ECE Theses and Dissertations

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Browsing ECE Theses and Dissertations by Subject "Analytical chemistry"

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    Laser spectroscopic trace chemical sensors for environmental sensor networks and portable medical devices
    (2008) So, Stephen G.; Tittel, Frank K.
    This thesis represents the development of the first laser spectroscopy based trace-gas sensors with sensor characteristics which simultaneously satisfy low cost, handheld footprint, low power, and long term autonomous operation while still providing part-per-billion detection sensitivity and negligible interference to enable trace gas sensor networks and wearable sensors. In order to realize these demanding criteria, this work describes the development of a complete laser spectroscopic sensor platform from the ground up to determine all of the tradeoffs inherent to photonic chemical sensing, and presents a sensor platform with a configuration to meet as many application requirements as possible. Specifically, complete photonic sensor integration and design optimization (e.g. digital signal processing, low power analog, digital control technology, high speed digital design, efficient programming, infrared laser technology, mechanical design) provides sensor characteristics which are significantly improved over the current sensor technology. These sensors can permit the portable deployment of trace gas sensors and enable applications previously unattainable with any other gas sensing method. A performance comparison of the various different types of sensors measured according to these new metrics of cost, size, power consumption in addition to standard metrics (such as sensitivity and specificity) will provide a complete description of advantages and disadvantages of each trace gas sensing technique. Performance characteristics of an open-access handheld sensor platform also provide the baseline for comparison in terms of all of these new criteria. This work will also detail the development path of each major sensor component to allow new technologies to update the original modules. This thesis also describes a scalable network of high sensitivity trace gas sensors, something which has not been achieved to-date. Additionally, issues such as variable-power consumption sensor management and gas sensor data harvesting and analysis will be addressed. Several new applications will be described which may be performed with the optimized sensors which were difficult to perform previously. Finally, this thesis will extrapolate future optimal sensor configurations based on current research in MEMS, photonics, networking, integration, and sensing and will conclude with a discussion of the impact of the various advances achieved in this work.
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    Profiling the near field of nanoshells using surface enhanced Raman spectroscopy and fluorescence spectroscopy
    (2006) Lal, Surbhi; Halas, Naomi J.
    Plasmon resonances in metal nanoparticles control the far field and near field optical properties of these metallic structures. The enhanced electromagnetic near field is strongest at the surface of the nanoparticles and rapidly decays away from the surface. This enhanced near field is exploited in surface enhanced spectroscopies including Surface Enhanced Raman Spectroscopy (SERS) and Metal Enhanced Fluorescence Spectroscopy (MEFS). A measurement of the decay profile of the fringing field is important both for further development of surface enhanced spectroscopy for sensor device application, and for understanding from a fundamental physics point of view. Gold nanoshells are spherical colloidal nanoparticles with a silica core covered by a thin gold shell. The plasmon resonance of nanoshells can be controllably tuned in the visible and infrared parts of the spectrum. The near field profile of nanoshells can be theoretically calculated on the basis of Mie scattering theory. The thesis describes a series of experiments designed to experimentally verify the near field profile of nanoshells. A scaffold of ss-DNA is used to place a fluorescein dye molecule at varying distances from the nanoshell surface. The SERS intensity from both the scaffold molecules and the fluorescein placed at the end of the tether is measured simultaneously and self consistently. The fluorescein-ss-DNA nanoshell conjugate structures are also used to study the distance dependence of the fluorescence emission from fluorescein. The thesis discusses the results of the SERS intensity profile agreement with the intensity profile calculated using Mie scattering theory. The quenching and enhancement of the fluorescence emission at varying distances from the nanoshell surface are also discussed.