Matching Items (126)
Description
Demand for biosensor research applications is growing steadily. According to a new report by Frost & Sullivan, the biosensor market is expected to reach $14.42 billion by 2016. Clinical diagnostic applications continue to be the largest market for biosensors, and this demand is likely to continue through 2016 and beyond. Biosensor technology for use in clinical diagnostics, however, requires translational research that moves bench science and theoretical knowledge toward marketable products. Despite the high volume of academic research to date, only a handful of biomedical devices have become viable commercial applications. Academic research must increase its focus on practical uses for biosensors. This dissertation is an example of this increased focus, and discusses work to advance microfluidic-based protein biosensor technologies for practical use in clinical diagnostics. Four areas of work are discussed: The first involved work to develop reusable/reconfigurable biosensors that are useful in applications like biochemical science and analytical chemistry that require detailed sensor calibration. This work resulted in a prototype sensor and an in-situ electrochemical surface regeneration technique that can be used to produce microfluidic-based reusable biosensors. The second area of work looked at non-specific adsorption (NSA) of biomolecules, which is a persistent challenge in conventional microfluidic biosensors. The results of this work produced design methods that reduce the NSA. The third area of work involved a novel microfluidic sensing platform that was designed to detect target biomarkers using competitive protein adsorption. This technique uses physical adsorption of proteins to a surface rather than complex and time-consuming immobilization procedures. This method enabled us to selectively detect a thyroid cancer biomarker, thyroglobulin, in a controlled-proteins cocktail and a cardiovascular biomarker, fibrinogen, in undiluted human serum. The fourth area of work involved expanding the technique to produce a unique protein identification method; Pattern-recognition. A sample mixture of proteins generates a distinctive composite pattern upon interaction with a sensing platform consisting of multiple surfaces whereby each surface consists of a distinct type of protein pre-adsorbed on the surface. The utility of the "pattern-recognition" sensing mechanism was then verified via recognition of a particular biomarker, C-reactive protein, in the cocktail sample mixture.
ContributorsChoi, Seokheun (Author) / Chae, Junseok (Thesis advisor) / Tao, Nongjian (Committee member) / Yu, Hongyu (Committee member) / Forzani, Erica (Committee member) / Arizona State University (Publisher)
Created2011
Description
A wireless hybrid device for detecting volatile organic compounds (VOCs) has been developed. The device combines a highly selective and sensitive tuning-fork based detector with a pre-concentrator and a separation column. The selectivity and sensitivity of the tuning-fork based detector is optimized for discrimination and quantification of benzene, toluene, ethylbenzene, and xylenes (BTEX) via a homemade molecular imprinted polymer, and a specific detection and control circuit. The device is a wireless, portable, battery-powered, and cell-phone operated device. The device has been calibrated and validated in the laboratory and using selected ion flow tube mass spectrometry (SFIT-MS). The capability and robustness are also demonstrated in some field tests. It provides rapid and reliable detection of BTEX in real samples, including challenging high concentrations of interferents, and it is suitable for occupational, environmental health and epidemiological applications.
ContributorsChen, Zheng (Author) / Tao, Nongjian (Thesis advisor) / Chae, Junseok (Committee member) / Forzani, Erica (Committee member) / Arizona State University (Publisher)
Created2011
Description
Psychology of justice research has demonstrated that individuals are concerned with both the process and the outcomes of a decision-making event. While the literature has demonstrated the importance of formal and informal aspects of procedural justice and the relevancy of moral values, the present study focuses on introducing a new form of justice: Substantive justice. Substantive justice focuses on how the legal system uses laws to constrain and direct human behavior, specifically focusing on the function and the structure of a law. The psychology of justice literature is missing the vital distinction between laws whose function is to create social opportunities versus threats and between laws structured concretely versus abstractly. In the present experiment, we found that participant evaluations of the fairness of the law, the outcome, and the decision-maker all varied depending on the function and structure of the law used as well as the outcome produced. Specifically, when considering adverse outcomes, individuals perceived laws whose function is to create liability (threats) as being fairer when structured as standards (abstract guidelines) rather than rules (concrete guidelines); however, the opposite is true when considering laws whose function is to create eligibility (opportunities). In juxtaposition, when receiving a favorable outcome, individuals perceived laws whose function is to create liability (threats) as being fairer when defined as rules (concrete guidelines) rather than standards (abstract guidelines).
ContributorsLovis-McMahon, David (Author) / Schweitzer, Nicholas J. (Thesis advisor) / Saks, Michael (Thesis advisor) / Kwan, Sau (Committee member) / Arizona State University (Publisher)
Created2011
Description
This thesis describes several approaches to next generation DNA sequencing via tunneling current method based on a Scanning Tunneling Microscope system. In chapters 5 and 6, preliminary results have shown that DNA bases could be identified by their characteristic tunneling signals. Measurements taken in aqueous buffered solution showed that single base resolution could be achieved with economic setups. In chapter 7, it is illustrated that some ongoing measurements are indicating the sequence readout by making linear scan on a piece of short DNA oligomer. However, to overcome the difficulties of controlling DNA especially ssDNA movement, it is much better to have the tunneling measurement incorporated onto a robust nanopore device to realize sequential reading of the DNA sequence while it is being translocated.
ContributorsHuang, Shuo (Author) / Lindsay, Stuart (Thesis advisor) / Sankey, Otto (Committee member) / Tao, Nongjian (Committee member) / Drucker, Jeff (Committee member) / Ros, Robert (Committee member) / Arizona State University (Publisher)
Created2011
Description
Dual-wavelength laser sources have various existing and potential applications in wavelength division multiplexing, differential techniques in spectroscopy for chemical sensing, multiple-wavelength interferometry, terahertz-wave generation, microelectromechanical systems, and microfluidic lab-on-chip systems. In the drive for ever smaller and increasingly mobile electronic devices, dual-wavelength coherent light output from a single semiconductor laser diode would enable further advances and deployment of these technologies. The output of conventional laser diodes is however limited to a single wavelength band with a few subsequent lasing modes depending on the device design. This thesis investigates a novel semiconductor laser device design with a single cavity waveguide capable of dual-wavelength laser output with large spectral separation. The novel dual-wavelength semiconductor laser diode uses two shorter- and longer-wavelength active regions that have separate electron and hole quasi-Fermi energy levels and carrier distributions. The shorter-wavelength active region is based on electrical injection as in conventional laser diodes, and the longer-wavelength active region is then pumped optically by the internal optical field of the shorter-wavelength laser mode, resulting in stable dual-wavelength laser emission at two different wavelengths quite far apart. Different designs of the device are studied using a theoretical model developed in this work to describe the internal optical pumping scheme. The carrier transport and separation of the quasi-Fermi distributions are then modeled using a software package that solves Poisson's equation and the continuity equations to simulate semiconductor devices. Three different designs are grown using molecular beam epitaxy, and broad-area-contact laser diodes are processed using conventional methods. The modeling and experimental results of the first generation design indicate that the optical confinement factor of the longer-wavelength active region is a critical element in realizing dual-wavelength laser output. The modeling predicts lower laser thresholds for the second and third generation designs; however, the experimental results of the second and third generation devices confirm challenges related to the epitaxial growth of the structures in eventually demonstrating dual-wavelength laser output.
ContributorsGreen, Benjamin C (Author) / Zhang, Yong-Hang (Thesis advisor) / Ning, Cun-Zheng (Committee member) / Tao, Nongjian (Committee member) / Roedel, Ronald J (Committee member) / Arizona State University (Publisher)
Created2011
Description
In the present research, two interventions were developed to increase sun protection in young women. The purpose of the study was to compare the effects of intervention content eliciting strong emotional responses to visual images depicting photoaging and skin cancer, specifically fear and disgust, coupled with a message of self-efficacy and benefits of sun protection (the F intervention) with an intervention that did not contain an emotional arousal component (the E intervention). Further, these two intervention conditions were compared to a control condition that contained an emotional arousal component that elicited emotion unrelated to the threat of skin cancer or photoaging (the C control condition). A longitudinal study design was employed, to examine the effects of condition immediately following the intervention, and to examine sun protection behavior 2 weeks after the intervention. A total of 352 undergraduate women at Arizona State University were randomly assigned to one of the three conditions (F n = 148, E n = 73, C n = 131). Several psychosocial constructs, including benefits of sun protection, susceptibility to and severity of photoaging and sun exposure, self-efficacy beliefs of making sun protection a daily habit, and barriers to sun protection were measured before and immediately following the intervention. Sun protection behavior was measured two weeks later. Those in the full intervention reported higher self-efficacy and severity of photoaging at immediate posttest than those in the efficacy only and control conditions. The fit of several path models was tested to explore underlying mechanisms by which the intervention affected sun protection behavior. Experienced emotion, specifically fear and disgust, predicted susceptibility and severity, which in turn predicted anticipated regret of failing to use sun protection. The relationship between this overall threat component (experienced emotion, susceptibility, severity, and anticipated regret) and intentions to engage in sun protection behavior was mediated by benefits. The present research provided evidence of the effectiveness of threat specific emotional arousal coupled with a self-efficacy and benefits message in interventions to increase sun protection. Further, this research provided additional support for the inclusion of both experienced and anticipated emotion in models of health behavior.
ContributorsMoser, Stephanie E (Author) / Aiken, Leona S. (Thesis advisor) / Shiota, Michelle N. (Committee member) / Kwan, Sau (Committee member) / Castro, Felipe (Committee member) / Arizona State University (Publisher)
Created2011
Description
Nanofluidic devices in which one single-walled carbon nanotube (SWCNT) spans a barrier between two fluid reservoirs were constructed, enabling direct electrical measurement of the transport of ions and molecules. Ion current through these devices is about 2 orders of magnitude larger than that predicted from the bulk resistivity of the electrolyte. Electroosmosis drives excess current, carried by cations, and is found to be the origin of giant ionic current through SWCNT as shown by building an ionic field-effect transistor with a gate electrode embedded in the fluid barrier. Wetting of inside of the semi-conducting SWCNT by water showed the change of its electronic property, turning the electronic SWCNT field-effect transistor to "on" state. These findings provide a new method to investigate and control the ion and molecule behavior at nanoscale.
ContributorsPang, Pei (Author) / Lindsay, Stuart (Thesis advisor) / Ros, Robert (Committee member) / Shumway, John (Committee member) / Tao, Nongjian (Committee member) / Menéndez, Jose (Committee member) / Arizona State University (Publisher)
Created2011
Description
In this project, a novel method is presented for measuring the resistivity of nanoscale metallic conductors (nanowires) using a variable-spacing 2-point method with a modified ultrahigh vacuum scanning tunneling microscope. An auxiliary field emission imaging method that allows for scanning insulating surfaces using a large gap distance (20nm) is also presented. Using these methods, the resistivity of self-assembled endotaxial FeSi2 nanowires (NWs) on Si(110) was measured. The resistivity was found to vary inversely with NW width, being rhoNW = 200 uOhm cm at 12 nm and 300 uOhm cm at 2 nm. The increase at small w is attributed to boundary scattering, and is fit to the Fuchs-Sondheimer model, yielding values of rho0 = 150 uOhm cm and lambda = 2.4 nm, for specularity parameter p = 0.5. These results are attributed to a high concentration of point defects in the FeSi2 structure, with a correspondingly short inelastic electron scattering length. It is remarkable that the defect concentration persists in very small structures, and is not changed by surface oxidation.
ContributorsTobler, Samuel (Author) / Bennett, Peter (Thesis advisor) / McCartney, Martha (Committee member) / Tao, Nongjian (Committee member) / Doak, Bruce (Committee member) / Chen, Tingyong (Committee member) / Arizona State University (Publisher)
Created2011
Description
Obtaining local electrochemical (EC) information is extremely important for understanding basic surface reactions, and for many applications. Scanning electrochemical microscopy (SECM) can obtain local EC information by scanning a microelectrode across the surface. Although powerful, SECM is slow, the scanning microelectrode may perturb reaction and the measured signal decreases with the size of microelectrode. This thesis demonstrates a new imaging technique based on a principle that is completely different from the conventional EC detection technologies. The technique, referred to as plasmonic-based electrochemical imaging (PECI), images local EC current (both faradaic and non-faradaic) without using a scanning microelectrode. Because PECI response is an optical signal originated from surface plasmon resonance (SPR), PECI is fast and non-invasive and its signal is proportional to incident light intensity, thus does not decrease with the area of interest. A complete theory is developed in this thesis work to describe the relationship between EC current and PECI signal. EC current imaging at various fixed potentials and local cyclic voltammetry methods are developed and demonstrated with real samples. Fast imaging rate (up to 100,000 frames per second) with 0.2×3µm spatial resolution and 0.3 pA detection limit have been achieved. Several PECI applications have been developed to demonstrate the unique strengths of the new imaging technology. For example, trace particles in fingerprint is detected by PECI, a capability that cannot be achieved with the conventional EC technologies. Another example is PECI imaging of EC reaction and interfacial impedance of graphene of different thicknesses. In addition, local square wave voltammetry capability is demonstrated and applied to study local catalytic current of platinum nanoparticle microarray. This thesis also describes a related but different research project that develops a new method to measure surface charge densities of SPR sensor chips, and micro- and nano-particles. A third project of this thesis is to develop a method to expand the conventional SPR detection and imaging technology by including a waveguide mode. This innovation creates a sensitive detection of bulk index of refraction, which overcomes the limitation that the conventional SPR can probe only changes near the sensor surface within ~200 nm.
ContributorsShan, Xiaonan (Author) / Tao, Nongjian (Thesis advisor) / Chae, Junseok (Committee member) / Christen, Jennifer Blain (Committee member) / Hayes, Mark (Committee member) / Arizona State University (Publisher)
Created2011
Description
The Beck Depression Inventory II (BDI-II) and the Patient Health Questionnaire 9 (PHQ-9) are highly valid depressive testing tools used to measure the symptom profile of depression globally and in South Asia, respectively (Steer et al., 1998; Kroenke et al, 2001). Even though the South Asian population comprises only 23% of the world’s population, it represents one-fifth of the world’s mental health disorders (Ogbo et al., 2018). Although this population is highly affected by mental disorders, there is a lack of culturally relevant research on specific subsections of the South Asian population.<br/><br/>As such, the goal of this study is to investigate the differences in the symptom profile of depression in native and immigrant South Asian populations. We investigated the role of collective self-esteem and perceived discrimination on mental health. <br/><br/>For the purpose of this study, participants were asked a series of questions about their depressive symptoms, self-esteem and perceived discrimination using various depressive screening measures, a self-esteem scale, and a perceived discrimination scale.<br/><br/>We found that immigrants demonstrated higher depressive symptoms than Native South Asians as immigration was viewed as a stressor. First-generation and second-generation South Asian immigrants identified equally with somatic and psychological symptoms. These symptoms were positively correlated with perceived discrimination, and collective self-esteem was shown to increase the likelihood of these symptoms.<br/><br/>This being said, the results from this study may be generalized only to South Asian immigrants who come from highly educated and high-income households. Since seeking professional help and being aware of one’s mental health is vital for wellbeing, the results from this study may spark the interest in an open communication about mental health within the South Asian immigrant community as well as aid in the restructuring of a highly reliable and valid measurement to be specific to a culture.
ContributorsMurthy, Nithara (Co-author) / Swaminathan, Manasa (Co-author) / Vogel, Joanne (Thesis director) / Kwan, Sau (Committee member) / Department of Psychology (Contributor) / School of Human Evolution & Social Change (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05