A biomimetic model membrane system on oxidic surfaces designed for the investigation of cytochrome c oxidase and other membrane proteins by fluorescence and waveguide spectroscopy

Die transmembrane Potenzialdifferenz Δφm ist direkt mit der katalytischen Aktivität der Cytochrom c Oxidase (CcO) verknüpft. Die CcO ist das terminale Enzym (Komplex IV) in der Atmungskette der Mitochondrien. Das Enzym katalysiert die Reduktion von O2 zu 2 H2O. Dabei werden Elektronen vom natürlichen Substrat Cytochrom c zur CcO übertragen. Der Eleltronentransfer innerhalb der CcO ist an die Protonentranslokation über die Membran gekoppelt. Folglich bildet sich über der inneren Membrane der Mitochondrien eine Differenz in der Protonenkonzentration. Zusätzlich wird eine Potenzialdifferenz Δφm generiert.rnrnDas Transmembranpotenzial Δφm kann mit Hilfe der Fluoreszenzspektroskopie unter Einsatz eines potenzialemfindlichen Farbstoffs gemessen werden. Um quantitative Aussagen aus solchen Untersuchungen ableiten zu können, müssen zuvor Kalibrierungsmessungen am Membransystem durchgeführt werden.rnrnIn dieser Arbeit werden Kalibrierungsmessungen von Δφm in einer Modellmembrane mit inkorporiertem CcO vorgestellt. Dazu wurde ein biomimetisches Membransystem, die Proteinverankerte Doppelschicht (protein-tethered Bilayer Lipid Membrane, ptBLM), auf einem transparenten, leitfähigem Substrat (Indiumzinnoxid, ITO) entwickelt. ITO ermöglicht den simultanen Einsatz von elektrochemischen und Fluoreszenz- oder optischen wellenleiterspektroskopischen Methoden. Das Δφm in der ptBLM wurde durch extern angelegte, definierte elektrische Spannungen induziert. rnrnEine dünne Hydrogelschicht wurde als "soft cushion" für die ptBLM auf ITO eingesetzt. Das Polymernetzwerk enthält die NTA Funktionsgruppen zur orientierten Immobilisierung der CcO auf der Oberfläche der Hydrogels mit Hilfe der Ni-NTA Technik. Die ptBLM wurde nach der Immobilisierung der CcO mittels in-situ Dialyse gebildet. Elektrochemische Impedanzmessungen zeigten einen hohen elektrischen Widerstand (≈ 1 MΩ) der ptBLM. Optische Wellenleiterspektren (SPR / OWS) zeigten eine erhöhte Anisotropie des Systems nach der Bildung der Doppellipidschicht. Cyklovoltammetriemessungen von reduziertem Cytochrom c bestätigten die Aktivität der CcO in der Hydrogel-gestützten ptBLM. Das Membranpotenzial in der Hydrogel-gestützten ptBLM, induziert durch definierte elektrische Spannungen, wurde mit Hilfe der ratiometrischen Fluoreszenzspektroskopie gemessen. Referenzmessungen mit einer einfach verankerten Dopplellipidschicht (tBLM) lieferten einen Umrechnungsfaktor zwischen dem ratiometrischen Parameter Rn und dem Membranpotenzial (0,05 / 100 mV). Die Nachweisgrenze für das Membranpotenzial in einer Hydrogel-gestützten ptBLM lag bei ≈ 80 mV. Diese Daten dienen als gute Grundlage für künftige Untersuchungen des selbstgenerierten Δφm der CcO in einer ptBLM.

Self-Assembled Monolayers (SAMs) in Organic Field-Effect Transistors

Organic printed electronics is attracting an ever-growing interest in the last decades because of its impressive breakthroughs concerning the chemical design of π-conjugated materials and their processing. This has an impact on novel applications, such as flexible-large-area displays, low- cost printable circuits, plastic solar cells and lab-on-a-chip devices. The organic field-effect transistor (OFET) relies on a thin film of organic semiconductor that bridges source and drain electrodes. Since its first discovery in the 80s, intensive research activities were deployed in order to control the chemico-physical properties of these electronic devices and consequently their charge. Self-assembled monolayers (SAMs) are a versatile tool for tuning the properties of metallic, semi-conducting, and insulating surfaces. Within this context, OFETs represent reliable instruments for measuring the electrical properties of the SAMs in a Metal/SAM/OS junction. Our experimental approach, named Charge Injection Organic-Gauge (CIOG), uses OTFT in a charge-injection controlled regime. The CIOG sensitivity has been extensively demonstrated on different homologous self-assembling molecules that differ in either chain length or in anchor/terminal group. One of the latest applications of organic electronics is the so-called “bio-electronics” that makes use of electronic devices to encompass interests of the medical science, such as biosensors, biotransducers etc… As a result, thee second part of this thesis deals with the realization of an electronic transducer based on an Organic Field-Effect Transistor operating in aqueous media. Here, the conventional bottom gate/bottom contact configuration is replaced by top gate architecture with the electrolyte that ensures electrical contact between the top gold electrode and the semiconductor layer. This configuration is named Electrolyte-Gated Field-Effect Transistor (EGOFET). The functionalization of the top electrode is the sensing core of the device allowing the detection of dopamine as well as of protein biomarkers with ultra-low sensitivity.

Stimuli-responsive materials for self-healing in corrosion protection

The corrosion of metallic materials is a crucial issue on an economical and ecological scale. Corrosion protection becomes then necessarily needed. The main focus of the thesis is to develop stimuli-responsive nanocontainers for self-healing in corrosion protection. A nanocontainer is efficient if distinct payloads can be selectively released via different stimuli because unwanted and unspecific release can be avoided. For anti-corrosion, the wanted nanocontainer is the one able to release its self-healing agents or corrosion inhibitors upon change of pH- or/and redox-potential due to the variation of these two signals at the corroded sites. Conducting polymers such as polyaniline (PANI) were chosen for building the shell of capsules due to their important characteristics of being both pH- and redox responsive.

Electronic properties of zig-zag carbon nanotubes : a first-principles study

Carbon nanotube (CNT) is a one dimensional (1-D) nanostructured material, which has been the focal point of research over the past decade for intriguing applications ranging from nanoelectronics to chemical and biological sensors. Using a first-principles gradient corrected density functional approach, we present a comprehensive study of the geometry and energy band gap in zig-zag semi-conducting (n,0) carbon nanotubes (CNT) to resolve some of the conflicting findings. Our calculations confirm that the single wall (n,0) CNTs fall into two distinct classes depending upon n mod 3 equal to 1 (smaller band gaps) or 2 (larger gaps). The effect of longitudinal strain on the band gap further confirms the existence of two distinct classes: for n mod 3 = 1 or 2, changing Eg by ~ ±110 meV for 1% strain in each case. We also present our findings for the origin of metallicity in multiwall CNTs.

MAGNETO-PHOTONIC CRYSTALS FOR OPTICAL SENSING APPLICATIONS

Among the optical structures investigated for optical sensing purpose, a significant amount of research has been conducted on photonic crystal based sensors. A particular advantage of photonic crystal based sensors is that they show superior sensitivity for ultra-small volume sensing. In this study we investigate polarization changes in response to the changes in the cover index of magneto-optic active photonic band gap structures. One-dimensional photonic-band gap structures fabricated on iron garnet materials yield large polarization rotations at the band gap edges. The enhanced polarization effects serve as an excellent tool for chemical sensing showing high degree of sensitivity for photonic crystal cover refractive index changes. The one dimensional waveguide photonic crystals are fabricated on single-layer bismuth-substituted rare earth iron garnet films ((Bi, Y, Lu)3(Fe, Ga)5O12 ) grown by liquid phase epitaxy on gadolinium gallium garnet substrates. Band gaps have been observed where Bragg scattering conditions links forward-going fundamental waveguide modes to backscattered high-order waveguide modes. Large near-band-edge polarization rotations which increase progressively with backscattered-mode order have been experimentally demonstrated for multiple samples with different composition, film thickness and fabrication parameters. Experimental findings are supported by theoretical analysis of Bloch modes polarization states showing that large near stop-band edge rotations are induced by the magneto-photonic crystal. Theoretical and experimental analysis conducted on polarization rotation sensitivity to waveguide photonic crystal cover refractive index changes shows a monotonic enhancement of the rotation with cover index. The sensor is further developed for selective chemical sensing by employing Polypyrrole as the photonic crystal cover layer. Polypyrrole is one of the extensively studied conducting polymers for selective analyte detection. Successful detection of aqueous ammonia and methanol has been achieved with Polypyrrole deposited magneto-photonic crystals.

Nanometer-size anisotropy of injection-molded polymer micro-cantilever arrays

Understanding and controlling the structural anisotropies of injection-molded polymers is vital for designing products such as cantilever-based sensors. Such micro-cantilevers are considered as cost-effective alternatives to single-crystalline silicon-based sensors. In order to achieve similar sensing characteristics,structure and morphology have to be controlled by means of processing parameters including mold temperature and injection speed. Synchrotron radiation-based scanning small- (SAXS) and wide-angle x-ray scattering techniques were used to quantify crystallinity and anisotropy in polymer micro-cantilevers with micrometer resolution in real space. SAXS measurements confirmed the lamellar nature of the injection-molded semi-crystalline micro-cantilevers. The homogenous cantilever material exhibits a lamellar periodicity increasing with mold temperature but not with injection speed. We demonstrate that micro-cantilevers made of semi-crystalline polymers such as polyvinylidenefluoride, polyoxymethylene, and polypropylene show the expected strong degree of anisotropy along the injection direction.

Polipirrol, un buen soporte para electrodos de pilas de combustible de metanol directo (DMFC)

(SPA) El polipirrol es uno de los polímeros conductores más utilizados en la preparación de electrodos debido a su alta actividad catalítica para la oxidación y reducción del metanol. En este trabajo se ha depositado electroquímicamente polipirrol a diferentes potenciales de depósito, Ed, sobre tela de carbón no tejida Freudenberg en medio ácido. Se ha analizado la morfología y la respuesta electroquímica en medio HClO4 y en presencia de HClO4+MeOH antes y después de la síntesis del polipirrol sobre ella. Lastructura de las películas obtenidas se ha estudiado por espectroscopia infrarroja de transformada de Fourier, FTIR. Se observa que el polipirrol mejora las propiedades electroquímicas de la tela de carbón, obteniéndose el mejor resultado para su aplicación como soporte del catalizador en pilas de combustible con la película sintetizada a 1,0V. (ENG) Polypyrrole is one of the most used conducting polymers in electrode building due to its high catalytic activity to the methanol oxidation and reduction. By this motive, polypyrrole has been electrochemically synthesized at constant potential, Ed, on Freudenberg carbon cloth in acid medium. Carbon cloth morphology and electrochemical behaviour in HClO4 and in HClO4+MeOH before and after the polypyrrole eposition have been analysed. The structure of the films was studied by Fourier transform infrared spectroscopy, FTIR. The polypyrrole improves the electrochemical properties of the studied carbon cloth. The biggest charge of the electroactive area is the one synthesized at 1.0V, being the best for its application as catalyst support in fuel cells.

Polímeros condutores aplicados a sistemas-modelo de liberação controlada eletroquimicamente de drogas

Este trabalho descreve a síntese, caracterização e aplicação de sistemas poliméricos baseados em polímeros condutores em sistemas de liberação controlada de drogas. Esta tese pode ser dividida em duas partes: na primeira se apresentam os resultados da aplicação de filmes de polianilina e polipirrol na liberação de drogasmodelo como a dopamina protonada e o ácido salicílico. Na liberação de salicilato utilizou-se um filme polianilina eletrosintetizado e dopado com íons cloreto. Já para a liberação de dopamina protonada (um cátion) a liberação foi conduzida a partir de um sistema bicamadas, com um filme de polianilina recoberta com uma camada de Náfion. É mostrada a liberação controlada nos dois casos, porém também se discutem limitaçãoes deste tipo de sistema que levaram ao estudo de uma forma alternativa de controle eletroquímico utilizando polímeros condutores. A segunda parte do trabalho mostra então esta nova metodologia que se baseia em compósitos de poianilina eletropolimerizada no interior de hidrogéis de poliacrilamida. É mostrado que este novo material é eletroativo e mantém as características de intumescimento dos hidrogéis, tanto necessárias ao desenvolvimento destes sistemas de liberação controlada. Mecanismos para o crescimento e distribuição da polianilina na matriz isolante e para a atuação do compósito no controle eletroquímico da liberação são propostos com base nos dados de microscopia de força atômica, Raman e eletrônica de varredura, além de testes de liberação controlada com moléculas de diferentes cargas.

Effect of the intercalated cation-exchanged on the properties of nanocomposites prepared by 2-aminobenzene sulfonic acid with aniline and montmorillonite

Polymer/montmorillonite nanocomposites were prepared. Intercalation of 2-aminobenzene sulfonic acid with aniline monomers into montmorillonite modified by cation was followed by subsequent oxidative polymerization of monomers in the interlayer spacing. The clay was prepared by cation exchange process between sodium cation in (M–Na) and copper cation (M–Cu). XRD analyses show the manifestation of a basal spacing (d-spacing) for M–Cu changes depending on the inorganic cation and the polymer intercalated in the M–Cu structure. TGA analyses reveal that polymer/M–Cu composites is less stable than M–Cu. The conductivity of the composites is found to be 103 times higher than that for M–Cu. The microscopic examinations including TEM picture of the nanocomposite demonstrated an entirely different and more compatible morphology. Remarkable differences in the properties of the polymers have also been observed by UV–Vis and FTIR, suggesting that the polymer produced with presence of aniline has a higher degree of branching. The electrochemical behavior of the polymers extracted from the nanocomposites has been studied by cyclic voltammetry which indicates the electroactive effect of nanocomposite gradually increased with aniline in the polymer chain.

Superconductivity in metal-mixed ion-implanted polymer films

Ion implantation of normally insulating polymers offers an alternative to depositing conjugated organics onto plastic films to make electronic circuits. We used a 50 keV nitrogen ion beam to mix a thin 10 nm Sn/Sb alloy film into the subsurface of polyetheretherketone and report the low temperature properties of this material. We observed metallic behavior, and the onset of superconductivity below 3 K. There are strong indications that the superconductivity does not result from a residual thin film of alloy, but instead from a network of alloy grains coupled via a weakly conducting, ion-beam carbonized polymer matrix. (c) 2006 American Institute of Physics.

Intrinsically flexible electronic materials for smart device applications

A novel method to fabricate chemically linked conducting polymer–biopolymer composites that are intrinsically flexible and conducting for functional electrode applications is presented. Polypyrrole was synthesised in situ during the cellulose regeneration process using the 1-butyl-3-methylimidazolium chloride ionic liquid as a solvent medium. The obtained polypyrrole–cellulose composite was chemically blended and showed flexible polymer properties while retaining the electronic properties of a conducting polymer. Addition of an ionic liquid such as trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide, enhanced the flexibility of the composite. The functional application of these materials in the electrochemically controlled release of a model drug has been demonstrated. This strategy opens up a new design for a wide spectrum of materials for smart electronic device applications wherein the functionality of doping and de-doping of conducting polymers is retained and their processability issue is addressed by exploiting an ionic liquid route.

Development of functionalised multiwalled carbon nanotube/polyaniline composites for electrical applications

Combining intrinsically conducting polymers with carbon nanotubes (CNT) helps in creating composites with superior electrical and thermal characteristics. These composites are capable of replacing metals and semiconductors as they possess unique combination of electrical conductivity, flexibility, stretchability, softness and bio-compatibility. Their potential for use in various organic devices such as super capacitors, printable conductors, optoelectronic devices, sensors, actuators, electrochemical devices, electromagnetic interference shielding, field effect transistors, LEDs, thermoelectrics etc. makes them excellent substitutes for present day semiconductors.However, many of these potential applications have not been fully exploited because of various open–ended challenges. Composites meant for use in organic devices require highly stable conductivity for the longevity of the devices. CNT when incorporated at specific proportions, and with special methods contributes quite positively to this end.The increasing demand for energy and depleting fossil fuel reserves has broadened the scope for research into alternative energy sources. A unique and efficient method for harnessing energy is thermoelectric energy conversion method. Here, heat is converted directly into electricity using a class of materials known as thermoelectric materials. Though polymers have low electrical conductivity and thermo power, their low thermal conductivity favours use as a thermoelectric material. The thermally disconnected, but electrically connected carrier pathways in CNT/Polymer composites can satisfy the so-called “phonon-glass/electron-crystal” property required for thermoelectric materials. Strain sensing is commonly used for monitoring in engineering, medicine, space or ocean research. Polymeric composites are ideal candidates for the manufacture of strain sensors. Conducting elastomeric composites containing CNT are widely used for this application. These CNT/Polymer composites offer resistance change over a large strain range due to the low Young‟s modulus and higher elasticity. They are also capable of covering surfaces with arbitrary curvatures.Due to the high operating frequency and bandwidth of electronic equipments electromagnetic interference (EMI) has attained the tag of an „environmental pollutant‟, affecting other electronic devices as well as living organisms. Among the EMI shielding materials, polymer composites based on carbon nanotubes show great promise. High strength and stiffness, extremely high aspect ratio, and good electrical conductivity of CNT make it a filler of choice for shielding applications. A method for better dispersion, orientation and connectivity of the CNT in polymer matrix is required to enhance conductivity and EMI shielding. This thesis presents a detailed study on the synthesis of functionalised multiwalled carbon nanotube/polyaniline composites and their application in electronic devices. The major areas focused include DC conductivity retention at high temperature, thermoelectric, strain sensing and electromagnetic interference shielding properties, thermogravimetric, dynamic mechanical and tensile analysis in addition to structural and morphological studies.

Synthesis, Characterization and Properties of Conductive Elastomeric Composites Based on Polypyrrole and Short Nylon-6 Fiber

The search for new materials especially those possessing special properties continues at a great pace because of ever growing demands of the modern life. The focus on the use of intrinsically conductive polymers in organic electronic devices has led to the development of a totally new class of smart materials. Polypyrrole (PPy) is one of the most stable known conducting polymers and also one of the easiest to synthesize. In addition, its high conductivity, good redox reversibility and excellent microwave absorbing characteristics have led to the existence of wide and diversified applications for PPy. However, as any conjugated conducting polymer, PPy lacks processability, flexibility and strength which are essential for industrial requirements. Among various approaches to making tractable materials based on PPy, incorporating PPy within an electrically insulating polymer appears to be a promising method, and this has triggered the development of blends or composites. Conductive elastomeric composites of polypyrrole are important in that they are composite materials suitable for devices where flexibility is an important parameter. Moreover these composites can be moulded into complex shapes.

PEDOT:PSS thin films: Applications in Bioelectronics

Owing to their capability of merging the properties of metals and conventional polymers, Conducting Polymers (CPs) are a unique class of carbon-based materials capable of conducting electrical current. A conjugated backbone is the hallmark of CPs, which can readily undergo reversible doping to different extents, thus achieving a wide range of electrical conductivities, while maintaining mechanical flexibility, transparency and high thermal stability. Thanks to these inherent versatility and attracting properties, from their discovery CPs have experienced incessant widespread in a great plethora of research fields, ranging from energy storage to healthcare, also encouraging the spring and growth of new scientific areas with highly innovative content. Nowadays, Bioelectronics stands out as one of the most promising research fields, dealing with the mutual interplay between biology and electronics. Among CPs, the polyelectrolyte complex poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS), especially in the form of thin films, has been emphasized as ideal platform for bioelectronic applications. Indeed, in the last two decades PEDOT:PSS has played a key role in the sensing of bioanalytes and living cells interfacing and monitoring. In the present work, development and characterization of two kinds of PEDOT:PSS-based devices for applications in Bioelectronics are discussed in detail. In particular, a low-cost amperometric sensor for the selective detection of Dopamine in a ternary mixture was optimized, taking advantage of the electrocatalytic and antifouling properties that render PEDOT:PSS thin films appealing tools for electrochemical sensing of bioanalytes. Moreover, the potentialities of this material to interact with live cells were explored through the fabrication of a microfluidic trapping device for electrical monitoring of 3D spheroids using an impedance-based approach.

Non-invasive methodology for the identification of plastic pieces in museum environment – a novel approach

The preservation of modern and contemporary art and costume collections in museums requires a complete understanding of their constituent materials which are often synthetic or semi-synthetic polymers. An extraordinary amount of quality information can be gained from instrumental techniques, but some of them have the disadvantage of being destructive. This paper presents a new totally integrated non-invasive methodology, for the identification of polymers and their additives, on plastic artefacts in museums. NMR (nuclear magnetic resonance) and in-situ FTIR-ATR (attenuated total reflection infrared spectroscopy) combination allowed the full characterization of the structure of thesematerials and correct identification of each one. The NMR technique applied to leached surface exudates identified unequivocally a great number of additives, exceeding the Py–GC–MS analysis of micro-fragments in number and efficiency. Additionally, in-situ FTIR-ATR provided exactly the same information of the destructive μ-FTIR about the polymer structure and confirmed the presence of some additives. Eight costume pieces (cosmetic boxes and purses), dating to the beginning of the 20th century and belonging to the Portuguese National Museum of Costume and Fashion, were correctly identified with this new integrated methodology, as beingmade of plastics derived fromcellulose acetate or cellulose nitrate polymers, contradicting the initial information that these pieces were made of Bakelite. The identification of a surprisingly large number of different additives forms an added value of this methodology and opens a perspective of a quick and better characterization of plastic artefacts in museum environments.