abstract: Tin (Sn) has a high-specific capacity (993 mAhg-1) as an anode material for Li-ion batteries. To overcome the poor cycling performance issue caused by its large volume expansion and pulverization during the charging and discharging process, many researchers put efforts into it. Most of the strategies are through nanostructured material design and introducing conductive polymer binders that serve as matrix of the active material in anode. This thesis aims for developing a novel method for preparing the anode to improve the capacity retention rate. This would require the anode to have high electrical conductivity, high ionic conductivity, and good mechanical properties, especially elasticity. Here the incorporation of a conducting polymer and a conductive hydrogel in Sn-based anodes using a one-step electrochemical deposition via a 3-electrode cell method is reported: the Sn particles and conductive component can be electrochemically synthesized and simultaneously deposited into a hybrid thin film onto the working electrode directly forming the anode. A well-defined three dimensional network structure consisting of Sn nanoparticles coated by conducting polymers is achieved. Such a conductive polymer-hydrogel network has multiple advantageous features: meshporous polymeric structure can offer the pathway for lithium ion transfer between the anode and electrolyte; the continuous electrically conductive polypyrrole network, with the electrostatic interaction with elastic, porous hydrogel, poly (2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylonitrile) (PAMPS) as both the crosslinker and doping anion for polypyrrole (PPy) can decrease the volume expansion by creating porous scaffold and softening the system itself. Furthermore, by increasing the amount of PAMPS and creating an interval can improve the cycling performance, resulting in improved capacity retention about 80% after 20 cycles, compared with only 54% of that of the control sample without PAMPS. The cycle is performed under current of 0.1 C. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2015

A urease (Canavalia ensiformis DC.) foi fisicamente imobilizada em matrizes de polipirrol (PPI) com o objetivo de se detectar uréia em amostras padrão. A eletropolimerização do pirrol foi realizada por voltametria cíclica em uma faixa de potencial de -1,0 a 1,0 V vs. ECS em um meio aquoso contendo 0,2 mol/L de \'LI\'CL\'O IND.4\' e 0,1 mol/L de pirrol. Este procedimento permitiu também a imobilização da enzima na matriz polimérica em suas formas, urease purificada (comercial) e como extrato bruto obtido a partir do feijão de porco (Jack Bean), após a adição de 300 \'mü\'g/mL de urease purificada ou 100 \'mü\'L de extrato bruto de feijão de porco. A urease purificada possui 34.375 U/g de sólido e o extrato bruto, 13.000 UA/mL, valores obtidos por titrimetria. A presença da enzima imobilizada nos filmes de PPI foi verificada por voltametria cíclica, FTIR, microscopia eletrônica de varredura (MEV), microscopia de força atômica (AFM) e por uma microbalança de cristal de quartzo (MCQE). A atividade da enzima após a imobilização nos filmes de PPI foi confirmada pela presença de íons amônio em solução, que são formados como produtos da reação de hidrólise da uréia catalisada pela enzima. Como o transdutor influencia a eficiência e a sensibilidade do biossensor, dois métodos de transdução foram estudados: cronoamperometria, aplicando-se um potencial de -0,28 V durante 120 s em tampão fosfato pH 7,0 e a cronopotenciometria, aplicando-se uma corrente de 1,0 mA durante 120 s em tampão fosfato pH 7,0 variando-se a concentração de uréia. O principal objetivo deste trabalho foi avaliar a eficiência do biossensores para a detecção de uréia por meio de transdutores potenciométricos e amperométricos e depois comparar as eficiências dos filmes de PPI/urease purificada e PPI/extrato bruto como biosensores. / Urease (Canavalia ensiformis DC.) was physically immobilized on polypyrrole (PPy) films aiming at detecting urea in standard samples. The electropolymerization of pyrrole was performed by cyclic voltammetry at a potential range from -1.0 to 1.0 V vs SCE in an aqueous medium containing \'LI\'CL\'O IND.4\' 0.2 mol/L and 0.1 mol/L pyrrole. This procedure also allowed us to immobilize the enzyme into the PPy matrix in forms, commercially purified and crude extract of urease obtained from Jack Bean (Canavalia ensiformis) after adding into the electropolymerization media 300 \'mü\'g/mL of purified urease or 100 \'mü\'L of crude extract. The urease solutions had units of active enzyme of 34.375 U/g (purified) and 13.000 UA/mL (crude extract), and the crude extract was obtained from Jack beans by titrimétric methods. The presence of urease immobilized into the PPy film was verified by cyclic voltammetry, FTIR, scanning electron microscopy (SEM), atomic force microscopy (AFM), and by electrochemical quartz crystal microbalance (EQCM) The activity of the enzyme after immobilizing into the PPy films was confirmed by the presence of ammonium ions in solution, since they are formed as catalytic products by urea hydrolysis reaction catalyzed enzyme. The transducer element influences the efficiency and sensitivity of the biosensor, and two transducer methods were studied: chronoamperometry, by applying a potential of -0.28 V during 120 s in buffer phosphate at pH 7.0 and chronopotentiometry, by applying a current of 1.0 mA during 120 s in buffer phosphate at pH 7.0 both after varying the urea concentration. Our main purpose was to evaluate the efficiency of the biosensors for detecting urea by means of potentiometric and amperometric transducers and then compare the efficiencies of PPY/purified urease e PPY/crude extract as biosensors.

Thesis advisor: Thomas C. Chiles / Rapid diagnosis of infectious disease at the site of the patient is critical for preventing the escalation of an outbreak into an epidemic. This is particularly true for cholera, a disease known to spread swiftly within resource-limited populations. A device suited to point-of- care (POC) diagnosis of cholera must not only demonstrate laboratory levels of sensitivity and specificity, but it must do so in a highly portable, low-cost manner, with a simplistic readout. Here, we report novel proof-of-concept lab-on-a-chip (LOC) electrochemical immunosensors for the detection of cholera toxin subunit B (CTX), based on two nanostructured architectures: the gold dendritic array, and the extended core coax (ECC). The dendritic array has an ~18x greater surface area than a planar gold counterpart, per electrochemical measurements, allowing for a higher level of diagnostic sensitivity. An electrochemical enzyme-linked immunosorbant assay (ELISA) for CTX performed via differential pulse voltammetry (DPV) on the dendritic sensor demonstrated a limit-of detection of 1 ng/mL, per a signal-to-noise ratio of 2.6, which was more sensitive than a simple planar gold electrode (100 ng/mL). This sensitivity also matches a currently available diagnostic standard, the optical ELISA, but on a miniaturized platform with simple electrical readout. The ECC was optimized and explored, undergoing several changes in design to facilitate sensitive LOC electrochemical detection. The ECC matched the off-chip sensitivity towards CTX demonstrated by a previous non-extended core coaxial iteration, which was comparable to a standard optical ELISA. In contrast to the previous coaxial architecture, the ECC is amenable to functionalization of the gold core, allowing for LOC detection. ECCs were functionalized using a thiolated protein G, and CTX was detected via an electrochemical ELISA. While this work is ongoing, the ECC shows promise as a platform for LOC electrochemical ELISA. The ability to potentially meet POC demands makes biofunctionalized gold dendrites and ECCs promising architectures for further development as LOC sensors for the detection of infectious disease biomarkers. / Thesis (PhD) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.

>Magister Scientiae - MSc / Diabetes, a worldwide disease, is classified into two types, type 1 or insulin-dependent and type 2 or noninsulin-dependent. Based on reports published by the International Diabetes Federation, the total number of those suffering from diabetes is growing every year. Statistics predict that type 2 diabetes, currently affecting about 8% of the adult population, would spread at such a pace that by 2030, more than 40 million cases of diabetes would be found throughout the world. On the other hand, studies revealed that patients with type 2 diabetes mellitus (T2DM) have a lower incidence of tumour development than healthy controls and that patients diagnosed with cancer have a lower risk of mortality when treated with metformin. However, the frequent use of metformin with low oral bioavailability ranging between 40-60% in the intestinal environment leads to large accumulation on the enterocytes. / 2024-02-24

>Magister Scientiae - MSc / Anode catalysts are one of the key components of direct alcohol fuel cells (DAFCs). They play a huge role in the alcohol oxidation reaction (AOR) that occurs on the anode side. Palladium (Pd) supported on carbon material has been reported to have good catalytic activity towards alcohol oxidation reactions. Better stability and activity has been reported for catalysts supported on conductive polymers like polypyrrole (PPy) when compared to traditional carbon support material. This study investigated the effect of support materials on Pd and PdCo electro-catalysts while concurrently determining the support material that can improve the activity and stability of Pd and PdCo electro-catalysts used as direct alcohol fuel cells catalysts. All Pd and PdCo catalysts supported onPPy (prepared using oxidative polymerization method), reduced graphene oxide (rGO) and prepared using modified Hammers method and multi-walled carbon nanotubes and pre-treated by acid. All the catalysts were synthesized using the modified polyol method.

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In this research, different anionic dopants were investigated for the fabrication of polypyrrole (PPy) electrode materials for electrochemical capacitors (ECs). Anionic dopants from catechol, salicylic acid and chromotropic acid family allowed for the formation of adherent PPy thin film on stainless steels current collectors by electropolymerization. Comparison between galvanostatic and pulse electropolymerization of PPy thin films was made. Pulse electropolymerization was found to provide improved impregnation of Ni plaque current collectors and formation of nanostructured coating. The electrodes prepared by pulse electropolymerization showed higher porosity, lower electrical resistance, higher capacitance and improved cyclic stability. In order to overcome the mass loading limitation for thin film PPy electrodes, chemical polymerization of PPy was investigated. The use of fine particles, prepared by the chemical polymerization method, allows impregnation of Ni foams and fabrication of porous electrodes with high materials loading. Moreover, improved capacitive performance and cyclic stability was obtained for PPy electrodes with high materials loading using new anionic dopants. To further improve the cyclic stability of PPy electrodes, multiwalled carbon nanotubes (MWCNT) were used for the fabrication of PPy-MWCNT composite materials due to their high surface area and excellent conductivity. Different dispersants as well as dispersing methods were studied in order to obtain stable MWCNT suspensions. Among those dispersants, multifunctional anionic dopants were found to benefit the formation of MWCNT suspension as well as the polymerization of PPy. A conceptually new approach has been developed for the fabrication of PPy coated MWCNT based on the use of multifunctional anionic dopants. The use of PPy coated MWCNT allowed excellent electrochemical performance for high active mass loadings, required for commercial EC applications. The electrodes and devices made of PPy coated MWCNT showed high capacitance, good capacitance retention at high charge-discharge rates and good cycling stability. The record high capacitance achieved at high charge-discharge rates is promising for the development of high power ECs. / Thesis / Doctor of Philosophy (PhD)

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