Philosophiae Doctor - PhD / The thesis presents a simple, sensitive, low cost and a novel graphenated polyaniline doped tungsten trioxide nanocomposite, as an electrochemical sensor for the detection and quantitative and determination of PAHs, which are ubiquitous, toxic, as well as dangerous organic pollutant compounds in the environment. The selected PAHs (anthracene, phenanthrene and pyrene) in wastewater were given priority as a result of their threat to human nature and that of the environment. In order for a healthy, non-polluted and well sustainable environment, there is need for an instrument that is capable of detecting and quantifying these organic pollutants onsite and also for constant monitoring. The nanocomposites were developed by chemical and electrochemical methods of preparations, exploiting the intrinsic properties of polyaniline, graphene and tungsten trioxide semiconducting materials. Chemically, graphene-polyaniline (GR-PANI) nanocomposite was synthesised by in situ polymerisation method, then casted on a surface of glassy carbon electrode to form GR-PANI modified electrode. The properties of the prepared electrode were investigated through morphological and spectroscopic techniques, which confirmed the formation of the composite. The electroactivity of the prepared modified electrode revealed great improvement in cyclic and square wave voltammetric response on anthracene. A dynamic range of 2.0 × 10-5 to 1.0 × 10-3 M and detection limit of 4.39 x 10-7 M was established.

>Magister Scientiae - MSc / Current water treatment technologies do not remove many endocrine disruptor compounds (EDCs) such as 17α-ethynylestradiol (EE2) in its entirety, and the amount of these pollutants that continues to enter the aquatic environment through wastewater effluents is still capable of causing harmful health effects. Therefore the development of simpler and more sensitive biosensor system for detection of EE2 must be developed which have high responsiveness, low cost and easy handling. Therefore the aim of this study was to work towards the development of rapid test system of polyaniline-laccase on gold enzyme nanobiosensor (PANI-PSSA/Lac/Glu) for water estrogens. Preliminary studies were first done on the materials used in this study: estrogens, laccase, gold nanoparticles (AuNPs), and electropolymerized PANI-PSSA. Laccase was shown to be active towards EE2 and the enzyme could be stored for over three months. EE2 solution also could be used for over three months. Buffer used in this study was found to be suitable. Phosphoric acid (H3PO4) was a suitable electrolyte than hydrochloric acid (HCl) to be used for the electropolymerization of aniline and was used because it has same ions as the McIlvaine buffer (McIlB) which the post-deposition CVs indicated the formation of electrochemically very stable film. AuNPs were successfully synthesized and its size was identified to be less than 22 nm. McIlB used for testing electrochemical properties of AuNP. CVs of GC/PANI-PSSA and GC/PANIPSSA/ Au showed no difference before and after exposure to aq. EE2 solution, an indication of being re-usable and could also serve as stable immobilising platform in laccase biosensor. When interrogating with electrochemical impedance spectroscopy (EIS), the charge transfer resistance (Rct) of both GC/PANI-PSSA and GC/PANI-PSSA/Lac/Glu showed an average increase by about 2.4% and 21% before and after exposure of EE2, respectively. This shows that the GC/PANI-PSSA/Lac/Glu was a functional EE2 biosensor and showing a positive step towards achieving a re-usable biosensor for EE2 as a model water estrogen. Future work Page | vi will focus on exploring different ways of improving the biosensor’s surface regeneration and its sensitivity to EE2.

Philosophiae Doctor - PhD / To meet a fast-growing market demand for next generation portable electronic devices with higher performance and increased device functionalities, efficient electrical energy devices with substantially higher energy, power densities and faster recharge times such as supercapacitors are needed. The overall aim of this thesis was to synthesize nanostructured sulphonated polyaniline and transition metal single, binary and ternary mixed oxide doped nanocomposites with electro-conductive properties. These nanocomposites were anchored on activated graphitic carbon and used in design of asymmetric supercapacitors. Tantalum(IV)oxide, tantalum(IV)oxide-nickel(II)oxide, tantalum(II)oxide-manganese(III)oxide, tantalum(II)oxide-nickel(II)oxide-manganese(II,III)oxide nanoparticles were synthesised using modified sol-gel methods. These were then dispersed, individually, in acidic media through sonication and incorporated in-situ into the polymeric matrix during the oxidative chemical polymerization of aniline doped with poly(4-styrene sulphonic acid). These novel polymeric nanocomposites were characterised with FTIR, UV-visible, TEM, SEM, EDS, XRD to ascertain successful polymerization, doping, morphology and entrapment of the metal oxide nanoparticles. SECM approach curves and interrogation of CV revealed that these nanocomposites are conductive and electro-active. The cells showed good supercapacitor characteristics with high specific capacitances of 170.5 Fg⁻¹ in TaO₂- PANi-PSSA, 166.1 Fg⁻¹ in TaO₂-NiO-PANi-PSSA, 248.4 Fg-1 in TaO-Mn₂O₃-PANi- PSSA and 119.6 Fg⁻¹ in TaO-NiO-Mn₃O₄-PANi-PSSA. Their corresponding energy densities were calculated as 245.5 Whg⁻¹, 179.4 Whg⁻¹, 357.7 Whg⁻¹ and 172.3 Whg⁻¹ respectively. They also gave respective power densities of 0.50 Whg⁻¹, 0.61 Whg⁻¹, 0.57 Whg⁻¹ and 0.65 Whg⁻¹ and showed good coulombic efficiencies ranging between 77.97% and 83.19%. These materials are found to have a long cycle life and therefore good electrode materials for constructing supercapacitor cells. / National Research Foundation (NRF)

Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-01-20Bitstream added on 2014-06-13T18:53:39Z : No. of bitstreams: 1 soares_la_me_ilha.pdf: 1532013 bytes, checksum: 0f4004d265a97a7015b084d2b64eb7b7 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho apresenta a preparação de um silsesquioxano nanoestruturado, o cloropropilsilsesquioxano (S) que foi organofuncionalizado com os seguintes agentes modificadores: 4-amino-3-hidrazinico-5-mercapto-1,2,4-triazol (Purpald®) e o 4-amino-5-4(piridil)-4H-1,2,4-triazol-3-tiol (APTT), os materiais obtidos dessa funcionalização foram descritos como SP e SA, respectivamente. Os materiais SP e SA foram caracterizados por diversas técnicas espectroscópicas: Espectroscopia na região do infravermelho (FT-IR), Ressonância magnética nuclear 29Si e 13C no estado sólido (RMN), Difração de Raios- X (DRX), Espectroscopia de Energia Dispersiva de Raios X (EDX), Termogravimetria e Análise Térmica Diferencial (TG – DTA). Após a devida caracterização, realizaram-se estudos de adsorção de íons metálicos (Cu2+, Cd2+ e Ni2+) nos sítios ativos do SA, porém, curiosamente não se observou a mesma capacidade de sorção pelo SP. Diferentes meios foram estudados no processo de adsorção dos íons metálicos supracitados: aquoso, etanólico 99% e etanólico 42%, determinando-se o tempo de equilíbrio de adsorção, que para ambos os meios e metais esse tempo máximo foi em média 35 min. Determinado o tempo de equilíbrio de adsorção dos íons metálicos em cada sistema, determinou-se a capacidade específica de sorção (Nfmax) através de isotermas de adsorção. Para o Cu2+, os valores de Nf foram: meio aquoso (3,09 × 10-4 mol g-1), etanólico 42% (1,03 × 10-4 mol g-1) e etanólico 99% (1,86 × 10-4 mol g-1), com concentrações de íons Cu2+ variando de 1,74 a 29,64 mol L-1. Os valores encontrados para o Ni2+ foram: em meio aquoso (2,11 × 10-4 mol g-1), etanólico 42% (0,97 × 10-4 mol g-1) e etanólico 99% (1,05 × 10-4 mol g-1), com concentrações de íons Ni2+ variando de 2,25 a 33,18 mol L-1. Para os íons cádmio não foram... / This work presents the preparation of a nanostructured silsesquioxane, the cloropropilsilsesquioxano (S) that was organofunctionalised with the following modifying agents: 4-amino-3-hydrazino 5 - mercapto 1,2,4 triazole (Purpald ®) and 4- amino-5-4 (pyridyl)-4H-1,2,4-triazole-3-thiol (APTT), the materials obtained of the functionalization were described as SP and SA, respectively. The materials SA and SP were characterized by various spectroscopic techniques such as spectroscopy in the region of infrared (FTIR), nuclear magnetic resonance 29Si and 13C solid-state (NMR), X-ray diffraction (XRD), Energy Dispersive Spectroscopy Rays (EDS), Thermogravimetry and Differential Thermal Analysis (TG - DTA). After proper characterization, were carried studies on adsorption of metallic ions such as Cu2+, Ni2+ and Cd2+ in the active sites of SA, but curiously did not observe the same sorption capacity of the SP. Different methods were studied in the adsorption of metal ions above: aqueous, 99% ethanolic and 42% ethanolic, determining the adsorption equilibrium time, which for both means and metals the maximum time averaged 35 min. After determining the adsorption equilibrium time of metal ions in each system, we determined the specific sorption capacity (Nfmax) through adsorption isotherms. For Cu2+, the values of Nf were: aqueous solution (3.09 × 10-4 mol g-1), 42% ethanolic (1.03 × 10-4 mol g-1) and 99% ethanolic (1.86 × 10-4 mol g-1), with Cu2 + ion concentrations ranging from 1.74 to 29.64 mol L-1. The values obtained for the Ni2+ were: aqueous solution (2.11 × 10-4 mol g-1), 42% ethanolic (0.97 × 10-4 mol g-1) and 99% ethanolic (1.05 × 10-4 mol g-1), with Ni2 + ion concentrations ranging from 2.25 to 33.18 mol L-1. For the cadmium ions were not observed saturation of adsorption sites in the concentration range studied, not getting the maximum... (Summary complete electronic access click below)

Submitted by TAMIRES ROCHA SOUZA (tami.rs.farm@gmail.com) on 2018-05-02T19:18:53Z No. of bitstreams: 1 DEFESA - VERSÃO FINAL.pdf: 3139508 bytes, checksum: fd4ffb1d470a0125ed405e09475c39eb (MD5) / Approved for entry into archive by Cristina Alexandra de Godoy null (cristina@adm.feis.unesp.br) on 2018-05-02T20:06:54Z (GMT) No. of bitstreams: 1 souza_tr_me_ilha.pdf: 3139508 bytes, checksum: fd4ffb1d470a0125ed405e09475c39eb (MD5) / Made available in DSpace on 2018-05-02T20:06:54Z (GMT). No. of bitstreams: 1 souza_tr_me_ilha.pdf: 3139508 bytes, checksum: fd4ffb1d470a0125ed405e09475c39eb (MD5) Previous issue date: 2018-03-09 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho descreve a preparação de partículas formadas a partir de Pentacianonitrosilferrato (III) de sódio e Cloreto de cádmio. As partículas foram preparadas em quatro proporções empregando os solventes Água/Formamida (100:0; 80:20; 40:60; 0:100) com o objetivo de investigar a sua influência na morfologia, topologia e nas propriedades eletrocatalíticas das partículas. Os materiais foram caracterizados por técnicas espectroscópicas e eletroquímica tais como: Espectroscopia na região do infravermelho (FTIR), Espectroscopia Raman, Reflectância difusa (UV-visível), Difração de raios-X (DRX), Microscopia eletrônica de varredura (MEV), Espectrometria de energia dispersiva de raios-X (EDS), Microscopia eletrônica de transmissão (MET) e voltametria cíclica (VC). Após as caracterizações foram realizados estudos sobre as propriedades eletroquímicas dos materiais utilizando um eletrodo de pasta de grafite. Dos quatro sistemas estudados, apenas dois foram sensíveis à concentrações de isoniazida, a saber o CdNP-3 e CdNP-4. Ambos os sistemas apresentaram duas regiões lineares de sinal em função da concentração com limites de detecção de 6,80×10-5 mol L-1 e 7,07×10-4 mol L-1, e 2,18×10-4 mol L-1 e 1,16×10-3 mol L-1 para os sistemas CdNP-3 e CdNP-4, respectivamente. Para o sistema CdNP-3 observou-se uma sensibilidade amperométrica de 23,96 mA mol L-1 e 10, 83 mA mol L-1, já para CdNP-4 observou-se uma sensibilidade amperométrica de 17,80 mA mol L-1 e 5,79 mA mol L-1 para cada região linear. / The present work describes the preparation of particles formed from Sodium Pentacyanonitrosylferrate (III) and Cadmium Chloride. The particles were prepared in four ratios using solvents Water / Formamide (100:0, 80:20, 40:60, 0:100) to investigate the influence on particle morphology, topology and electrocatalytic properties. The materials were characterized by spectroscopic and electrochemical techniques such as: Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Diffuse reflectance (UV-Visible), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), Transmission electron microscopy (TEM) and Cyclic voltammetry (CV). After the characterization studies, the electrochemical properties of materials were performed using a graphite paste electrode. Of the four systems studied, only two tests with concentrations of isoniazid, CdNP-3 and CdNP-4. Both systems presented two linear concentrations with detection limits of 6.80 × 10-5 mol L-1 and 7.07 × 10-4 mol L-1 and 2.18 × 10-4 mol L-1 and 1.16 × 10-3 mol L-1 for the CdNP-3 and CdNP-4 systems, respectively. For the CdNP-3 system, an amperometric sensitivity of 23.96 mA mol L-1 and 10.83 mA mol L-1 was observed, whereas for CdNP-4 an amperometric sensitivity of 17.80 mA mol L-1 and 5.79 mA mol L-1 for each linear region.

Philosophiae Doctor - PhD / In this work we primarily set out to investigate the technique of Aqueous Chemical Growth as a means of producing WO3 thin films that find applications in gas sensing and electrochromism. For the first time we demonstrated in this work, the heterogenous nucleation and growth of WO3 thin films on plain glass substrates and F-doped SnO2-glass substrates. This was achieved without the use of surfactants and template directing methods, using as a precursor solution Peroxotungstic Acid generated from the action of 30% H2O2 on pure W powder. The substrates used needed no surface-modification. On the plain glass substrates (soda lime silicates) a variety of micronanostructures could be observed prime of which were nanoplatelets that acted as a basic building block for the self-assembly of more hierarchical 3-d microspheres and thin films. On FTO a wide variety of micro-/nanostructures were observed dominant amongst which were urchin-like microspheres. The dominant crystallographic structure observed (through X-ray diffraction analysis, SAED, HRTEM) for the WO3 thin films on both substrate types post-annealing at 500 ˚C for a period of 1 - 2 h, was hexagonal-WO3. Next was monoclinic WO3. On rarer occasions the formation of triclinic and cubic WO3 was observed. The thin films produced showed a fairly high degree of porosity and had thicknesses in the range of 900 nm - 3.5 μm. I-V characterisation measurements using a 4-point collinear probe Keithley source alongside photoluminescence was used to establish the insulating nature of some of the films as well as their sub-stoichiometric nature. X-ray Photoelectron Spectroscopy was used to confirm the substoichiometric nature of some of the films.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-10-17T13:06:24Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Giselle BANCA.pdf: 2438394 bytes, checksum: 8b3d0cc9d7991a7ac011cdf4cdccabaf (MD5) / Made available in DSpace on 2016-10-17T13:06:24Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação Giselle BANCA.pdf: 2438394 bytes, checksum: 8b3d0cc9d7991a7ac011cdf4cdccabaf (MD5) Previous issue date: 2016-02-29 / FACEPE / A esquistossomose é um sério problema de saúde pública, é uma doença negligenciada e intimamente relacionada com baixos índices de desenvolvimento social. Neste trabalho, foi realizada uma detecção eletroquímica de DNA Schistosoma mansoni com base em uma monocamada auto-montada de ácido mercaptobenzóico (MBA) imobilizando nanoestruturas compostas por nanopartículas de ouro (AuNPs) e nanopartículas de magnetita (Fe3O4_NPs). Espectroscopia de impedância eletroquímica (EIS) e voltametria cíclica (CV) foram utilizadas para monitorar o evento de bioreconhecimento do sistema de MBA-Fe3O4_NPs-AuNPs-DNAsonda revela uma resposta eletroquímica eficaz indicando a modificação da superfície. O biosistema proposto foi capaz de reconhecer sequências de nucleótidos específica de S. mansoni presente em amostras de soro e líquido cefalorraquidiano (LCR) em diferentes concentrações de DNA do genoma. O resultado do bioreconhecimento gerou um aumento na resistência de transferência de elétrons e uma diminuição dos picos de corrente em concentrações de DNA durante as medições eletroquímicas. A plataforma desenvolvida mostrou um limite de detecção do DNA de 0,781 e 0,685 pg.μL- 1 para soro e LCR respectivamente. Portanto, o biossensor obtido pode ser considerado como um instrumento útil para a detecção especifica de S. mansoni em baixas concentrações em vários fluidos biológicos. / Schistosomiasis is a neglected disease closely related to the low levels of social development and a serious public health problem. In this work, we performed an electrochemical detection of Schistosoma mansoni DNA with a self-assembled monolayer of mercaptobenzoic acid (MBA) immobilizing nanostructures composed by gold nanoparticles (AuNPs) and magnetite nanoparticles (Fe3O4_NPs). Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) were used to monitor the biorecognition event. MBA-Fe3O4_NPs-AuNPs-DNAprobe system reveals an effective electrochemical response indicating the surface modification. The proposed biosystem was capable to recognize specific nucleotide sequence of S. mansoni present in cerebrospinal fluid (CFS) serum samples at different genome DNA concentrations. The biorecognition results in an increase in the electron transfer resistance and a decrease of the current peaks at higher DNA concentrations during electrochemical measurements. The developed platform showed a DNA detection limit of 0.781 and 0.685 pg.μL- 1 for serum and CFS, respectively. Therefore, the obtained biosensor can be considered as a useful tool for specific detection of S. mansoni at low concentrations in various biological fluids.

Molecular electrochemistry has proved to be very useful for characterizing redox reactions and deciphering chemical reaction mechanisms that are associated with electron transfer. It correlates strongly with redox-based medicine. In this study, we investigated the electrochemical behavior of pterocarpanquinones and selenoquinones, in protic and aprotic media, in the absence and presence of oxygen, in order to obtain data regarding their reduction mechanisms, reactivity with oxygen, the analysis of the stability of the electrogenerated intermediates and interactions with biological targets, like DNA. In typical measurements, CVs were recorded in aprotic medium (DMF + TBAPF6) to resemble the cell membrane environment. On the other hand, protic medium mimics the hydrophilic regions of the biological matrixes. This work shows cases of successful pharmacoelectrochemical investigations. In the first case, we investigate the electrochemical behavior of LQB-118, a pterocarpanquinone, which is anticancer and parasiticidal, with biological mechanisms of action related to the formation of ROS and interaction with DNA, among others. The cyclic voltammogram (VC) for LQB-118 in aprotic medium exhibits, at least, four waves. The first two are related to the usual reduction of quinones. The presence of additional waves suggests the clivage of the heterocyclic rings and the generation of additional reducible systems. A spectroelectrochemical investigation revealed the appearance of new absorption bands, which suggest the formation of the transient quinonamethide (QM). The QM was captured with thiophenol. In addition, electrochemical experiments were performed in the presence and absence of oxygen to verify the reactivity with oxygen, after the reduction of LQB-118 and its derivatives, with positive results. Studies with the ssDNA biosensor in solution showed positive interaction with LQB-118 and its electrogenerated products. The interaction of LQB-118 with CT-DNA was also evidenced by the fluorescence quenching technique. In the second case, CV was used to investigate the electrochemical behaviour of the antitumor selenoquinones. The obtained profiles confirmed the presence of two individual redox centres. All the compounds had shown electrochemical activity in the cathodic and anodic portions of the CVs. We also studied the behaviour of the compounds in protic medium. Electrochemical methods do well to predict the mechanism for adduct formation, structural rearrangement, generation of reactive oxigen species of pterocarpanquinones and appear well-adapted to explore redox pathways of all the compounds in vitro to be correlated to in vivo studies. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A eletroquímica molecular tem se mostrado muito útil para caracterizar reações redox e decifrar mecanismos reacionais associados à transferência de elétrons. Relaciona-se fortemente com a medicina redox. Neste estudo, investigou-se o comportamento eletroquímico de quinonas híbridas, tais como pterocarpanoquinonas e selenoquinonas, em meios prótico e aprótico, na ausência e presença de oxigênio, a fim de obter dados sobre seus mecanismos de redução e oxidação, reatividade com oxigênio, análise da estabilidade dos intermediários eletrogerados e interações com alvos biológicos importantes, como os tióis e o DNA. Em medidas típicas, os voltamogramas cíclicos (VCs) foram registrados em meio aprótico (DMF + TBABF6), para se assemelhar ao ambiente lipofílico, típico de membranas celulares. Por outro lado, o meio prótico mimetiza regiões hidrofílicas das matrizes biológicas. Este trabalho descreve dois casos de investigações farmacoeletroquímicas bem-sucedidas. No primeiro caso, investigou-se o comportamento eletroquímico da LQB-118, uma pterocarpanoquinona antitumoral e parasiticida, com mecanismos de ação relacionados à formação de espécies reativas de oxigênio (EROs) e interação com DNA, entre outros. Estudou-se também as pterocarpanoquinonas derivadas da LQB-118, mais precisamente seus derivados clorado, bromado e nitrado. O voltamograma cíclico (VC) para a LQB-118, em meio aprótico, exibe, pelo menos, quatro ondas catódicas. As duas primeiras são relacionadas com a redução habitual de quinonas. A presença de ondas adicionais sugere a quebra de anel heterocíclico e a geração de sistemas redutíveis adicionais. Investigação espectroeletroquímica revelou o surgimento de novas bandas de absorção, as quais sugerem a formação do quinonametídeo (QM) transiente. O QM foi capturado com tiofenol. Além disso, experimentos eletroquímicos foram realizados na presença e na ausência de oxigênio para verificar a reatividade com oxigênio, após a redução de LQB-118 e seus derivados, com resultados positivos. Estudos com o sensor de ssDNA, em solução, mostrou interação positiva com LQB-118 e seus produtos eletrogerados. A interação de LQB-118 com CT-DNA também foi evidenciada através da técnica de quenching de fluorescência. No segundo caso, a voltametria cíclica foi utilizada para investigar o comportamento eletroquímico de selenoquinonas antitumorais. Os perfis obtidos confirmam a presença de dois centros redox individuais. Todos os compostos mostraram atividade eletroquímica nas regiões anódica e catódica dos VCs. Estudou-se também o comportamento dos compostos em meio prótico e foi observada a formação de selenóxidos. Métodos eletroquímicos se mostraram adequados para prever rearranjos estruturais, formação de adutos, geração de espécies reativas de oxigênio, no caso de pterocarpanquinonas e para explorar caminhos redox in vitro das outras séries, correlacionando-se aos estudos in vivo.

Submitted by Franciele Moreira (francielemoreyra@gmail.com) on 2017-09-13T16:28:44Z No. of bitstreams: 2 Dissertação - Evellyn Gonçalves de Souza - 2017.pdf: 2198173 bytes, checksum: 0e490bd8b1f7554afb334a3e27faf8ef (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-09-19T13:57:54Z (GMT) No. of bitstreams: 2 Dissertação - Evellyn Gonçalves de Souza - 2017.pdf: 2198173 bytes, checksum: 0e490bd8b1f7554afb334a3e27faf8ef (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-09-19T13:57:54Z (GMT). No. of bitstreams: 2 Dissertação - Evellyn Gonçalves de Souza - 2017.pdf: 2198173 bytes, checksum: 0e490bd8b1f7554afb334a3e27faf8ef (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-08-17 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Dengue is an endemic disease that causes wide concern both the health systems and to the patients. Thus, it is important that studies aiming at diagnoses faster and with possibility of field application can be developed for the medical intervention happens early, avoiding the worsening of the cases. Therefore, the aim of this work was to develop an electrochemical biosensor based on the use of aptamer as a bioelement for recognition on the surface of the boron doped diamond electrode (BDD) for the detection of each of the four serotypes of the dengue virus. Previously to the development of the biosensor, the dot-blot and apta-PCR techniques were used as validation methods for the interaction between aptamer B07 and target, the 5'UTR region present in the viral genome. The cyclic voltammetry technique was used in the analysis of redox reactions on the surface of the BDD electrode with and without modification of its surface with chitosan film. Ferrocene was used as the redox mediator and electroactive indicator of hybridization of the DNA strands formed in the sensor. The peaks of current indicated that the electrode with chitosan film modification on its surface presented greater stability. The redox compound had higher affinity for the double chains hybridized on the surface of the electrode, showing current values for DENV 1, 2, 3 and 4 of were 0.73; 0.69; 0.79 and 1.03 μA, respectively. These values were higher than the current found for the single-stranded aptamer (ssDNA), which was 0.62 μA, as well as for the current obtained from the aptamer hybridized with its complementary strand (dsDNA) whose value was 0.91 μA. Analyzes with time variations were performed showing a reduction in current values as a function of time, probably due to the reduction of the interaction of the electroactive material in the sensor. The aptasensor developed here showed good detection distinction between nucleic acid sequences, presenting potential for application in the detection of dengue virus. / A dengue é uma doença endêmica que causa grande preocupação tanto aos sistemas de saúde quanto aos pacientes. Dessa forma, é importante que estudos visando diagnósticos mais rápidos e com possibilidade de aplicação a campo possam ser desenvolvidos para que a intervenção médica possa ser precoce, evitando-se o agravamento dos casos. Neste sentido, buscou-se no presente trabalho desenvolver um biossensor eletroquímico baseado no uso de aptâmero como bioelemento reconhecedor na superfície do eletrodo de diamante dopado com boro (DDB) para a detecção de cada um dos quatro sorotipos do vírus da dengue. Previamente ao desenvolvimento do biossensor, as técnicas de dot-blot e apta-PCR foram utilizadas como métodos de validação da interação entre o aptâmero B07 e alvo, a região 5’UTR presente no genoma viral. A técnica de voltametria cíclica foi utilizada nas análises de reações redox na superfície do eletrodo DDB com e sem modificação de sua superfície com filme de quitosana. O composto ferroceno foi utilizado como mediador redox e indicador eletroativo de hibridização das cadeias de DNA formadas no sensor. Os picos de corrente indicaram que o eletrodo com modificação de filme de quitosana em sua superfície apresentou maior estabilidade, onde o composto redox teve maior afinidade pelas duplas cadeias hibridizadas na superfície do eletrodo, apresentando valores de correntes para DENV 1, 2, 3 e 4 de foram 0,73; 0,69; 0,79 e 1,03 μA, respectivamente. Esses valores foram superiores a corrente encontrada para o aptâmero em fita simples (ssDNA) que foi de 0,62 μA, assim como observada para corrente obtida do aptâmero hibridizado com sua fita complementar (dsDNA) cujo valor obtido foi de 0,91 μA. Análises com variações de tempo foram realizadas apresentando redução nos valores de correntes em função do tempo, provavelmente devido à redução da interação do material eletroativo no sensor. O aptasensor aqui desenvolvido apresentou boa detecção distinção entre sequências de ácidos nucleicos, apresentando potencial para aplicação na detecção do vírus da dengue.

Neste trabalho foi realizada a funcionalização de grafite sem prévio tratamento em condições de Fridel-Crafts. Considerando que a grafite não possui hidrogênio em sua estrutura, não se observa uma reação de substituição eletrofílica. Por outro lado, o trabalho mostra o papel da umidade presente no grafite na reação de funcionalização. Dessa forma, foi proposto um mecanismo para a reação com a participação da água adsorvida na grafite estabilizando o carbocátion formado. O grafite funcionalizado obtido na reação foi utilizado como material eletródico. Para a reação de funcionalização, quatro moléculas foram utilizadas: ácido ferrocenomonocarboxílico, cloreto de 4-nitrobenzoíla, cloreto de 3,5-dinitrobenzoíla e ácido 3,4-dinitrobenzóico. Para o estudo das condições ótimas da reação, utilizou-se diferentes potências de radiação no reator de micro-ondas, sendo que a extensão da funcionalização mostrou-se sensível à variação deste parâmetro. Para a caracterização dos materiais, utilizou-se voltametria cíclica e análise térmica (TG e DTA). Resultados de infravermelho e Ramam são apresentados no Apêndice A. Os resultados eletroquímicos mostraram que os materiais funcionalizados em maiores potências apresentaram maior corrente Faradaica, mas ao mesmo tempo, o material obtido foi mais resistivo. A diferença de potencial relacionada ao processo redox do ferroceno aumentou conforme a extensão da funcionalização, uma vez que um sobrepotencial é necessário devido ao fluxo iônico (para a manutenção da eletroneutralidade) relativo ao número de espécies envolvidas. Os resultados eletroquímicos também indicaram que a funcionalização do grafite com os nitro compostos foi baixa. A análise térmica evidenciou que a reação de funcionalização do grafite com o ferroceno resultou em materiais com 15% a 20% (m/m) de material ligado ao grafite. Os materiais funcionalizados a maiores potências apresentaram maior massa ligada ao grafite. A funcionalização com os nitro compostos resultou em materiais com menos de 3% (m/m) de composto ligado ao grafite. Os resultados das duas técnicas mostraram coerência na análise da extensão da funcionalização. O material funcionalizado com o ácido ferrocenomonocarboxilico foi o que apresentou os melhores resultados e propõe-se uma explicação para tal baseado no mecanismo de reação sugerido. Com o objetivo de melhor elucidar o mecanismo da reação, foram realizadas algumas reações na ausência de alguns reagentes. Por exemplo, quando tenta-se funcionalizar o material sem a presença de cloreto de alumínio ou sem a umidade natural do grafite, a reação não ocorre. / In this work natural graphite functionalization in Fridel-Crafts conditions is performed using a one-step microwave assisted reaction. Since there is no hydrogen in graphite structure, it is not possible to observe electrophilic substitution. On the other hand this work shows the role of the moisture present on graphite in the functionalization reaction under this condition. Therefore, a reaction mechanism with the participation of the water naturally adsorbed on graphite stabilizing the formed carbocation has been suggested. After the reaction, the functionalized graphite was used as electrode material. Four molecules were used to functionalize graphite: Ferrocene monocarboxylic acid, 4-nitrobenzoyl chloride, 3,5-dinitrobenzoyl chloride and 3,4-dinitrobenzoic acid. To study the optimal conditions of the reaction, the microwave radiation power was varied and the extent of the functionalization on graphite was sensitive to this parameter. Two techniques were used to characterize the materials, cyclic voltammetry and thermal analysis (TG and DTA). IR and Raman data are shown in appendix A. Electrochemical results have shown that the materials functionalized at higher microwave radiation power have higher Faradaic current, but are more resistive. The potential difference between the peaks of the redox process of ferrocene increased with the extent of functionalization. This occurs because an overpotencial is needed to compensate the ionic flux (in order to maintain the electroneutrality) related to the number of species involved. The electrochemical results also indicated that the extent of functionalization of graphite with the nitro compounds was low. The thermal analysis have shown that the functionalization of graphite with ferrocene lead to values between 15% to 20% (m/m) of compound in the material. The materials functionalized at higher microwave radiation power presented higher relative mass in the material. The reaction with the nitro compounds lead to less than 3% (m/m) of compound in the final material. The results of both techniques were coherent about the extent of functionalization. The material functionalized with ferrocene monocarboxylic acid showed the best results, and an explanation for that based on the reaction mechanism is suggested. In order to elucidate the reaction mechanism, some experiments were realized in absent of some reagents. When the reaction were carried out without aluminum chloride or with dried graphite, the reaction has not occurred.