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Lead (Pb) levels in tap water below the established water safety guideline are now considered harmful, thus detecting sub-parts-per-billion level Pb is important. This thesis reports on a miniaturized Copper (Cu)−based electrochemical sensor fabricated from thick film electrodes for their superior sensing performance. These thick film electrodes are based on highly conductive rolled-annealed Cu foil that has a compact bulk structure, but these advantages are often offset by the fact that RA Cu foil is difficult to bond to a substrate due to poor film-adhesion property and lack of mechanical interlocks. For this reason, we develop a direct bonding process for Cu/polymer. An integrated three-electrode planar configuration is then fabricated on the bonded specimen to achieve a fully-functional sensor that can detect 0.2 μg/L (0.2 ppb) Pb2+ ions from a 100 μL sample in only 30 s. This is the most rapid detection of Pb featured to date by an all Cu-based sensor. This thesis first focuses on improving substrate adhesion of RA Cu foil to liquid crystal polymer (LCP). This is achieved by a surface activated bonding process where Cu and LCP surfaces are treated with low-power reactive ion etching oxygen plasma followed by low-pressure contact at 230 °C. This treatment produces hydroxyl (OH−) groups on Cu and LCP surfaces making them highly hydrophilic. When Cu and LCP are contacted and heated, the OH− chains condense by dehydration and form an intermediate oxide layer. This layer mainly develops as Cu2O nanoparticles from the plasma-treated Cu side due to thermal oxidation in air. These nanoparticles diffuse into the polymer substrate when heated under mechanical pressure, resulting in a strongly bonded flexible specimen for the sensor. A simple, inexpensive, and production-friendly fabrication process is then developed for these sensors. Following direct bonding, flexible Cu/LCP is fed into a LaserJet printer for a one-step transfer of polyester resin−based electrode mask on Cu. This is followed by etching, packaging, and a chlorinating process to achieve a fully-functional integrated sensor. The sensing performance of directly bonded Cu/LCP is comparable to that of commercially available Cu/polyimide (PI) laminate. Our approach holds promise towards realizing low-cost integrated water quality monitoring systems. / Thesis / Master of Applied Science (MASc) / Lead contamination in tap water has major health risks for which monitoring of its levels is important. In this thesis, we develop a low-cost copper/polymer-based lead sensor. The sensor is fabricated from high-quality metal foil electrodes that are integrated to a polymer substrate by a direct bonding process. This enables strong adhesion of foil-based electrodes to the substrate that is crucial to the sensor performance and packaging integrity. We investigate the bonding mechanism between copper and polymer to understand the fundamentals of materials integration. These findings will lead to the development of polymer-based sensors and integrated systems. The bonded sensor bases are mechanically flexible, which facilitates a rapid and low-cost fabrication process using a laser printer. The developed sensor has a fast response time (30 s) and can detect very low levels of lead, thus making it suitable for water quality monitoring applications in under-developed and developed countries with legacy water systems that have not been upgraded yet.

Nerve agents are acetylcholinesterase inhibitors and among the most toxic chemical warfare agents ever synthesized. Detection of these chemicals is critical for the protection of populations and strategic resources. G-series nerve agents are volatile compounds. V-series nerve agents are persistent phosphonothioate compounds. Persistent nerve agents do not readily volatilize and can contaminate environmental resources for extended periods. While nerve agents are inherently non-electroactive, they can be hydrolyzed to electroactive products compatible with electrochemical sensing. Zr(IV) MOFs are next-generation nanoporous materials, which have been shown to rapidly catalyze nerve agent hydrolysis. In this work, the catalytic processes of MOF-808, a specific Zr(IV) MOF, towards nerve agents are leveraged to develop novel Zr(IV) MOF-enabled electrochemical sensors capable of sensitively detecting both G-series and V-series nerve agents. Initially, a Zr(IV) MOF-enabled potentiometric sensor was developed for G-series nerve agent detection. The potentiometric sensor was tested using G-series nerve agent simulants, dimethyl methylphosphonate (DMMP) and diisopropyl fluorophosphate (DIFP). The potentiometric sensor had a limit-of-detection (LOD) of 185 and 20 µM for DMMP and DIFP, respectively. Following the potentiometric sensor, a Zr(IV) MOF-enabled voltammetric sensing strategy using sequential hydrolysis and detection for low-concentration detection of V-series nerve agents was developed. The full range of operation for the V-series nerve agent sensor was demonstrated using MOF-808 and a V-series nerve agent simulant, demeton-S methylsulphon (DMTS). MOF-808 was shown to rapidly, selectively, and completely hydrolyze DMTS into electroactive products. A LOD of 30 nM for DMTS was measured for this preliminary sensor. A sensor platform was developed to improve sensor applicability with smaller sample sizes and concurrent hydrolysis and detection. Furthermore, various alkaline buffers were studied to minimize background currents. The response of the developed sensor was evaluated for both DMTS and VX and demonstrated an LOD of 4 µM and 10 µM, respectively. The sensor also detected the presence of DMTS and VX from environmental samples in a simulated warfare scenario. This work demonstrates the feasibility of sensitive, rapid, and robust electrochemical sensing of both G-series and V-series nerve agents for in-field applications.

The use of graphene and conductive polyaniline nanomaterials in the field of electrochemistry is increasing due to their excellent conductivity, rapid electron transfer and high specific surface area. However, these properties are strongly dependent on the preparation processes. To accelerate the development of advanced electrochemical sensors for the simultaneous detection of trace amounts of heavy metal ions, two facile and green methods are proposed to improve their performance in this thesis. The first one was dedicated to make graphene-carbon nanotube hybrid nanocomposites. The introduction of carbon nanotubes not only greatly enhances the conductivity of graphene but also suppresses, to some degree, the aggregation between graphene nanosheets. Another method proposed in this thesis work was to synthesize a phytic acid doped polyaniline nanofiber based nanocomposite. The synergistic contribution from polyaniline nanofibers and phytic acid enhances the accumulation efficiency and the charge transfer rate of metal ions during the differential pulse anodic stripping voltammetry analysis. The above-mentioned nanocomposite modified electrodes were all successfully applied to real samples for the simultaneous detection of Cd2+ and Pb2+ with good recovery rates. Meanwhile, corrosion protection is another important branch in the field of electrochemistry. In this direction, an active alkyd-polyaniline composite coating with self-healing functionality was prepared. The polyaniline used in this thesis was doped with p-toluene sulfonic acid, which was employed to increase the conductivity of polyaniline, and 1 wt.% of as-prepared polyaniline nanoparticles were found to offer an effective conductive network for anticorrosion. Finally, the reasons that such low loading levels of nanomaterials can result in significantly reinforced properties in nanocomposites were studied with combined atomic force microscopy (AFM) techniques. The results demonstrated that the interphase for a 40-nm-sized silica particle could extend to 55–70 nm in poly(ethyl methacrylate) (PEMA) and poly(isobutyl methacrylate) (PiBMA) polymer matrix, and the interphase exhibited a gradient distribution in surface nanomechanical properties. / <p>QC 20170315</p>

Para o desenvolvimento dos sensores aqui descritos foram utilizados materiais inovadores considerando relatos atuais da literatura, materiais estes: óxido de grafeno, óxido de grafeno reduzido, nanocompósitos de grafeno e nanopartículas (ródio, antimônio e sílica mesoporosa desordenada), materiais híbridos a base de grafeno e quantum dots de CdTe, além de biossensores incorporando a enzima lacase. Estes materiais foram sintetizados utilizando metodologias específicas e caracterizados por diversas técnicas analíticas como microscopia eletrônica de transmissão de alta resolução, microscopia de força atômica, espectroscopia Raman, difração de raios-X, espectroscopias de UV-Vis e fotoluminescência, e técnicas eletroquímicas. Posteriormente, os materiais foram utilizados para modificação em eletrodos de carbono vítreo e utilizados na determinação de interferentes endócrinos (os hormônios estriol e 17&beta;-estradiol) como sensores eletroquímicos em amostras ambientais e clínicas. Em essência, os eletrodos desenvolvidos apresentaram importantes vantagens, tais como alta sensibilidade, boa reprodutibilidade, simples instrumentação, fácil preparação e procedimentos analíticos rápidos, apresentando baixos limites de detecção, na ordem de picomolar e nanomolar, com baixa taxa de interferência de outras espécies na mesma matriz da amostra. Concluindo assim que as técnicas eletroquímicas podem ser facilmente aplicadas na determinação de interferentes endócrinos em amostras reais. / For the development of the sensors described here innovators materials were used considering current literature reports, these materials: Graphene oxide, reduced graphene oxide, nanocomposites graphene and nanoparticles (rhodium and antimony), hybrid materials of graphene and CdTe quantum dots, and biosensors incorporating the laccase enzyme. These materials were synthesized using specific methodologies and characterized by several analytical techniques such as transmission electron microscopy, high resolution transmission electron microscopy, atomic force microscopy, Raman spectroscopy, X-ray diffraction, UV-Vis and photoluminescence spectroscopy and electrochemical techniques. Subsequently, the materials were used for modification of glassy carbon electrodes to the determination of endocrine disruptors (estriol and 17&beta;-estradiol hormone) as electrochemical sensors for environmental and clinical samples. In essence, developed electrodes showed important advantages such as high sensitivity, good reproducibility, simple instrumentation, easy preparation and quick analytical procedures, with low detection limits in the range of picomolar and nanomolar, low interference rate of other species in same matrix sample. Finally, electrochemical techniques can be easily applied in the determination of endocrine disruptors in real samples.