Le suivi de la viabilitié, la croissance et le métabolisme cellulaire des bactéries peut contribuer de manière significative au diagnostic précoce de la maladie, mais peut aussi aider à améliorer le rendement des produits bactériens dans des expériences industrielle ou à petite echelle. Les méthodes conventionnelles utilisées pour l'étude de la sensibilité des bactéries aux antibiotiques sont basées principalement sur la culture, une technique qui prend au moins 12 heures pour rendre un résultat. Ce retard conduit au surtraitement d'un large éventail d'infections par des antibiotiques à large spectre, ce qui est coûteux et peut conduire à l'apparition de résistance à ces antibiotiques précieux, tandis que la détection rapide d'une infection virale ou l'absence de bactéries pourrait prévenir de tels traitements et, dans le cas d'une infection bactérienne, l'identification de la sensibilité aux antibiotiques pourrait permettre l'utilisation d'antibiotiques à spectre étroit. Le projet décrit dans le présent document vise à surveiller les activités biologiques des bactéries vivantes immobilisées sur les surfaces biofonctionnalisées de microstructures composées de semi-conducteurs quantiques (QS). Le procédé dépend de la sensibilité de la photoluminescence (PL) émise par des semi-conducteurs à la perturbation du champ électrique induit par la charge électrique des bactéries immobilisées sur la surface de ces structures. Dans la première phase du projet, nous avons étudié une méthode innovante impliquant la surveillance par PL de l'effet de photocorrosion dans des hétérostructures GaAs/AlGaAs. Le maintien d'un équilibre entre la sensibilité et la stabilité du biocapteur dans l'environnement aqueux nous a permis de détecter Escherichia coli K12 dans des solutions salines tamponnées au phosphate (PBS) avec une limite de détection attrayante de 103 UFC/ml en moins de 2 heures. Suite à cette recherche, nous avons émis l'hypothèse que ces hétérostructures pourraient être utilisés pour développer une méthode à faible coût et quasiment en temps reel de la croissance et de la sensibilité des bactéries aux antibiotiques. L'un des éléments clés dans le développement de cette plate-forme de biocapteurs était de démontrer que le GaAs (001), normalement utilisé pour recouvrir les hétérostructures de GaAs/AlGaAs, ne nuira pas à la croissance des bactéries. Dans la deuxième phase du projet, nous avons exploré la capture et la croissance de E. coli K12 sur des surfaces nues et biofonctionnalisées de GaAs (001). Il a été déterminé que la couverture initiale et les taux de croissance de bactéries dépendent de l'architecture de biofonctionnalisation utilisée pour capturer les bactéries: les surfaces biofonctionnalisées avec d'anticorps présentaient une efficacité de capture significativement plus élevée. En outre, on a trouvé que pour des suspensions contenant des bactéries à moins de 105 UFC/ml, la surface des plaquettes de GaAs ne supportait pas la croissance des bactéries, quel que soit le type d'architecture de biofonctionnalisation. Dans la troisième phase du projet, nous avons suivi la croissance et la sensibilité aux antibiotiques de E. coli K12 et E. coli HB101. Tandis que la présence de bactéries retardaient d’apparition du maximum de PL, la croissance des bactéries retardaient encore plus ce maximum. Par contre, en presence d’antibiotiques efficaces, la croissance des bactéries était arrêtée et le maximum de PL est arrivé plus tôt. Ainsi, nous avons pu distinguer entre des E. coli sensibles ou résistantes à la pénicilline ou à la ciprofloxacine en moins de 3h. En raison de la petite taille, du faible coût et de la réponse rapide du biocapteur, l'approche proposée a le potentiel d'être appliquée dans les laboratoires de diagnostic clinique pour le suivi rapide de la sensibilité des bactéries aux antibiotiques. / Abstract : Monitoring the viability, growth and cellular metabolism of bacteria can contribute significantly to the early diagnosis of disease, but can also help improve yield of bacterial products in industrial- or small-scale experiments. Conventional methods applied for investigation of antibiotic sensitivity of bacteria are mostly culture-based techniques that are time-consuming and take at least 12 h to reveal results. This delay leads to overtreatment of a wide range of infections with broad spectrum antibiotics which is costly and may lead to the development of resistance to these precious antibiotics, whereas rapid detection of a viral infection or absence of bacteria could prevent such treatments and, in the case of bacterial infection, identification of antibiotic susceptibility could allow use of narrow spectrum antibiotics. The project outlined in this document aims at monitoring biological activities of live bacteria immobilized on biofunctionalized surfaces of quantum semiconductor (QS) microstructures. The method takes advantage of the sensitivity of photoluminescence (PL) emitting semiconductors to the perturbation of the electric field induced by the electric charge of bacteria immobilized on the surface of these structures. Our hypothesis was that bacteria growing on the surface of biofunctionalized QS biochips would modify their PL in a different, and measurable way in comparison with inactivated bacteria. In the first phase of the project, we investigated an innovative method involving PL monitoring of the photocorrosion effect in GaAs/AlGaAs heterostructures. Maintaining the balance between device sensitivity and stability in the biosensing (aqueous) environment allowed us to detect Escherichia coli K12 in phosphate buffered saline solutions (PBS) at an attractive limit of detection of 103 CFU/mL in less than 2 hours. Following this research, we hypothesised that these heterostructures could be employed to develop a method for inexpensive and quasi-real time monitoring of the growth and antibiotic susceptibility of bacteria. One of the key elements in the development of this biosensing platform was to demonstrate that GaAs (001), normally used for capping PL emitting GaAs/AlGaAs heterostructures, would not inhibit the growth of bacteria. In the second phase of the project, we explored the capture and growth of E. coli K12 on bare and biofunctionalized surfaces of GaAs (001). It has been determined that the initial coverage, and the subsequent bacterial growth rates are dependent on the biofunctionalization architecture used to capture bacteria, with antibody biofunctionalized surfaces exhibiting significantly higher capture efficiencies. Moreover, for suspensions containing bacteria at less than 105 CFU/mL, it has been found that the surface of GaAs wafers could not support the growth of bacteria, regardless of the type of biofunctionalization architecture. In the third phase of the project, we used PL to monitor the growth and antibiotic susceptibility of E. coli K12 and E. coli HB101 bacteria. While immobilization of bacteria on the surface of GaAs/AlGaAs heterostructures retards the PL monitored photocorrosion, growth of these bacteria further amplifies this effect. By comparing the photocorrosion rate of QS wafers exposed to bacterial solutions with and without antibiotics, the sensitivity of bacteria to the specific antibiotic could be determined in less than 3 hours. Due to the small size, low cost and rapid response of the biosensor, the proposed approach has the potential of being applied in clinical diagnostic laboratories for quick monitoring of antibiotic susceptibility of different bacteria.

The objective of this study was to investigate photocatalytic water splitting over ordered TiO2 nanotube arrays. Synthesis of ordered nanotube arrays of titania, as a micron thick film on a titanium foil was accomplished by electrochemical anodization methods defined in the literature. Effect of two types of electrolyte (aqueous and organic) on the micro-morphology was observed by scanning electron microscopy. Optimum anodization times for the TiO2 nanotube electrodes, synthesized in ethylene glycol electrolyte, were different for acidic and basic electrolytes. Optimum times were determined as 2 hours in acidic and 4 hours in basic solutions. An H-type cell was constructed using a two side anodized titanium foil aiming the photocatalytic, stoichiometric and separate evolution of H2/O2 from the splitting of water. Gas evolution was observed at a rate of approximately 1 mL/h in the anode and 0.5 mL/h in the cathode, which implied the reverse of the desired stoichiometry. As the surface was corroded in that experimental conditions, electrochemical properties of the synthesized films were investigated by cyclic voltammetry (CV) at milder conditions. CV showed the reduction of Ti4+ to Ti3+, beginning at -0.2 V (vs. Ag/AgCl). Since the process is accompanied by proton intercalation to the oxide, non-annealed samples showed higher currents in that region. Non-annealed samples showed no photocurrent. Photocurrents obtained in this work, on the average 0.1-0.2 mA/cm2, were one order of magnitude lower than the similar studies in the literature.

Unconventional nanofabrication techniques; both those which have been newly developed and those under development, had brought inexpensive, facile, yet high quality means to fabricate nanostructures that have feature sizes of less than 100 nm in industry and academia. This dissertation focuses on developing unconventional fabrication techniques, building studying platforms, and studying the mechanisms behind them. The studies are divided into two main facets and four chapters. The first facet, in Chapter II and Chapter III, deals with the research and development of different nanofabrication techniques and nanostructures. These techniques include litho-synthesis, colloidal lithography, and photolithography. The nanostructures that were fabricated by these techniques include the metal nanoparticle arrays, and the self-assembled CdSe nanoring arrays. At the same time, the dissertation provides mechanisms and models to describe the physical and chemical nature of these techniques. The second area of this study, in Chapter III to Chapter V, presents the applications of these nanostructures in fundamental studies, i.e. the mechanisms of plasmon enhanced fluorescence and photo-oxidation kinetics of CdSe quantum dots, and applications such as molecular sensing and material fabrication. More specifically, these applications include tuning the optical properties of CdSe quantum dots, biomodification of CdSe quantum dots, and copper ion detection using plasmon and photo enhanced CdSe quantum dots. We have successfully accomplished our research goals in this dissertation. Firstly, we were able to tune the emission wavelength of quantum dots, blue-shifted for up to 45 nm, and their surface functionalization with photo-oxidation. A kinetic model to calculate the photo-oxidation rates was established. Secondly, we established a simple mathematical model to explain the mechanism of plasmon enhanced fluoresce of quantum dots. Our calculation and experimental data support the fluorescence resonance energy transfer (FRET) mechanism between quantum dots and the metal nanoparticles. Thirdly, we successfully pattered the CdSe quantum dots (diameter ~4 nm) into nanorings with tunable diameters and annular sizes on different substrates. We also established a physical model to quantitatively explain the mechanism with the forces that involved in the formation of the nanorings.

Orientadores: Cláudia Longo, Fernando Aparecido Sígoli / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-16T16:48:28Z (GMT). No. of bitstreams: 1 Silva_EversonThiagoSantosGeroncioda_M.pdf: 49355375 bytes, checksum: f552e7ceab4da2e918af08e239a6a01d (MD5) Previous issue date: 2010 / Resumo: O óxido de zinco é um semicondutor tipo-n que apresenta fotoatividade apenas sob radiação UV. Com o objetivo de aproveitar a radiação visível, investigou-se a incorporação de enxofre como dopante em amostras preparadas através da decomposição térmica de ZnS em atmosfera oxidante. O aquecimento de ZnS a 900°C por 30 minutos resultou em ZnO, um pó branco com estruttura de wurtzita, área de superfície de 6 m/g e energia de band gap Eg de 3,07 e 3,04 eV foram obtidas após 30 e 60 minutos a 620 °C; com coloração amarelada e estrutura de wurtzita, apresentaram área superficial de 17m/g. As propriedades eletroquímicas, investigadas em solução aquosa de Na2SO4 para eletrodos de filmes porosos depositados em vidro-FTO, indicaram comportamento de semicondutor tipo-n; sob irradiação com simulador solar, o potencial de circuito aberto negativo, VOC ~ -0,2 V, se manteve estável enquanto a fotocorrente positiva, inicialmente 120 mA cm, diminuiu gradativamente até 6 mA cm, diminuiu gradativamente até 6 mA cm após 4 horas sob irradiação. A baixa estabilidade pode ser atribuída à baixa adesão dos filmes no vidro-FTO e à fotocorrosão do semicondutor. Identificou-se a presença de íons Zn na solução, observou-se que a luz intensifica a dissolução dos óxidos em meio aquoso e que o ZnO é menos suscetível à fotocorrosão. Os eletrodos de ZnO e S:ZnO foram sensibilizados por corante de rutênio e utilizados na montagem de células solares. Os maiores valores de eficiência de conversão de luz em eletricidade, h, foram obtidos para células de 0,25 cm preparadas com eletrodos sensibilizados por 20 minutos e eletrólito líquido; as células de S:ZnO apresentaram corrente de curto circuito de 3,3 mA cm, VOC de 0,7 V e h ~ 1,0%, enquanto que as células de ZnO apresentaram valor similar de VOC, fotocorrente máxima de 0,76 mA/cm e h ~ 0,1%. Em comparação com as células de ZnO, a maior eficiência das células preparadas com ambas as amostras de S:ZnO pode estar relacionada à maior área de superfície e estabilidade mecânica destes filmes quando comparados aos de ZnO. Os estudos também foram realizados para células de S:ZnO preparadas sem o corante; o dispositivo apresentou VOC = 0,53 V, fotocorrente de 0,13 mA/cm e h ~ 0,04%. Embora o S:ZnO apresente Eg de 3,04 eV, com absorção em l < 410 nm, a eficiência de conversão é inferior à obtida na célula com do semicondutor sensibilizado com o corante. Os estudos revelaram que o S:ZnO pode ser utilizado em células solares, porém, devido à fotocorrosão, é necessário investigar meios para aumentar sua estabilidade para que não comprometa a durabilidade dos dispositivos para conversão de energia solar / Abstract: Zinc oxide is an n-type semiconductor that shows photoactivity under UV radiation. Aiming to decrease the zinc oxide band gap and consequently shift its absorption band to visible range of the electromagnetic spectrum, this work has investigated some physical chemical properties of sulfur containing zinc oxide (S:ZnO) samples. The S:ZnO samples were prepared by thermal decomposition of ZnS in oxidizing atmosphere. The heating of ZnS at 900°C for 30 minutes resulted in ZnO, a white powder with wurtzite structure with a surface area of 6 m/g and band gap energy Eg of 3.21 eV. Samples of S:ZnO, obtained by thermal treatment at 620°C for 30 and 60 minutes, have a band gap of 3.04 and 3.07 eV, respectively, yellowish color, wurtzite structure and surface area of 17 m/g. The electrochemical properties were investigated in Na2SO4 aqueous solution for porous film electrodes deposited on FTO-glass. All samples were characterized as an n-type semiconductor; under irradiation with solar simulator. The open potential circuit is negative, VOC ~ -0.2 V and remains stable while the positive photocurrent, initially 120 mA cm, gradually decreases to 6 mA cm after 4 hours of irradiation. The low stability may be attributed to poor adherence of the films on FTO-glass and to photocorrosion of the semiconductor in aqueous medium. The photocorrosion process was confirmed by presence of Zn ion in solution after the irradiation period. It was also observed that the light enhances the dissolution of S:ZnO samples in aqueous solution and that the sulfur free ZnO is less susceptible to the photocorrossion processes. The electrodes of ZnO and S:ZnO samples were sensitized by the ruthenium dye and tested as solar cells. The highest value of conversion efficiency of the light into electricity, h, was obtained for S:ZnO (Eg = 3,04 eV) solar cell that was prepared with 0.25 cm electrodes sensitized by 20 minutes using a liquid electrolyte. Solar cells prepared with S:ZnO (Eg = 3,04 eV) shows short-circuit current of 3.3 mA/cm, VOC of 0.7 V and h ~ 1.0%, while the cells of ZnO showed similar value of VOC, the maximum photocurrent of 0.76 mA/cm and h ~ 0.1%. Compared with the cells of ZnO, the better efficiency of the cells prepared from both S:ZnO samples may be related to the higher surface area and mechanical stability of these films when compared to undoped ZnO. Studies were also conducted for S:ZnO cells prepared without the dye. The prepared device shows VOC = 0.53 V, ISC = 0.13 mA/cmof photocurrent and h ~ 0.04%. Even though the S:ZnO presents a a low band gap value (Eg = 3.04 eV) and absorption at 410 nm, the conversion efficiency is lower than that obtained in dye sensitized cells. Studies revealed that the S:ZnO can be used in solar cells, however, an improvement of its photostability is necessary in order to enhances the durability of the devices applied in conversion of solar energy / Mestrado / Físico-Química / Mestre em Química

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