards fulfilling the goal of developing a second generation of sophisticated sensors, signaling aptamers were engineered. Signaling aptamers are nucleic acid ligands (aptamers) that are capable of displaying changes in fluorescent signal upon binding to their cognate analyte. In addition, “affinity” microspheres were developed for the direct synthesis of microsphere bound nucleic acid sensors.Item Plasmonic nanoparticles for imaging intracellular biomarkers(2007-05) Kumar, Sonia, 1978-; Richards-Kortum, Rebecca, 1964-; Sokolov, Konstantin V. (Associate professor)Molecular optical imaging enables the ability to non-invasively image biological function. When used in conjunction with optical contrast agents, molecular imaging can provide biomarker-specific information with subcellular spatial resolution. Plasmonic nanoparticles are unique optical contrast agents due to the fact that the intensity and peak wavelength of scattering is dependant on interparticle spacing. This distance dependance puts these nanosensors in a position to probe molecular interactions by exploiting contrast between isolated and closely spaced nanoparticles. This dissertation presents the first intracellular molecular imaging platform using multifunctional gold nanoparticles which incorporate both cytosolic delivery and targeting moieties on the same particle. In order to produce robust nanosensors, a novel conjugation strategy was developed involving a heterofunctional linker capable of rigidly attaching various components to the nanoparticle surface. Since most biomarkers of interest are localized intracellularly, the delivery functionality was a key focus. It was achieved using the TAT-HA2 fusion peptide which has been previously shown to enhance both endosomal uptake and subsequent release into the cytosol. The feasibility of these nanoparticles as intracellular sensors was proposed by attempting to image actin rearrangement in live fibroblasts. The assembly of nanoparticles at the leading of motile cells was which was potentially due to actin targeting resulted in a red shift in scattering maxima due to plasmon resonance coupling between particles as well as a dramatic increase in scattering intensity. Although several challenges still exist, the potential for these contrast agents as nanosensors for the presence of proteins implicated in viral carcinogenesis is also introduced.Item Simple and inexpensive biosensors for point-of-care diagnostics(2012-12) Liu, Hong, active 2012; Crooks, Richard M. (Richard McConnell)In this dissertation, three types of paper-based analytical devices for point-of-care biosensing, a potentiometric method for analyzing percent hemoglobin A1c (%HbA1c) and a PDMS-glass microelectrochemical device for highly reproducible amperometric measurement in microdroplet, are described. The first paper-based sensing device is fabricated using the principles of origami (paper folding). The three-dimensional origami paper analytical device (oPAD) is fabricated on a single sheet of flat paper in a single photolithographic step and assembled by simply folding the paper by hand. Following analysis, the device can be unfolded to reveal each layer for optical and fluorescent read-out. The second type of paper-based device has an integral aluminum/air battery as the power source and reports its output using Prussian blue as an electrochromic indicator. The integrated aluminum/air battery powers both the electrochemical sensor and the electrochromic read-out. The applicability of the device to point-of-care sensing is demonstrated by qualitative detection of glucose and H2O2 in artificial urine. The third type of paper-based device (oPAD 2) uses an aptamer to recognize the analyte, adenosine, a glucose oxidase tag to modify the relative concentrations of an electroactive redox couple, and a digital multimeter to transduce the result of the assay. Adenosine is quantitatively determined using this device with a detection limit of 11.8 uM. The method for measuring HbA1c concentration, hemoglobin concentration, and thus %HbA1c in human blood is based on potentiometry. We use Alizarin red s (ARS) as a redox indicator. The potential shift of ARS owing to diol-boronic acid complexation is used to determine the HbA1c, which is a competitor of ARS for the complexation reaction. The concentration of Hb is determined by reacting it with Fe(CN)₆³⁻ and measuring the potential shift arising from the reduction of Fe(CN)₆³⁻ by Hb. The results obtained for %HBA1c in human blood are in good agreement with those determined using a reference method. The method for highly reproducible chronoamperometric analysis of the contents of microdroplets is developed. Aqueous microdroplets (~ 1 nL) and separated by a fluorocarbon solvent are generated within a microfluidic device using a T-shaped junction. Highly reproducible quasi-steady-state currents (relative standard deviations = ~ 2%) are observed when the microdroplets are stretched by a factor of 10 in a narrowed segment of a microchannel, which leads to desirable intradroplet mass transfer characteristics. Importantly, the design of the microelectrochemical device ensures direct contact between intradroplet redox molecules and the electrode surface to study inner-sphere electrocatalytic processes such as the oxygen reduction reaction. Finite-element simulations are presented that are in accord with the experimental findings.Item WiFi-Med : implementation of a ubiquitous health monitoring system on an Android platform(2011-08) Qamar, Nabil; Perry, Dewayne E.; Aziz, AdnanRecent technological advances in biosensors, wireless networking, and mobile computing have enabled the design of systems which are capable of autonomously monitoring various vital signs and providing personalized feedback (e.g. alerts, alarms, and triggers) for the user in real-time. As technology advances, there is no doubt that quality of life will improve for patients and the medical world alike. This thesis describes WiFi-Med, a client side, mobile application built on the Android platform. Our project is designed to enable a mobile device user to aggregate and monitor physiological data through wireless biosensors. Currently, our focus is to develop and improve an Android application by using simulated physiological data. Once perfected, WiFi-Med application can be easily integrated with a body sensor network. First, we present the motivation behind WiFi-Med through real life user scenarios, followed by an introduction to the Android platform architecture. Next, we describe application design and architecture, implementation model and test strategy. Finally, we conclude with a discussion of future development ideas and present our thoughts on prospects of collaborating WiFi-Med and biosensors in ubiquitous computing environments.