Date of Award

Fall 2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

Lee Sawyer

Abstract

Even in modern times, the consumption of polluted water continues to inflict tremendous suffering on millions of people worldwide that is largely preventable with adequate sanitation practices, routine water quality diagnostics, and treatment. However, conventional water quality monitoring practices remain a time consuming endeavor, where water samples collected on-site are transported to off-site laboratories for evaluation with laboratory-scale chemical analysis devices. While considerable efforts have been made to miniaturize these devices for in-field use, many of the devices reported in the literature provide an incomplete assessment of a water contaminant's environmental impact by focusing on identifying its chemical composition and providing limited or no data regarding the contaminant's concentration.

A water contaminant's chemical composition and concentration must be known to adequately assess its human health and environmental impact, as well as coordinating effective restoration and maintenance efforts. The field portable water diagnostic system reported here addresses this need with dual miniaturized plasma spectroscopic and capacitive sensing elements. Both sensing platforms capitalize on a water sample preconcentration stage that isolates contaminant particles from the liquid water solution as a porous thin film. This arrangement yields a more robust spectral emission signature from which the contaminant can be spectroscopically identified and allows the contaminant's concentration to be estimated as a function of the film's capacitance. A numerical contaminant concentration-to-capacitance model was developed for water samples containing single and multiple contaminant species to interpret the capacitive sensor's output, incorporating the physical parameters of the contaminant material and the device's capacitive analysis chamber which houses the porous contaminant film.

Prototypes of each sensing platform were developed separately to investigate first generation design flaws and optimize the spectroscopic and capacitive analysis procedures. Design modifications for each platform a were then incorporated into an integrated diagnostic system, combining both sensing platforms, to perform a complete water quality analysis of a pollutant's chemical composition and concentration. Performance testing of the integrated diagnostic system focused on analyzing representatives of suspended and dissolved water contaminants that promote the incubation and spread of waterborne pathogens at concentration ranges comparable to regulations set by the United States Environmental Protection Agency.

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