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Title:Colorimetric sensor array for identification of fungi & ultrasonic spray synthesis for supercapacitor materials
Author(s):Zhang, Yinan
Director of Research:Suslick, Kenneth S
Doctoral Committee Chair(s):Suslick, Kenneth S
Doctoral Committee Member(s):Sweedler, Jonathan V; Orlean, Peter; Bailey, Ryan C
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Abstract:In this thesis, functional materials synthesis and fabrication is described within the two areas of (1) colorimetric sensor array for identification of fungi, and (2) ultrasonic spray synthesis for supercapacitor electrode materials. Human fungal infections have attracted intense current interest, especially in the light of recent outbreaks from pharmaceutical contamination, but also due to infections of immunocompromised patients by opportunistic fungal strains. Fungi stink: that is to say, they produce distinctive volatile organic compounds. The profiles of these VOCs provide a potential diagnostic method that may be able to overcome current limitations in traditional fungal diagnostics. Previous methods for VOC profiling, however, are either costly, non-portable (e.g., GC-MS) or insensitive and intolerant to humidity variation (e.g., electronic noses). In this project, an optoelectronic nose approach was used with our disposable colorimetric sensor array for rapid differentiation and identification of human pathogenic fungi based on their smell (i.e., the volatiles that they produce). Twelve clinically relevant fungal strains gave unique sensor array responses and were correctly clustered using hierarchical cluster analysis within 3 hours, which is a clinically relevant time frame. Classification prediction accuracy was 94%, based on standard jackknifed linear discriminant analysis. We also introduce the application of a cutting-edge statistical method, tensor discriminant analysis, which takes advantage of the high dimensionality of our sensor array data, giving a prediction accuracy of 98.1%. Furthermore, we have shown that our sensor array has great potential for rapid screening the effects of anti-fungal drugs on particular fungal strains. This is the first example of colorimetric volatile profiling for fungal strain identification. Compared to single-data-point analysis methods, this inexpensive technique (~$3 for each test kit using an ordinary flatbed scanner) allows for real-time identification of fungi in culture. We expect this is the first step in the development of a rapid, facile, and low-cost tool for diagnosis of fungal infections with potential additional applications for environmental monitoring (e.g., “sick-building syndrome”). Conjugated polymers have been intensively investigated as electrode materials for supercapacitors because of their excellent electrochemical reversibility, fast switching between redox states, high conductivity in a doped state, mechanical flexibility, and low cost. Among them, poly(3,4-ethylenedioxythiophene) (PEDOT) is especially attractive due to its high stability and low toxicity. Prior PEDOT materials are generally synthesized with surfactants or template methods so as to achieve nano- or micro-structures with high surface area and to maximize capacitance at high charge and discharge rates. These synthesis methods, however, are generally cumbersome (multiple steps) or expensive (such as nano-structured sacrificial templates), and can easily introduce impurities that negatively affect the electrochemical properties of the PEDOT products. In this project, we used ultrasonic spray polymerization (USPo) method for facile and continuous PEDOT microsphere synthesis without the addition of templates or surfactants. During this USPo process, PEDOT is synthesized by polymerization of the monomer 3,4-ethylenedioxythiophene in the precursor solution in micron-sized droplets that are generated during ultrasonic nebulization. Here, three types of morphologies (solid, porous, and hollow) are synthesized by simply controlling oxidants and precursor solvents. Supercapacitor behavior is characterized and determined to be as high as 160 F/g (Farad/gram), which is the highest of reported PEDOT microspheres. Moreover, taking advantage of the USPo setup, we also demonstrate an innovative spray coating method as a useful electrode fabrication process. This is the first synthetic route to provide PEDOT microsphere production with controllable morphologies, and it does not require additional stabilizing agents or sacrificial templates. In addition, it also covers a little-investigated area of ultrasonic spray techniques for polymer microsphere synthesis. The potential impact of a facile, cost-effective, and scalable synthetic method for PEDOT supercapacitor materials makes our approach significant to the field of energy storage materials as well as more generalized microsphere materials synthesis. The second example of using an ultrasonic spray technique is in the synthesis of manganese oxide (MnO2) microspheres. In this case, a mixed solution of potassium permanganate and hydrochloric acid was nebulized into micro-sized droplets, which were then carried by air flow through a furnace tube. Each micro-droplet serves as one micro-reactor and produces one microsphere. Upon heating, KMnO4 was decomposed into MnO2 microspheres; this synthetic process can easily be scaled up. Characterization of the MnO2 microspheres by SEM, TEM, powder XRD, Raman Spectroscopy, and XPS is described. Different morphologies of MnO2 microspheres could be controlled by tuning the precursor concentrations (and ratios) and furnace temperatures; for example, microspheres synthesized at 150 °C gave polycrystalline MnO2 while synthesis at 500 °C yielded needle-shape α-MnO2 crystals. The electrochemical properties investigated by cyclic voltammetry gave specific capacitance as high as 320 F/g, demonstrating promising properties as supercapacitors. In addition, these microspheres can be directly sprayed on conductive substrates, such as carbon fiber paper, and may have useful applications as a supercapacitor electrode coating. The supercapacitive properties of MnO2 microspheres at higher charge and discharge rates can be improved by increasing the surface area coverage or coating them with a thin layer of conductive polymer.
Issue Date:2015-11-18
Rights Information:Copyright 2015 Yinan Zhang
Date Available in IDEALS:2016-03-08
Date Deposited:2015-12

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