This paper describes the development of an electrochemical sensor glassy carbon modified with gold nanoparticles and a film of multiâwalled carbon nanotube and cobalt phthalocyanine (CoPc-fMWCNTs/AuNp/GCE) for the determination of diethylstilbestrol hormone (DES) in water samples and meat, using a square wave technique voltammetry. (SWV). The electrolyte used was Britton-Robinson buffer (BR) 0.04 mol L-1 pH 10.0. Initially it was studied the electrode configuration to be used for the development work, after the optimization of solution pH, study scan speed to evaluate the charge transfer kinetics in the redox process of the DES, the optimized parameters for SWV, the analytical curve, and finally, applying the methodology developed. The optimized parameters for SWV were f = 5 sâ1, a = 50 mV and ΔEs=1 mV. The CoPc-fMWCNTs/AuNp/GCE was ready to be used for the application since all conditions were optimized. Analytical curves were obtained in the concentration ranged from 7.9365 à 10−7 â 5.6604 à 10−6 mol Lâ1 (R = 0.9996) and there were obtained limits of detection (LOD) and quantification (LOQ) of 1.9910 x 10â7 mol Lâ1and 6.6367 x 10â7 mol Lâ1, respectively, being comparable to those reported in the literature. The repeatability and reproducibility of the proposed procedure were evaluated. The relative standard deviation (RSD) were 4.33% and 3.49%, respectively, indicating the precision of the assay. The recovery percentage was 98.56% for the water sample and 94.05% for beef sample (RSD of 0.40 and 1.55% respectively). The modified electrode has developed sensitivity, reproducibility and repeatability appropriate and consistent LOD and LOQ values with those reported in the literature. Moreover, the results obtained by the use of CoPc-fMWCNTs/AuNp/GCE proved very efficient as the detection and DES recovery, being thus a promising device in the detection and quantification of DES in water samples and food. / O presente trabalho descreve o desenvolvimento de um sensor eletroquÃmico de carbono vÃtreo modificado com nanopartÃculas de ouro, nanotubos de carbono de paredes mÃltiplas funcionalizados e ftalocianina de cobalto (CV/NpAu/NTCPMf-FcCo) para a determinaÃÃo do hormÃnio dietilestilbestrol (DES) em amostras de Ãgua e carne, utilizando a tÃcnica de voltametria de onda quadrada (VOQ). O eletrÃlito empregado foi tampÃo BrittonâRobinson (BR) 0,04 mol Lâ1 pH 10,0. Inicialmente estudou-se a configuraÃÃo do eletrodo a ser utilizado para o desenvolvimento do trabalho, depois a otimizaÃÃo do pH do meio, estudo da velocidade de varredura para avaliar a cinÃtica de transferÃncia de carga no processo redox do DES, otimizaÃÃo dos parÃmetros da VOQ, construÃÃo da curva analÃtica e por fim, a aplicaÃÃo da metodologia desenvolvida. Os parÃmetros otimizados para a VOQ foram: f = 5 sâ1, a = 50 mV e ΔEs = 1 mV. De posse de todas as condiÃÃes otimizadas para aplicaÃÃo do CV/NpAu/NTCPMf-FcCo, curvas analÃticas foram obtidas no intervalo de concentraÃÃo de 7,9365 à 10−7 â 5,6604 à 10−6 mol Lâ1 (R = 0,9996) e os limites de detecÃÃo (LD) e de quantificaÃÃo (LQ) calculados foram 1,9910 x 10â7 mol Lâ1 e 6,6367 x 10â7 mol Lâ1, respectivamente, sendo comparÃveis aos citados na literatura. A repetibilidade e a reprodutibilidade do procedimento proposto foram avaliadas. Os valores de desvio padrÃo relativo (DPR) obtidos foram 4,33% e 3,49%, respectivamente, evidenciando a precisÃo da metodologia. O percentual de recuperaÃÃo foi de 98,56% para amostra de Ãgua e 94,05% para amostra de carne bovina (DPR de 0,40 e 1,55% respectivamente). O eletrodo modificado desenvolvido apresentou sensibilidade, reprodutibilidade e repetibilidade adequados, bem como valores de LD e LQ concordantes com os relatados na literatura. Os resultados obtidos pelo emprego do CV/NpAu/NTCPMf-FcCo se mostraram muito eficientes quanto à detecÃÃo e recuperaÃÃo de DES, mostrando-se, desse modo, um dispositivo promissor na detecÃÃo e na quantificaÃÃo de DES em amostras de Ãgua e alimentos.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Nesta Tese apresentamos os estudos de espectroscopia Raman em condiÃÃes extremas de pressÃo hidrostÃtica realizados em nanotubos de carbono de parede dupla (DWCNTs) e tripla (TWCNTs), em dissulfeto de molibdÃnio na forma bulk e em poucas camadas. CÃlculos teÃricos foram usados para dar suporte aos resultados experimentais. Para as amostras de DWCNTs, as mudanÃas no coeficiente de pressÃo da banda G e o desaparecimento dos modos de respiraÃÃo radial (RBMs) entre 2 GPa e 5 GPa foram interpretados como um indicativo do inÃcio e fim do colapso radial dos nanotubos de carbono (CNTs). Os cÃlculos teÃricos usando Tight-Binding baseado no Funcional da Densidade (DFTB) mostraram que a pressÃo de colapso (P_c) para os DWCNTs segue uma lei de potÃncia do tipo d^{-3}_{in}, em excelente acordo com os resultados experimentais. A dependÃncia de P_c em relaÃÃo ao nÃmero de paredes do tubo, como tambÃm a distÃncia inter-paredes tambÃm foram investigadas. Para a amostra contendo TWCNTs, atravÃs da anÃlise dos coeficientes de pressÃo dos modos RBMs em conjunto com o histograma da distribuiÃÃo de diÃmetros da amostra, foi possÃvel separarmos as contribuiÃÃes dos RBMs nos espectros Raman relacionados aos tubos internos dos TWCNTs e DWCNTs, embora possuam a mesma distribuiÃÃo de diÃmetro, a resposta das propriedades vibracionais à pressÃo sÃo diferentes. Adicionalmente, foi possÃvel observar perfis de intensidades semelhantes para os modos RBMs dos tubos mais internos dos TWCNTs usando diferentes energias de LASER, mas sob diferentes condiÃÃes de pressÃo. AtribuÃmos este resultado à mudanÃas nas energias de transiÃÃes eletrÃnicas causadas por pequenas deformaÃÃes estruturais nos nanotubos induzidas pela pressÃo. CÃlculos teÃricos baseados em ab initio foram realizados para dar suporte Ãs interpretaÃÃes dos resultados experimentais. Para as amostras de MoS_2 esfoliadas, estudamos o efeito do empilhamento nos modos vibracionais E^1_{2g} e A_{1g} em altas pressÃes. Novas componentes para esses modos foram observadas com o aumento da pressÃo. Foi tambÃm observado que o coeficiente de pressÃo do modo E^1_{2g} diminui exponencialmente com o aumento do nÃmero de camadas, diferentemente do modo A_{1g} e das novas componentes, que nÃo apresentam uma dependÃncia significativa com a variaÃÃo da espessura do MoS_2. AtribuÃmos estes resultados Ãs deformaÃÃes estruturais do MoS_2 induzidas por uma tensÃo biaxial (dependente da adesÃo entre SiO_2 e MoS_2) resultante da deformaÃÃo do substrato de SiO_2. O aumento do nÃmero de camadas diminui a adesÃo entre o MoS_2 e o SiO_2 devido ao aumento da porcentagem de regiÃes em nÃo-contato com o substrato, e como consequÃncia, uma pressÃo mais elevada à necessÃria para aumentar a adesÃo, resultando no aumento da pressÃo para deformar a estrutura do MoS_2. Para o pà microcristalino de MoS2, com exceÃÃo dos modos B_{1u}, E^2_{2g}, E1g, E^1_{2g} e A_{1g}, o comportamento de todos os outros modos foi tambÃm estudado em condiÃÃes de altas pressÃes hidrostÃticas. Todos os modos apresentaram uma variaÃÃo linear de suas frequÃncias Raman com a pressÃo e coeficientes de pressÃo positivos. AlÃm disso, as diferenÃas no comportamento dos perfis de intensidade dos modos A_{1g}, 2LA(M) e A_{2u} em ressonÃncia e fora de ressonÃncia foram interpretados como sendo devido Ãs variaÃÃes nas energias das transiÃÃes Ãpticas direta induzidas pela pressÃo. / In this work we present the studies on Double (DWCNTs) and Triple Wall Carbon Nanotubes, on molybdenum disulfide in the bulk form and on few layer of MoS_2 under hydrostatic high pressure conditions. Theoretical calculations were performed in collaboration to support the experimental results. For the DWCNTs samples, changes in the G-band frequency vs. pressure plot and the disappearance of the radial breathing modes (RBM) between 2 GPa and 5 GPa indicate the beginning and ending of the radial collapse of the nanotubes. Theoretical calculations based on Density-Functional Tight-Binding (DFTB) shown that the collapse pressure (P_c) for DWCNTs follows a d^{-3}_{in} law, in excellent agreement with the experimental results. The P_c dependence on number of tube-walls and on the inter-wall distance is also investigated. For the TWCNTs samples, pressure screening effects are observed for the innermost tubes of TWCNTs similar to what has been already found for DWCNTs. However, using the RBM pressure coefficients in conjunction with the histogram of the diameter distribution, we were able to separate the RBM Raman contribution related to the intermediate tubes of TWCNTs from that related to the inner tubes of DWCNTs. By combining Raman spectroscopy and high pressure measurements, it was possible to identify these two categories of inner tubes even if the two tubes exhibit the same diameters, since their pressure response is different. Furthermore, it was possible to observe similar RBM profiles of the innermost tubes of TWCNTs using different resonance laser energies but also under different pressure conditions. This is attributed to changes in the electronic transition energies caused by small pressure-induced deformations. Theoretical calculations based on ab initio were performed for support the experimental results. By using Raman spectroscopy, it was possible to estimate the displacement of the optical energy levels with pressure. For the exfoliated MoS_2 samples, we studied the effect of the stacking on the E^1_{2g} and A_{1g} vibrational modes at high pressures. New components for both modes were observed with increasing pressure. It was also observed that the pressure coefficient of the E^1_{2g} mode decreases exponentially with MoS_2 thickness is increased, differently of the A_{1g} mode and the new components, which do not present a significant dependence on the variation of the number of layers. These results were attributed to deformations in the MoS_2 structure induced by a biaxial strain (dependent on the number of layers), resulting from the deformation of the SiO_2 substrate. Such adhesion decreases with the increasing of the MoS_2 thickness due to the increasing on the unbinding regions between MoS_2 and SiO_2. As result, a higher pressure is needed to improve the adhesion and consequently, a higher pressure is required to achieve the biaxial strain. For the MoS_2 microcrystalline powder, except for the B_{1u}, E^2_{2g}, E_{1g}, E^1_{2g} and A_{1g} modes, the behavior of all other modes was studied for the first time in high pressure conditions. For all modes, a linear variation of the Raman frequency and positive pressure coefficient was observed. Moreover, the differences in the behavior of the intensity profiles of the A_{1g}, 2LA(M) and A_{2u} modes in resonance and off-resonance were attributed to variations in the energy of direct optical transitions induced by pressure.

Este trabalho foi dividido em quatro etapas, além da introdução. A primeira parte consiste no estudo comparativo do comportamento eletroquímico de eletrodos de cobre em soluções tampão fosfato 0,10 mol L-1 com valores de pH 4,5 e 7,8, e em solução de NaOH com valores de pH 13,0 e 14,0. Mostrou-se que as espécies formadas eletroquimicamente sobre a superfície do eletrodo são dependentes do valor de pH e do potencial aplicado. Os resultados experimentais obtidos estão de acordo com aqueles reportados na literatura. A segunda parte da tese corresponde ao desenvolvimento de um sensor eletroquímico fabricado com microeletrodos de cobre para a determinação de peróxido de hidrogênio (H2O2) em amostras comerciais de antissépticos bucais e clareadores dentais. Nas condições experimentais otimizadas (solução tampão fosfato 0,10 mol L-1 (pH 7,0) e potencial de redução de -0,20 V), microeletrodos de cobre foram utilizados para a determinação de H2O2 sem a necessidade de etapas de extração, obtendo-se faixa linear de 0,015 a 6,4 mmol L-1 e limite de detecção de 2,8 µmol L-1. O método proposto mostrou-se reprodutível e a presença de interferentes na matriz da amostra analisada não alterou a resposta do sensor para H2O2. Na terceira parte, a reação de eletro-oxidação de glicerol em superfícies de cobre em soluções de NaOH foi investigada utilizando a microscopia eletroquímica de varredura (SECM) no modo de geração pelo substrato de cobre / coleta no microeletrodo de platina (tip) (SG/TC). Os experimentos com a SECM mostraram a dependência da corrente com a distância entre o gerador e a tip, assim como a dependência com a concentração da solução de NaOH. Além disso, a corrente monitorada no microeletrodo diminuiu significativamente após a adição de glicerol. A atividade eletrocatalítica de eletrodos de cobre, no que diz respeito à oxidação de glicerol em meio alcalino, permitiu o desenvolvimento de um sensor amperométrico para a determinação de glicerol em amostra de biodiesel, com um intervalo linear de 0,05 a 1,33 mmol L-1 e limite de detecção de 20 µmol L-1. A metodologia proposta foi aplicada para a determinação do analito em uma amostra de biodiesel de mamona. A quarta parte descreve a síntese, caracterização eletroquímica e utilização de nanotubos de carbono de paredes múltiplas (NCPM) decorados com nanopartículas de paládio (Pd) para a modificação da superfície de eletrodo de carbono vítreo (CV) para a oxidação de metanol, etanol e glicerol em solução de KOH 1,0 mol L-1. Os resultados mostraram que o NCPM/Pd é um bom catalisador para a eletro-oxidação de álcoois em meio alcalino e que maior atividade eletrocatalítica foi obtida para o glicerol. Em condições otimizadas, experimentos amperométricos foram realizados para o desenvolvimento do método analítico para a determinação de glicerol em biodiesel, obtendo-se um intervalo linear de 0,06 a 24 mmol L-1 e limite de detecção 30 µmol L-1. Amostras de biodiesel foram analisadas com sucesso por meio de curvas de adição de padrão utilizando o eletrodo CV/NCPM/Pd. / This thesis is divided into four parts, apart from a general introduction. Part 1 is concerned with a critical comparison of the electrochemical behaviour of copper electrodes, in 0.10 mol L-1 phosphate buffer solution (pH 4.5 and 7.8), and in NaOH solution (pH 13.0 and 14.0). The electrochemical study showed that the species formed on the surface depends on both pH and the applied potential. The experimental results are in good agreement with those reported in the literature. A second goal of the thesis was the development of an electrochemical sensor for hydrogen peroxide (H2O2) determination in commercial oral antiseptic and dental whitening samples using copper microelectrodes. With optimized experimental conditions (working potential applied = -0.20 V in 0.10 mol L-1 phosphate buffer solution pH= 7.0), copper microelectrodes can be used to detect H2O2 without any previous extraction steps, in the range of 0.015 to 6.4 mmol L-1 with a lower detection limit of 2.8 µmol L-1. In addition, the electrode exhibited an excellent reproducibility and long-term stability as well as negligible interference from sorbitol, ethanol, glycerin and saccharin. In the third part, the electrooxidation reaction of glycerol at copper surfaces in NaOH solutions was investigated using Scanning Electrochemical Microscopy (SECM) in a copper substrate generation / platinum microelectrode (tip) collection mode (SG/TC). The results showed the dependence of the current measured at the tip with respect to the distance between generator and the tip, as well as on the concentration of the NaOH solution. Other studies led to the conclusion that the current measured at the tip decreased significantly after addition of glycerol in the solution. The electrocatalytic activity of copper electrodes for the oxidation of glycerol in alkaline medium allowed the development of an amperometric method to determine glycerol in biodiesel samples in the range 0.05 to 1.33 mmol L-1 with a detection limit of 20 µmol L-1. The determination of the analyte in a castor biodiesel sample employing a single copper microelectrode was carried out. The four part of this thesis shows results on the synthesis, electrochemical characterization and use of a glassy carbon (GC) electrode modified with multi-wall carbon nanotubes (MWCNT) decorated with palladium (Pd) for the electrochemical oxidation of methanol, ethanol and glycerol in 1.0 mol L-1 KOH solution. The results showed that MWCNT/Pd is a good electrocatalyst for methanol, ethanol and glycerol oxidation in alkaline medium, with highest activity toward glycerol oxidation. With optimized experimental conditions, an amperometric method was developed for the determination of glycerol in biodiesel samples, in the range of 0.06 to 24 mmol L-1 and detection limit of 30 µmol L-1. Biodiesel samples were successfully analyzed by the standard addition method using the GC/MWCNT/Pd film electrode.

Orientador: Marcos Akira D' Ávila / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-24T19:12:36Z (GMT). No. of bitstreams: 1 Almeida_RosemeiredosSantos_D.pdf: 3414008 bytes, checksum: 9f5516445d3c90d0f22d3a953197d6b7 (MD5) Previous issue date: 2014 / Resumo: O polímero Poli(caprolactona) (PCL) tem sido amplamente usado como biomaterial nas últimas décadas. Sua biocompatibilidade e boas propriedades termo-mecânicas são as principais características que levam à seleção desse material para aplicação nas áreas biotecnológica, farmacêutica e têxtil. Neste trabalho, montou-se um equipamento para realizar o processamento de eletrofiação e caracterização de mantas formadas por fibras de PCL puro e nanocompósitos de PCL/nanotubos de carbono (NTC). Recorreu-se à eletrofiação com a aplicação de um campo elétrico gerado por uma corrente alternada (CA) e por uma corrente contínua (CC) simultaneamente (CA/CC) visando o controle da estabilidade do escoamento do jato polimérico durante o processamento a fim de determinar os parâmetros de processo e comparar os efeitos das diferentes frequências durante o processamento. Foram obtidos também nanocompósitos de PCL/óxido de grafeno (GO) com aplicação de um potencial elétrico em corrente contínua (CC), a fim de determinar os parâmetros de processos em diferentes concentrações de óxido de grafeno. As soluções/suspensões utilizadas no processo foram caracterizadas através de medições de condutividade elétrica, tensão superficial e propriedades reológicas. As fibras obtidas na forma de mantas porosas não-tecidas (non woven) foram caracterizadas por Microscopia Eletrônica de Varredura (MEV), Espectroscopia de Infravermelho com Transformada de Fourier (FT-IR), Calorimetria Exploratória Diferencial (DSC), Análise Termogravimétrica (TGA), Resistividade, Ângulo de contato ensaios mecânicos de tração e ensaios biológicos in vitro com células tronco mesenquimais humanas (hMSCs). Observou-se que o diâmetro médio das fibras depende da frequência CA aplicada durante a eletrofiação. A análise por FT-IR mostrou que houve a interação entre o PCL e o NTC, e as análises biológicas indicaram que as mantas PCL/GO são promissoras para uso como biomaterial / Abstract: Poly (??caprolactone) (PCL) has been widely used as biomaterial in the last decades. Its biocompatibility and good thermomechanical properties are the main features that lead to the selection of this material for applications in biotechnological, pharmaceutical and textile areas. In this work, an equipment was set up to perform electrospinning; characterization of fibrous mats formed by pure PCL fibers and nanocomposites of PCL/carbon nanotubes (CNT). Electrospinning based on the application of an electric field generated by an alternating current (AC) and a direct current (DC) simultaneously (AC/DC) was performed aiming to control the stability of the jet flow of the polymer during processing in order to determine the process parameters and compare the effects of different frequencies during processing. Nanocomposites of PCL/graphene oxide (GO) with application of a DC electrical potential were also obtained in order to determine the process parameters at different concentrations of graphene oxide. Solutions/suspensions employed in the process were characterized by measurements of electrical conductivity, surface tension and rheological properties. The fibers obtained in the form of non- woven porous mats were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR), Differential canning Calorimetry (DSC), Thermogravimetric Analysis (TGA), resistivity, contact angle and mechanical properties was measured, and in vitro biological assays with human mesenchymal stem cells (hMSCs) was evaluated. It was observed that the average diameter of the fibers depends on the AC frequency applied during electrospinning. The FT-IR analysis showed that there was interaction between the PCL and the CNTs, and biological analysis indicated that the blankets of PCL/CNT and PCL/GO are promising for use as a biomaterial / Doutorado / Materiais e Processos de Fabricação / Doutora em Engenharia Mecânica

Orientadores: Ana Flávia Nogueira, Valtencir Zucolotto / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-22T02:59:18Z (GMT). No. of bitstreams: 1 Almeida_LuizCarlosPimentel_D.pdf: 6880507 bytes, checksum: f7a2c24853f25411226ae9b66a2de97b (MD5) Previous issue date: 2012 / Resumo: Neste trabalho foram estudados filmes finos multicamadas baseados em polímeros condutores, nanotubos de carbono e um derivado de fulereno. Esses filmes foram depositados pela técnica de deposição camada por camada (LbL) via interações eletrostáticas. Esse trabalho está dividido em duas partes: 1-) Filmes LbL baseados no polímero conjugado poli(p-fenilenovinileno) (PPV) e nanotubos de carbono de parede única funcionalizados com grupos carboxílicos (SWNTCOOH) foram preparados em arquitetura de bloco, caracterizados e aplicados como fotoeletrodos em células solares fotoeletroquímicas. A morfologia desses filmes foi avaliada por microscopia de força atômica (AFM) e de epifluorescência, as quais indicaram uma variação morfológica significativa dos filmes após adição de camadas de nanotubos de carbono. A transferência de carga fotoinduzida do polímero condutor PPV para o SWNT-COOH foi analisada por supressão de fotoluminescência (PL). A caracterização fotoeletroquímica foi realizada sob irradiação de luz branca e os fotoeletrodos contendo SWNT-COOH apresentaram valores de fotocorrente de até 7,5 mA cm. A fotocorrente aumentou e tornou-se mais estável quando uma camada do polímero poli(3,4-etilenodioxitiofeno) dopado com poli(4-sulfonato de estireno) (PEDOT:PSS) foi depositada entre o eletrodo ITO e o filme LbL. 2-) Foram preparados filmes LbL baseados no polímero conjugado poli[2-(3-tienil)-etoxi-4-butilsulfonato] de sódio (PTEBS) e no derivado de fulereno C60-F. A caracterizacao fotofísica mostrou a ocorrência de transferência fotoinduzida de carga do PTEBS para o C60-F, a qual foi também demonstrada por meio da geração de fotocorrente obtida quando os filmes (PTEBS/C60-F) foram aplicados como fotoeletrodos em células solares fotoeletroquímicas. Os resultados obtidos fazem dos filmes LbL baseados em semicondutores orgânicos candidatos promissores para conversão de energia solar. / Abstract: In this work, multilayer thin films based on conducting polymers, carbon nanotubes and fullerene derivatives were studied. These films were fabricated by layer-by-layer deposition technique (LbL) through electrostatic interactions. This work is divided in two parts: 1-) LbL films composed of a conducting polymer poly(p-phenylenevinylene) (PPV) and carboxylic acid functionalized singlewalled carbon nanotubes (SWNT-COOH) were prepared in a block architecture, characterized and applied as electrodes in photoelectrochemical solar cells. Film morphology was evaluated by atomic force and epifluorescence microscopies, showing remarkable changes after incorporation of SWNT-COOH layers. The photoinduced charge transfer from the conducting polymer to SWNT-COOH was analyzed by photoluminescence (PL) quenching. Photoelectrochemical characterization was performed under white light and the films containing SWNTCOOH displayed photocurrent values up to 7.5 mA cm. Photocurrent generation was enhanced and became more stable when an intermediate layer of poly(3,4- ethylenedioxythiophene)¿poly(4-styrenesulfonic acid) (PEDOT:PSS) was interposed between the ITO electrode and LbL films. 2-) LbL films based on the conducting polymer sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate] (PTEBS) and fullerene derivative C60-F were fabricated. Photophysical characterization shows the occurrence of photoinduced charge transfer from PTEBS to C60-F, which was also demonstrated by photocurrent generation obtained when (PTEBS/C60-F) multilayer films were applied as electrodes of photoelectrochemical solar cells. All these results make the LbL films based on organic semiconductors promising canditates towards solar energy conversion. / Doutorado / Físico-Química / Doutor em Ciências

An ideal biosensor is a compact and in-expensive device that is able to readily and rapidly detects different types of analytes with high sensitivity and specificity. The affectability of a biosensing methodology is subject to the limit of nanomaterials to transduce the target binding process to an improved perceptible signal, while the selectivity is accomplished by considering the binding and specificity of certain moieties to their targets. Keeping these requirements in mind we have chosen nanomaterials such as carbon nanotubes (CNTs) and gold nanoparticles (AuNPs) that has catalytic properties combined with their size, shape and configuration dependent chemical and physical properties as essential precursors and signaling components for creation of biosensors with tremendous sensitivity. The primary goal of the research work described in this dissertation is to develop and evaluate novel methods to detect various analytes using nanomaterials, at the same time making an affordable architecture for point-of-care (POC) applications. We report here in chapter 3 a simple and new strategy for preparing disposable, paper-based, porous AuNP/M-SWCNT hybrid thin gold films with high conductivity, rapid electron transfer rates, and excellent electrocatalytic properties to achieve multiple analyte electrochemical detection with a resolution that greatly exceeds that of purchased flat gold slides. We further explored the use of nanomaterial-based paper films in more complex matrices to detect analytes such as NADH, which can act as a biomarker for certain cellular redox imbalances and disease conditions. Carbon nanotubes with their large activated surfaces and edge-plane sites (defects) that are ideal for performing NADH oxidation at low potentials without any help of redox mediators minimizing surface fouling in complex matrices is described in chapter 4. With an instrument-free approach in mind we further focused on a colorimetric platform using split cocaine aptamers and gold nanoparticles (AuNPs) to detect cocaine for on-site applications as described in chapter 5. In chapter 5, the split aptamer sequences were evaluated mainly on three basic criteria, the hybridization efficiency, specificity towards the analyte (cocaine), and the reaction time to observe a distinguishable color change from red to blue. The assay is an enzyme-assisted target recycling (EATR) strategy following the principle that nuclease enzyme recognizes probe–target complexes, cleaving only the probe strand releasing the target for recycling. We have also studied the effect of the number of binding domains with variable chain lengths on either side of the apurinic (AP) site. On the basis of our results, we finally shortlisted the sequence combination with maximum signal enhancement fold which is instrumental in development of colorimetric platform with faster, and specific reaction to observe a distinctive color change in the presence of cocaine.

Abstract Carbon nanotubes are a promising material for various applications due to their unique collection of properties. However, carbon nanotube material as such is inert and insoluble, which hampers the true realization of its potential. In order to enhance the applicability of carbon nanotubes, their surface must be modified. This work concerned the chemical modification of single-walled carbon nanotubes (SWNT) by the Birch reduction, which is based on the reduction of the SWNT surface with the valence electron of alkali metal solvated in liquid ammonia. The reduction generates a SWNT anion, which reacts with electrophiles resulting in the covalent attachment of functional groups to the tube surface. In this work, aryl halides or alcohols were used as electrophiles to yield arylated or hydrogenated SWNTs, respectively. At first, the goal was to modify SWNTs as a filler material for polystyrene. The use of five halogenated ethenylphenyl derivatives as electrophiles revealed that the structure of electrophile affected the success of functionalization and the solubility of SWNTs in polystyrene-toluene solution. The most successful functionalization and solubilization of SWNTs were achieved with 1-chloro-4-ethenylbenzene. In the second part, liquid ammonia was replaced with a new solvent, 1-methoxy-2-(2-methoxyethoxy)ethane (diglyme) in order to avoid the restrictions, hazards and inconvenience of its handling. The work concentrated on the study of alkali metal reduction of SWNTs in diglyme by the use of arylation with 4-iodobenzoic acid or 4-chlorobenzoic acid and hydrogenation as model reactions. Li, Na or K was used as an alkali metal while naphthalene or 1-tert-butyl-4-(4-tert-butylphenyl)benzene was used in order to enhance the solvation of electrons. As a result, functionalization was simplified and enhanced. Electrophile affected the functionalization in such a way that arylation was significantly more successful than hydrogenation. The effect of alkali metal and electron carrier varied with electrophile. The most successful hydrogenation was achieved with the complex of Li and 1-tert-butyl-4-(4-tert-butylphenyl)benzene while arylation was the most successful with the complex of K and naphthalene. The solubility of SWNTs in water, ethanol, methanol and dimethylformamide was clearly improved by arylation whereas hydrogenation led to moderate improvement. / Tiivistelmä Hiilinanoputket ovat ainutlaatuisten ominaisuuksiensa vuoksi lupaava materiaali moniin sovelluksiin, mutta liukenemattomuus ja epäreaktiivisuus haittaavat niiden tehokasta hyödyntämistä. Käytettävyyttä voidaan parantaa kemiallisella modifioinnilla. Tässä työssä yksiseinäisiä hiilinanoputkia modifioitiin Birch-pelkistyksellä, joka perustuu putken pinnan pelkistykseen nestemäiseen ammoniakkiin solvatoituneella alkalimetallin valenssielektronilla. Pelkistyksessä hiilinanoputkesta muodostuu anioni, joka reagoi elektrofiilin kanssa johtaen funktionaalisten ryhmien kovalenttiseen sitoutumiseen putken pintaan. Tässä työssä hiilinanoputkia aryloitiin käyttämällä aryylihalideja elektrofiilinä tai vedytettiin käyttämällä alkoholia. Aluksi tavoitteena oli hiilinanoputkien modifiointi sellaiseen muotoon, että niitä voitaisiin käyttää polystyreenin täyteaineena. Viittä aryylihalidia käyttämällä havaittiin, että elektrofiilin rakenne vaikutti funktionalisoinnin määrään ja putkien liukoisuuteen polystyreeni-tolueeni-liuokseen. 1-Kloori-4-etenyylibentseenillä saavutettiin onnistunein arylointi ja paras liukoisuus. Työn toisessa osassa luovuttiin ammoniakin käytöstä siihen liittyvien rajoitteiden ja haittojen vuoksi. Keskityttiin hiilinanoputkien alkalimetallipelkistyksen tutkimiseen uudessa liuottimessa, 1-metoksi-2-(2-metoksietoksi)etaanissa (diglyymi). Mallireaktioina käytettiin arylointia 4-jodibentsoehapolla tai 4-klooribentsoehapolla ja vedytystä alkoholilla. Ammoniakin korvaaminen diglyymillä yksinkertaisti ja tehosti funktionalisointia. Reaktiot suoritettiin eri alkalimetalleilla (Li, Na tai K). Naftaleenia tai 1-tert-butyyli-4-(4-tert-butyylifenyyli)bentseeniä käytettiin elektronien solvatoinnin parantamiseksi. Elektrofiilin rakenne vaikutti funktionalisointiin siten, että aryylihalidi johti huomattavasti onnistuneempaan funktionalisointiin kuin alkoholi. Alkalimetallin ja elektroninkantajamolekyylin vaikutus vaihteli elektrofiilin mukaan. Litiumin käyttö 1-tert-butyyli-4-(4-tert-butyylifenyyli)bentseenin kanssa johti onnistuneimpaan vedytykseen. Kaliumin käyttö naftaleenin kanssa johti onnistuneimpaan arylointiin. Hiilinanoputkien liukoisuus vaihteli elektrofiilin mukaan. Arylointi paransi selkeästi hiilinanoputkien liukoisuutta veteen, etanoliin, metanoliin ja dimetyyliformamidiin. Vedytyksen vaikutus liukoisuuteen oli vähäisempi.

Carbon nanotubes (CNTs) and gold nanoparticles (AuNPs) are widely used for sensing applications due to their distinctive electrical and optical properties, and we have explored the development of methods that enable the incorporation of these nanomaterials into new and improved sensing devices. As a means for fabricating simple, low-cost and fast detection platforms for various applications, we have developed paper-based electrochemical detection platforms based on CNTs or platinum nanoparticle (PtNP)-CNT composite materials. We describe the use of a paper-based, low density, a three-dimensional thin film of interconnected CNTs as an electrode material. We studied the electrochemical properties of these paper-based CNT electrodes and demonstrated their use as an electrochemical sensor for the sensitive detection of guanine-based nucleotides. We further describe the functionalization of this paper-based electrode by fabricating a PtNP-SWCNT hybrid film via a vacuum filtration-based method. The interconnected PtNP structure formed on top of the CNT-coated paper was directly used as an electrocatalyst for methanol oxidation. Compared to paper-based PtNP-SWCNT hybrid films formed by electrochemical deposition, hybrid films formed by vacuum filtration showed a higher electrochemical surface area and enhanced electrocatalytic response to methanol oxidation. We have also developed methods based around DNA-modified AuNPs, which offer an excellent colorimetric platform for target detection. The DNA density on the surface of modified AuNPs affects enzymatic activity, colloidal stability of AuNPs, the orientation of the probe DNA and its hybridization efficiency. The combination of all these factors ultimately dictates the reaction time and sensitivity of colorimetric assays. We demonstrate the use of DTT as a modulator to control DNA surface coverage on the surface of AuNPs. Using this DTT treatment and a novel probe for exonuclease III activity, we have developed a colorimetric assay based on DTT-treated, DNA-modified AuNPs that can achieve more sensitive and rapid detection of DNA and enzymes relative to existing sensor platforms.

This thesis is divided into two parts; the first part presents results on the effect of the flow of fluids and electrochemical bias on single walled carbon nanotubes (SWNT). Issues pertaining to the entry of water into the cylindrical pores of the SWNT and its freezing dynamics have also been addressed in the first part of the thesis. The second part of the thesis deals with Raman scattering studies of iron perovskite namely CaFeO3 and La0.33Sr0.67FeO3 across their charge-disproportionation transition temperatures. PART 1 Chapter 1: Introduction This chapter presents an overview of the systems studied in this thesis, i.e., (i) SWNT and (ii) iron perovskite’s containing iron in Fe4+(d4) state, namely CaFeO3 and La0.33Sr0.67FeO3. It also contains an introduction to the two spectroscopic techniques used in the present thesis, namely Raman scattering and Nuclear Magnetic Resonance. A quantum mechanical picture of Raman scattering, in general, and resonance Raman scattering in particular along with a brief introduction to the apparatus used both for the micro Raman and the low temperature experiments is presented in this chapter. A general introduction to Nuclear Magnetic Resonance (NMR) is also given with an emphasis on various interactions leading to the broadening of the NMR absorption linewidths. Chapter 2: Carbon nanotube liquid flow sensors This chapter presents experimental results and theoretical understandings of the generation of electrical signals by flowing polar/ionic liquids over a mat of SWNT. We first present experimental findings that the flow of a variety of liquids on SWNT bundles induces an electrical signal (voltage/current) in the sample along the direction of the flow. The electrical response is found to be a logarithmic function of the flow speed over a wide range. The magnitude of the signal generated depends sensitively on the ionic conductivity and the polar nature of the liquid and weakly on the viscosity of the liquid. Furthermore its direction can be controlled by electrochemical biasing of the nanotubes. The ratio of the open circuit voltage to the short circuit current is found to be governed by the nanotube resistance. These experimental findings are inconsistent with the conventional idea of a streaming potential as the possible cause. Our measurements suggest that the dominant mechanism responsible for this highly sub-linear response should involve a direct forcing of the free charge carriers in the nanotubes by the fluctuating Coulombic field of the liquid flowing past it. Two alternative understandings of the experimental findings are also presented in this chapter. The first mechanism invokes the idea of a “pulsating ratchet” whereby the charge carriers in the nanotubes experience an asymmetric spatial bias because of the shear-induced deformation of the ion-plus-polar atmosphere at the liquid-solid interface temporally modulated by the liquid flow. In addition, we also propose that experimental findings can be understood qualitatively in terms of three interrelated ideas: (a) Induced friction: The fluctuating charge density of the ions close to the nanotube couples coulombically to the charge carriers in the nanotube and, therefore, offers a friction to the motion of these charge carriers (in addition to the Ohmic friction intrinsic to the carbon nanotubes); (b) Flow-induced drag: In virtue of the above frictional coupling, an imposed liquid flow drags the charge carriers along through the nanotube; (c) Reduction of induced friction at high flow speeds: The space-time correlated Coulombic fluctuations, inherent to the liquid electrolyte, are advected by the liquid flow, and thus get Galilean boosted (Doppler shifted) as seen in the mean rest frame of the drifting carriers in the nanotube. This would cause a reduction of the frictional grip to the motion of the charge carriers in the nanotube with increasing flow speed resulting in a sublinear dependence of the charge drift-velocity (electrical response) on the liquid flow speed. With the above in mind, a quantitative derivation of these frictional effects, first from a heuristic argument, and then analytically from a Langevin-equation treatment have been presented. Chapter 3: Direct generation of voltage and current by gas flow over carbon nanotubes and semiconductors Having obtained experimental evidence of the generation of liquid flow induced electrical signals over single-walled carbon nanotubes, it was only natural to look for the same effect by flowing gases over nanotubes. We show here a direct generation of measurable voltages and currents when gas flows at modest speeds of a few meters per second over single-walled carbon nanotubes . Interestingly, unlike the previous effect (generation of voltages by flow of liquids over single-walled carbon nanotubes), this effect is not specific to single-walled carbon nanotubes and occurs for a wide variety of solids, including single and multi-walled carbon nanotubes, doped semiconductors and metals. Moreover, the gas flow induced signals depend quadratically on the gas flow velocities. This is in sharp contrast to the results obtained by flowing liquids over single-walled carbon nanotubes where the liquid flow generated signal was found to be logarithmically dependent on the flow velocities. In this chapter we provide evidence that the underlying mechanism for the gas flow generated electrical signal is an interplay of Bernoulli’s principle and the Seebeck effect: Pressure difference along streamlines gives rise to temperature difference across the sample which, in turn, produces the measured voltage. Chapter 4: Water at nanoscale confined in single-walled carbon nanotubes studied by NMR In this chapter, we seek experimental evidence of the occupancy of water in the cylindrical pores of the nanotubes. Proton NMR studies have been carried out as a function of temperature from 210 K to 300 K of water confined within SWNT. The NMR lineshape at and below the freezing point of bulk water is asymmetric which can be decomposed into a sum of two Lorentzians. The intensities of both the components decrease with lowering of temperature below 273 K, one component L1 vanishing below 242 K and the other component L2 below 217 K. Following the simulations of Koga et al. (Nature, 412, 802, 2001) showing that the radial density profile of confined water in SWNT has a distribution peak at the center which disappears below the freezing temperature, the L1 component is associated with the protons of the water molecules at the center and the L2 component is associated with protons of water molecules associated at a distance ~ 3Å away from the walls of the nanotubes. In this scenario the complete freezing of the water at ~ 212 K is preceded by the withdrawal of the water molecules from the center of the nanotubes. Chapter 5: Electrochemical tuning of band structure of single walled carbon nanotubes probed by in-situ resonance Raman scattering The work presented in this chapter is motivated by the experimental observation that SWNT have excellent actuating properties, i.e, porous sheets of carbon nanotubes were shown to suffer length changes when subjected to electrochemical bias, with action observed up to 1 KHz. The fast response of the nanotube actuator rules out any mechanism related to the intercalation of ions as is applicable to the case of the polymer actuators. This chapter presents results of in-situ resonance Raman scattering of SWNT investigated under electrochemical biasing. The experimental results show that the intensity of the radial breathing mode varies significantly in a non-monotonic manner as a function of the cathodic bias voltage, but does not change appreciably under anodic bias. The tangential mode is, however, not affected. These results can be quantitatively understood in terms of the changes in the energy gaps between the one-dimensional van Hove singularities in the electron density of states arising possibly due to the alterations in the overlap integral of π-bonds between the p-orbitals of adjacent carbon atoms. This chapter also contains results from ab-initio restricted Hartree Fock calculations in a simplistic geometry where a nanotube is surrounded by two concentric rings of ions. The ab-initio calculation results suggest that the dominant contribution to the strain developed in the nanotubes originates from the electrostatic interactions between the ions and the delocalized π electrons as compared to the doping effects. PART 2 Chapter 6: Raman scattering in CaFeO3 and La0.33Sr0.67FeO3 across the charge disproportionation phase transition Temperature dependent micro-Raman studies of orthorhombic CaFeO3 and rhombohedral La0.33Sr0.67FeO3 were carried out with an aim to study the role of phonons in the formation of the charge disproportioned state (Fe4+ → Fe5++Fe3+) below the transition temperature (Tco) of 290 K and 200 K, respectively. Shell model lattice dynamics calculations were performed for CaFeO3 to assign the Raman modes and determine their vibrational pattern. Temperature dependence of the peak positions and peak widths of various modes for both the systems show distinct changes across their respective transition temperatures. In CaFeO3 the symmetric stretching mode at 707 cm−1 splits into two modes, 707 cm−1 and 684 cm−1 . Interestingly, the 707 (684) cm−1 mode appears only in HH(HV) polarization. In comparison, the Raman band at 704 cm−1 in La0.33Sr0.67FeO3 which has been assigned to the Raman forbidden symmetric stretching mode, disappears below Tco. In addition, two modes at 307 cm−1 and 380 cm−1 of La0.33Sr0.67FeO3 approach each other at Tco. Our experiments show that for both the systems, CaFeO3 and La0.33Sr0.67FeO3, the lattice distortion changes across Tco. Chapter 7: Summary and future outlook The last chapter summarizes our main findings reported in the thesis. It also contains possible future studies which are worth pursuing to add further insights in the issues addressed.

abstract: Electrostatic Discharge (ESD) is a unique issue in the electronics industry that can cause failures of electrical components and complete electronic systems. There is an entire industry that is focused on developing ESD compliant tooling using traditional manufacturing methods. This research work evaluates the feasibility to fabricate a PEEK-Carbon Nanotube composite filament for Fused Filament Fabrication (FFF) Additive Manufacturing that is ESD compliant. In addition, it demonstrates that the FFF process can be used to print tools with the required accuracy, ESD compliance and mechanical properties necessary for the electronics industry at a low rate production level. Current Additive Manufacturing technology can print high temperature polymers, such as PEEK, with the required mechanical properties but they are not ESD compliant and require post processing to create a product that is. There has been some research conducted using mixed multi-wall and single wall carbon nanotubes in a PEEK polymers, which improves mechanical properties while reducing bulk resistance to the levels required to be ESD compliant. This previous research has been used to develop a PEEK-CNT polymer matrix for the Fused Filament Fabrication additive manufacturing process / Dissertation/Thesis / Masters Thesis Engineering 2020