Photogeneration of Charge Carriers in Organic Semiconductors

S nástupem komerční výroby organických solárních článků roste i zájem o detailní poznání základních elektronových procesů souvisejících s fotogenerací náboje, které umožní dosáhnout vyšší účinnosti fotovoltaické konverze. Tato práce se zabývá studiem fotogenerace nosičů náboje v organických polovodičích, především v -konjugovaných polymerních materiálech. První část práce popisuje současné poznatky o fotogeneraci nosičů náboje v polymerních solárních článcích. Následuje experimentální a výsledková část, která se věnuje studiu polymerních solárních článků připravených z elektron donorních polymerů MDMO-PPV, Tg-PPV, PCDTBT a PCBTDPP a elektron akceptorních derivátů fullerenu PC60BM a PC70BM. Výsledky práce jsou rozděleny do tří hlavních částí: 1) studium přenosu náboje mezi elektron donorním a elektron akceptorním materiálem optickými metodami, 2) studium přenosu náboje mezi elektron donorním a elektron akceptorním materiálem optoelektrickými metodami a 3) vývoj organických solárních článků na flexibilních substrátech, zabývající se z velké části depozičními metodami tenkých vrstev funkčních materiálů.The interest in the detail knowledge about elementary electronic processes during photogeneration of charge carriers, which allow achieving higher efficiency of organic solar cells, grows with advent of the commercial organic solar cells production. The thesis is focused on study of photogeneration of charge carriers in organic semiconductors, especially in -conjugated polymer materials. First part of the thesis summarized state of the art in studies of photogeneration of charge carriers in polymer solar cells. Subsequent experimental and results part are focused on study of polymeric solar cells prepared from electron donor polymers MDMO-PPV, Tg-PPV, PCDTBT and PCBTDPP and electron acceptor derivates of fullerenes PC60BM and PC70BM. Results of the thesis are divided in tree main parts: 1) study of charge transfer between electron donor and electron acceptor materials by optical methods, 2) study of charge transfer between electron donor and electron acceptor materials by optoelectrical methods and 3) development of organic solar cells on flexible substrates. The last part is focused largely on deposition methods of active materials thin layer.

Quantum dots: synthesis, functionalization and bioconjugation for biological applications

Dissertation presented to obtain the Ph.D degree in Engineering Sciences and TechnologyThe main goal of this Doctoral work was to develop a fluorescent biomarker to identify antigenic proteins associated with specific parasites. Although it is known that fluorescent techniques making use of standard organic dyes are widely used for this purpose, the development of a new method was proposed using nanotechnology; in particular the use of nano optical reporters also called quantum dots (QDs). In order to achieve this goal, the research work was divided into four main tasks: (1) synthesis and characterization of CdSe/ZnS core-shell QDs; (2) design of dihydrolipoic acid (DHLA) ligands appended to oligo and poly (ethylene) glycols (PEG) with different functional groups to generate biocompatible QDs; (3) bioconjugation of QDs to monoclonal antibodies based on sophisticated protocols and (4) some chemical and biological applications of the synthesized non-conjugated and conjugated nanoparticles.(...)This work was supported by Fundação para a Ciência e Tecnologia (FCT) through a PhD grant to Ana Sofia Miguel (SFRH/BD/40303/2007) and the grant # PEst-OE/EQB/LA0004/2011. This work was also supported by the national funded project NTec/SQA/0131/2007 from FC

Electrophoretic deposition of carbon nanotubes on silicon substrates

This dissertation research describes the feasibility study and investigation of Electrophoretic Deposition (EPD) of carbon nanotubes (CNTs) for applications in semiconductor research. In recent years, the EPD technique has been considered as an economical, room temperature, solution based wet coating technique for thin and thick CNT films on arbitrary substrates. In this study, fabrication of uniform coatings of acid-treated CNTs has been pursued on bare silicon substrates by EPD from aqueous and organic suspensions. Research endeavors are extended to examine EPD of CNTs on silicon substrates with various surface coatings such as metal (aluminum), insulator layers (silicon dioxide and silicon nitride) and self-assembled polar organosilane (APTES) molecules. Microstructural imaging, spectroscopic analysis and characterization of the morphology of the CNT films have also been reviewed in relation to the deposition parameters such as inter-electrode electric field, deposition duration and APTES concentration. For research and development involving advanced spectroscopic analysis, Surface Enhanced Raman Spectroscopy (SERS) studies have been conducted on horizontally aligned EPD fabricated porous CNT networks coated with silver nanoparticles (AgNPs). The acquired Raman spectra of AgNP-CNT hybrid nanostructures display significant enhancement in the Raman intensity values of Rhodamine6G (R6G) analyte by several orders of magnitude with respect to the reference sample. Improvement in the Raman signals has pushed the detection limit to as low as 1 × 10^-12 M. The experimental results, reported in this dissertation, thus establish the novelty of EPD in the fabrication of the AgNP coated porous CNT substrate for routine SERS analysis of different target analytes

Electrochemically controlled patterning for biosensor arrays.

Existe una demanda creciente de dispositivos de análisis multianalito, con aplicaciones potenciales en los campos de la biomedicina y biotecnología, así como en el ámbito industrial y ambiental. Para el desarrollo de estos dispositivos resulta esencial un buen control espacial durante la etapa de inmovilización de las biomoléculas de interés; cada una de ellas debe ser depositada de forma precisa sobre la superficie del sensor (por ejemplo, un transductor amperométrico), evitando solapamientos que puedan comprometer la especificidad del sistema. El objetivo de esta tesis es desarrollar diferentes métodos de patterning para la inmovilización selectiva de biomoléculas. El primer método consiste en la electrodeposición selectiva de nanopartículas de oro biofuncionalizadas para el desarrollo de biochips. Se trata de un método de patterning controlado electroquímicamente, en el que las nanopartículas de oro se modifican en primer lugar recubriéndolas con diversos enzimas y a continuación se electrodepositan selectivamente sobre la superficie de un electrodo. Como parte de esta metodología, se prepararon nanopartículas de oro biofuncionalizadas utilizando tres estrategias diferentes: a través del enlace dativo oro-tiol, por adsorción directa o mediante interacción electrostática siguiendo la técnica layer-by-layer (capa por capa). Para la funcionalización de las nanopartículas de oro se emplearon distintas biomoléculas, como los enzimas peroxidasa de rábano (HRP), glucosa oxidasa (GOX) y albúmina de suero bovino (BSA), y finalmente oligonucleótidos modificados con moléculas fluorescentes y grupos tiol. Las nanopartículas biofuncionalizadas fueron caracterizadas mediante técnicas de espectroscopía UV-visible, microscopía electrónica de transmisión (TEM) y medida del potencial zeta. Mediante espectroscopía UV-visible se observó un pico de resonancia de plasmón característico de las nanopartículas modificadas, relacionado con la estabilidad de la preparación. La medida del potencial zeta permitió la caracterización de las nanopartículas de oro modificadas capa por capa con polímero redox y enzimas. También se estudiaron los cambios en el potencial zeta de nanopartículas modificadas con BSA a distintos valores de pH. Tras la preparación de las partículas biofuncionalizadas, se llevaron a cabo estudios fundamentales de electrodeposición de nanopartículas de oro modificadas con BSA y un polímero redox, con el fin de analizar el efecto de varios parámetros: potencial aplicado, tiempo de deposición, distancia entre los electrodos, superficie del electrodo auxiliar y pH del medio. Para estudiar el comportamiento electrocatalítico de las nanopartículas modificadas una vez electrodepositadas, se llevaron a cabo experimentos utilizando coloides de oro modificados con HRP y GOX. A continuación se empleó esta metodología para el desarrollo de biochips, utilizando dos configuraciones diferentes. En la primera, se electrodepositaron nanopartículas de oro funcionalizadas con GOX y HRP y modificadas con un polímero redox sobre la superficie de un chip de electrodos interdigitados (IDE), consiguiendo eliminar por completo las repuestas no específicas. En la segunda configuración, las partículas se modificaron con una capa adicional de polímero redox, comprobando de nuevo la ausencia total de respuestas no específicas después de la electrodeposición. Esta método de patterning es genérico y puede utilizarse para la producción de diversos biochips. El segundo método de patterning también está basado en el control electroquímico, y consiste en la modificación de los electrodos con monocapas autoensambladas electroactivas cuya funcionalidad es modulable en función del potencial aplicado. En esta metodología, la monocapa electroactiva contiene grupos acetal que pueden ser desprotegidos selectivamente mediante la aplicación de un potencial en zonas específicas de la superficie del electrodo. De esta manera quedan expuestos en la superficie grupos aldehído activos, que pueden ser fácilmente conjugados con aminas primarias presentes en las biomoléculas de interés. Los enzimas GOX y HRP se usaron como proteínas modelo para comprobar la versatilidad de esta técnica. Su aplicabilidad para la fabricación de biochips se demostró con medidas amperométricas y medidas en tiempo real mediante resonancia de plasmón de superficie combinado con electroquímica (eSPR). La tercera metodología es también un sistema de patterning controlado electroquímicamente, pero en este caso se utiliza la inmovilización del 4,4-bipiridil como base para la creación de biochips. Se sintetizaron moléculas de 4,4-bipiridil funcionalizadas con grupos carboxílicos, que fueron caracterizadas electroquímicamente y a continuación conjugadas con las biomoléculas de interés para la creación de biochips. La selectividad de estos sistemas se demostró colorimétricamente, obteniéndose niveles mínimos de respuesta inespecífica. Por último, el cuarto de los métodos de patterning desarrollados está basado en la técnica de fotolitografía. Los enzimas glucosa oxidasa y sarcosina oxidasa se depositaron selectivamente junto con un polímero redox sobre la superficie de electrodos interdigitados utilizando un proceso de lift off, consiguiendo eliminar por completo las señales cruzadas o cross-talk. Como parte de esta metodología se optimizaron varios procedimientos de inmovilización de las biomoléculas, con el fin de seleccionar la estrategia más adecuada. También se llevaron a cabo ensayos con diferentes reactivos para eliminar la adsorción inespecífica. Finalmente, el sistema optimizado fue aplicado sobre IDEs fabricados mediante fotolitografía. Los sensores de glucosa y sarcosina respondieron de forma selectiva a sus respectivos sustratos, con ausencia total de cross-talk. La presente tesis está estructurada en 7 capítulos. En el Capítulo I se exponen las bases del desarrollo de biochips, métodos de patterning con control electroquímico, otros métodos de patterning selectivo y las técnicas de fotolitografía, así como un resumen de la tesis. El Capítulo 2 y 3 describe la síntesis de coloides de oro, la modificación con biomoléculas, los estudios de estabilidad y los estudios fundamentales de electrodeposición de las nanopartículas de oro modificadas sobre la superficie de los electrodos. En el Capítulo 4 se muestra la aplicación de la electrodeposición de nanopartículas de oro biofuncionalizadas para la creación de biochips. El Capítulo 5 describe la inmovilización selectiva de biomoléculas mediante la desprotección electroquímica de monocapas autoensambladas electroactivas. En el Capítulo 6 se muestra la síntesis, caracterización e inmovilización selectiva de derivados de 4,4- bipiridil funcionalizados con HRP. El Capítulo 7 describe el patterning selectivo en la escala micrométrica de dos oxidasas sobre un chip de electrodos interdigitados mediante fotolitografía. Finalmente, el Capítulo 8 resume las conclusiones y el trabajo futuro.There is an increasing demand of multianalyte sensing devices having potential applications in biomedical, biotechnological, industrial and environmental fields. A good spatial control during biomolecule deposition step is strictly necessary; each biomolecule has to be precisely deposited on the surface of the relevant sensor (eg., an amperometric transducer), avoiding mixing that can compromise the biosensor specificity. The aim of this thesis is to develop different patterning methods for the selective immobilization of biomolecules. The first method is selective electrodeposition of biofunctionalized Au nanoparticles for biosensor arrays. This is an electrochemically controlled patterning method where the Au nanoparticles modified by the enzymes initially and later the enzyme modified Au nanoparticles were electrodeposited selectively on the electrode surface. As a part of this methodology, initially biofunctionalized Au nanoparticles were prepared using three different approcahes. One is Au-thiol dative bonding, the second is direct adsorption and finally electrostatic layerby- layer approach. Different biomolecules like horse radish peroxidase(HRP), glucose oxidase (GOX), bovine serum albumin(BSA), and finally fluorescence labelled oilgonucleotide thiols were used to attch to the Au nanoparticles. Biofunctionalized Au nanoparticles were characterized by different techniques like zeta sizer, UV-Vis spectroscopy, transmission electron microscopy (TEM). UV-Vis spectroscopy showed the successfull modification of Au nanoparticles with a characterstic surface plasmon peak related to the stability. By using zeta sizer, layer-by-layer modification of the Au nanoparticles with redox polymer and enzymes were characterized successfully. Changes of the Au nanoparticles modified with BSA was characterised at different pH s by using the zeta sizer. After the preparation of biofunctionalized particles, some fundamental studies were done with electrodeposition of Au nanoparticles modified with medically important BSA, redox polymer to see how different parameters like potential, time of deposition, interelectrode distance, counter electrode sized, pH, effect the electrodeposition. As a part of these fundamental studies Au colloids modified with HRP and GOX were deposited for studying the electrocalaytic behaviour of the enzymes on the Au nanoparticles after electrodeposition. Later this methodology was applied for creating biosensor arrays by using two different approaches. In the first approach, GOX and HRP functionalized redox polymer modified Au nanoparticles were electrodeposited successfully on an interdigitated electrode (IDE) array with complete absence of non-specific response. In the second approach the particles were modified with an extra redox polymer layer and proved that there is complete absence of nonspecific response after electrodeposition. Moreover, this patterning methodology is generic and can be used for production of different biochips. The second method is another electrochemically controlled patterning method where the electrodes were immobilized with self assembled monolayers with electroactive functionalities which can be tunable with potentials. In this methodology, electroactive self-assembled monolayer contains an active ligand aldehyde which can be readily conjugated to the primary amine group of the biomolecule is protected in the form of acetal. Later when a active potential was applied to the underlying electrode surface, the acetal functionality is deprotected to reveal the aldehyde functionality which was further conjugated to the biomolecule. Two enzymes GOX, HRP were used as model proteins to prove the versatility of this technique. Amperometric as well as real time measurements proved the selective applicability of this technique for creation of biosensor arrays. The third methodology is also an electrochemically controlled patterning methodology where the special advantage of the electrochemically-controlled immobilization of the 4,4-bipyridyl was taken as base for the creation of biosensor arrays. In this methodology, carboxylic acid functionalised 4,4, bipyridyl molecules were synthesized and characterized by electrochemistry. Later the biomolecules were conjugated to these special molecules for the creation of sensor arrays. Proof of selectivity was shown using colourimetrically with minimal non-specific response. Finally in the fourth method which is based on the photolithography technique, two different oxidases GOX & SOX were patterned along with redox polymer selectively on an IDE array using the lift off process with complete absence of cross-talk. As a part of this methodology, different immobilization methods were optimized initially for checking the best optimisation strategy. Later different reagents were tried to optimise the best reagent that prevents the non-specific adsorption. Later this optimised system was applied on the pholithographically created IDE array. Sarcosine and glucose sensors responded selectively to their substrates with complete absence of cross talk. This thesis is structured in 7 chapters. Chapter 1 establishes to basics of the biosensor arrays, electrochemically controlled patterning methods, other selectively patterned methods, photolithography and summary of this thesis. Chapter 2 describes about the gold colloid synthesis, modification with the biomolecules, stability studies. Chapter 3 decribes fundamental studies of the electrodeposition of the functionalised Au nanoparticles on the electrode surface. Chapter 4 describes the application of the electrodeposition of the protein functionalised Au nanoparticles for the creation of biosensor arrays. Chapter 5 describes the selective immobilization of biomolecules through electrochemical deprotection of electroactive self-assembled monolayers. Chapter 6 describes the synthesis, characterization and selective immobilization of HRP functionalized 4,4-bipyridyl derivatives. Chapter 7 describes the selective microscale protein patterning of two oxidases on an IDE array through photolithography. Finally chapter 8 summarizes the conclusions and the future work

The Synthesis Of Graphene Films Via Graphene Oxide Reduction Using Green Tea

In recent years, graphene has emerged as the most promising nanomaterial for various potential applications especially in biomedical field owing to its unique two dimensional (2D) nanostructure and intriguing physicochemical properties. A simple method to produce graphene was developed by reducing graphene oxide (GO) using green tea polyphenol (GTP) in a batch reactor. The aforementioned method was non-detrimental to the environment, cost effective and scalable for high-volume production. The product of the reduction process was referred as reduced GO (RGO). The effects of weight ratio of GTP/GO and reaction temperature on the reduction of GO were examined in details. The ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR), thermogravimetric analysis (TGA) and the measurement of zeta potential as well as the electrophoretic mobility reveal that a successful reduction of GO and the preparation of stable RGO dispersion in aqueous media could be attained by performing the reduction reaction of GO with GTP at 90 ºC using a weight ratio of GTP/GO=1. In addition, the UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis show that the RGO prepared using GTP exhibits final position of absorption peak (271 nm) and intensity of sp2 carbon that almost similar to the RGO produced using hydrazine (N2H4) solution. This observation indicates that the effective reduction property of GTP as compared to the N2H4 solution as a standard reducing agent

Synthesis of poly(3-hexylthiophene) active layer with ZnO nanorods and AU nanoparticles for the fabrication of hybrid plasmonic solar cells

Purpose and method of study: In the present study, zinc oxide nanobars were synthesized by electrochemical method and poly(3-hexylthiophene) by template-assisted method, as well as gold nanoparticles by microwave. The three components were incorporated as part of a hybrid plasmonic solar cell, in two configurations: inverted ITO/ZnO/P3HT/Au and conventional ITO/P3HT/ZnO/Au. The nanobars and nanoparticles were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, UV-Vis spectroscopy and dynamic light scattering. The solar cells were characterized with the use of a solar simulator and a picoammeter. Conclusions and contributions: A methodology was developed to adhere polymer nanorods, vertically aligned, on ITO glass; subsequently, ZnO nanobars were formed on the polymer matrix. Two hybrid plasmonic solar cells were fabricated in which gold nanoparticles were used as cathode; the nanoparticles were incorporated into the hybrid layer of ZnO and P3HT by electrophoretic deposition, which is presented as an alternative to the deposit of conductive metals by thermal evaporation. The basic parameters of the conventional solar cell were Voc = 200 mV, Jsc = 1.09x10-7 mA/cm2 , FF of 30%, while those of the inverted solar cell were Voc = 400 mV, Jsc = 6.95x10- 8 mA/cm2 , FF of 28%, however, the efficiencies of both were null (in the order of 10-7), due to the little contact between the different components of the cell

USE OF HIGH SURFACE NANOFIBROUS MATERIALS IN MEDICINE

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Evaluation of the purity and dispersion of single walled carbon nanotubes as potential pharmaceutical excipients

Single walled carbon nanotubes (SWNTs) are considered potential biomedical materials because of their flexible structure, hollow interior for fluidic transport, propensity for functionalization of the exterior walls, and biocompatibility. Research into exploiting these properties has focused on SWNTs as building blocks for novel drug-delivery systems, dosage forms, and biomedical substrates. However, the use of the internal nanochannels as conduits for trans-membrane drug delivery has not been explored. This research was initially designed to explore the latter. It is postulated that due to their mechanical strength and the presence of an internal conduit, SWNTs can be used for nanofluidic transport. Using a magnetic field, the magnetically responsive SWNT are driven into intact stratum corneum, creating nanochannels, for trans-membrane drug delivery. Initial studies showed however that a bottleneck is the aggregation of SWNTs on the surface of stratum corneum. To achieve trans-membrane nanofluidic delivery, the SWNTs have to be well dispersed in an appropriate pharmaceutical medium, and the SWNT have to be of high purity. Similarly, the presence of impurities in SWNTs, and the dispersion state of these materials in pharmaceutical solvents may give an insight into the discrepancies in toxicity that is reported. The purity of five commercially available SWNTs (AP-SWNT and P2-SWNT, from Carbon Solutions Inc, HMS-SWNT from Helix Materials, and NA-SWNT from Nanostructured and Amorphous Materials Inc. and CT-SWNT from ChepTubes Inc.) were analyzed by raman and electron dispersive x-ray spectroscopy (EDS) spectroscopy. Secondly, the dispersion states of SWNTs in various pharmaceutical solvents were evaluated by ultraviolet (UV) spectroscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS), zeta potential, and Raman spectroscopy to identify potential agents for exfoliation of SWNTs in selected pharmaceutical solution. SWNTs were dispersed in various solvents (water, propylene glycol [PG], dimethylsulfoxide [DMSO], and ethanol) as well as in 0.1% w/v aqueous solutions of anionic, cationic and neutral surfactants at a SWNT concentration of 0.1 mg/mL. SWNT suspensions described as dispersed yielded an evenly coloured suspension with no visible precipitate. The most stable dispersions were obtained with the gemini surfactants, which were confirmed by SEM observation of exfoliated SWNTs. Zeta (î) potential measurements of the fully dispersed SWNTs showed typical values of greater than +30 mV, while non-dispersed samples were less than +20 mV. SEM images of the dispersed solution showed the presence of exfoliated SWNTs compared to the aggregated SWNT clusters observed in non-dispersed systems. Raman spectra of dispersed SWNTs showed G-band peak shifts (to higher wavelengths), confirming the presence of exfoliated SWNTs. Even though the purity of SWNT did not correlate with amount of SWNT in dispersion, exfoliation of bundled SWNTs was accompanied by an increase in UV absorbance of the dispersion, with maximum exfoliation determined by a relatively stable UV absorbance. As pharmaceutical excipients, we have demonstrated that gemini surfactants are suitable dispersing agents for SWNTs, and shown that the dispersion of SWNT for gemini surfactants (12-3-12) is achieved below the critical micelle concentration. The dispersion of SWNT bundles into individual strands is the first crucial step towards their use in biological systems as drug carriers