<p>Tungsten trioxide is a material with a variety of application areas. For example, the material is used within thin film technologies as electrochromic material in smart windows, as electrochemically functional material in thermal control applications or as active layer in gas sensing application. Metal-oxide semiconductor gas sensors are of significant interest to detect toxic and hazardous gases. The use of small and cheep sensors is preferable since a large number of sensors easily can be placed at different sites to monitor the concentration of different species without involving huge investments.</p><p>In this work, WO₃ nanoparticle films were produced using an advanced gas deposition unit for gas sensing applications. The structure of the WO₃ nanoparticle films was determined using X-ray diffraction, neutron scattering, X-ray photoelectron spectroscopy, elastic recoil detection analysis and electron microscopy. The as deposited films consist of sub-stoichiometric WO₃ and exhibit a large degree of porosity, which together with the small particle size of about 5 nm results in a large surface area and therefore excellent prospects for gas sensor applications. </p><p>Investigations on the optical properties and temperature dependence of the resistance indicate hopping conduction in the WO₃ films. The bandgaps for tetragonal and monoclinic WO₃ were found to be direct, which is in accordance with band structure calculations.</p><p>Sensor properties were investigated using resistance measurements upon test gas exposures. The experiments were performed at fixed operating temperatures as well as on temperature modulated sensors. The films of WO₃ showed excellent sensitivity to H₂S gas and selectivity to other gases. The responses of temperature modulated sensors were further analyzed using mathematical transformations and pattern recognition methods whereby different gases could be distinguished.</p><p>We also present a sensing technique using conduction noise as a tool for detection of alcohol vapor. The relative change of the noise, due to the inserted alcohol, can be as large as two orders of magnitude. </p>

Advances in recent nanoscience technologies have generated a new compilation of biocompatible, fluorescent nanoparticles derived from semiconductor quantum dots (QDs). QDs are extremely small in size and possess very large surface areas, which gives them unique physical properties and applications distinct from those of bulk systems. When exposed to biological fluid, these QDs may become coated with proteins and other biomolecules given their dynamic nature. These protein-QD systems may affect or enhance the changes in protein structure and stability, leading to the destruction of biological function. It is believed that these QDs can act as nucleation centers and subsequently promote protein fibril formation. Protein fibrillation is closely associated with many fatal human diseases, including neurodegenerative diseases and a variety of systemic amyloidoses. This topic of protein-QD interaction brings about many key issues and concerns, especially with respect to the potential risks to human health and the environment. Herein, the behavioral effects of dihydrolipoic acid (DHLA)-capped CdSe/ZnS (core/shell) QDs in hen egg-white lysozyme (HEWL) and human serum albumin (HSA) protein systems were systematically analyzed. This study gives rise to a better understanding of the potentially useful application of these protein-QD systems in nanobiotechnology and nanomedicine as a bioimaging tool and/or as a reference for controlled biological self-assembly processes.

<p>In this thesis, I present the electrochemical studies of three dendrimeric polypropylene imine (PPI) nanomaterials and their applications as a platform in the development of a novel label free DNA nanobiosensor based on electrochemical impedance spectroscopy. Cyclic voltammetry (CV), differentia pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivities of the nanomaterials on glassy carbon electrode (GCE) as the working electrode.</p>

One important driving force in nanotechnology today is the change which can be made in the properties of a material when the dimensions of its individual building blocks are decreased below approximately 100 nm. Such small building blocks, typically nanoparticles, may induce new and unique properties compared to those of the corresponding bulk material. The challenge in nanotechnology is to make nanoparticles with a discrete particle size within the range 1-10 nm. It is also important to develop appropriate assembly methodologies in order to construct devices composed of such small building blocks. This thesis reports iron nanoparticle synthesis using laser-assisted photolysis of ferrocene. The particles were protected against oxidation by a carbon shell formed in situ during their growth. By varying the experimental conditions such as fluence, repetition rate and laser beam area, particles could be synthesized in the size range 1 to 100 nm. Their size was measured using a differential mobility analyser (DMA), transmission electron microscopy (TEM) and X-ray diffraction (XRD). DMA was also used successfully to size-select particles to facilitate the deposition of monodisperse nanoparticle films. A theoretical "residence time approach (RTA)" model was developed to relate particle volume to the laser parameters used. The growth of these particles was studied in situ using optical emission spectroscopy; the results were compared with those from quantum mechanical calculations. The particles were characterised ex situ by TEM, convergent beam electron diffraction, XRD, X-ray photoelectron spectroscopy and Raman spectroscopy. Results from the TEM investigations revealed that the carbon shell was graphitic close to the iron core, while the outer part of the carbon shell was amorphous, indicating different growth mechanisms. Both bcc and fcc iron particles were observed.

Electrical transport properties of nanoparticle gold films made by the gas evaporation method were analysed using resistivity measurements. Low temperature electrical transport measurements showed a cross-over from a temperature range dominated by inelastic scattering to a temperature range dominated by elastic scattering, presumably by grain boundaries. This cross-over shifted towards lower temperatures with increasing grain size. High temperature in-situ electrical transport measurements were carried out in isothermal annealing experiments. Four types of samples, prepared at different deposition rates, were analysed. Samples prepared at low deposition rate displayed a higher thermal stability than samples prepared at high deposition rate. A relaxation model was fitted to the in-situ electrical transport data. The model included an activation energy, which was found to increase with increasing annealing temperature for all samples, thus pointing at the presence of pinning mechanisms in the samples. Optical properties of nanoparticle gold films were investigated in the 0.3 &lt; λ &lt; 12.5 µm wavelength range. A model taking grain boundary scattering into account was successfully fitted to the experimental data and it was shown that the infrared reflectance decreased with decreasing grain size as a consequence of increased grain boundary scattering. Nanoparticle tin-doped indium oxide films were made by spin-coating a dispersion containing the nanoparticles onto a substrate. The tin-doped indium oxide particles were prepared by a wet-chemical method. Optical properties were investigated in the 0.3 &lt; λ &lt; 30 µm wavelength range by reflectance and transmittance measurements. Effective medium theory was employed in the analyses of the optical data and information regarding film porosity and charge carrier concentration and mobility within the individual nanoparticles was obtained. It was found that ionized impurity scattering of the conduction electrons dominates within the particles. The temperature-dependent film resistivity was found to be governed by insulating barriers between clusters containing a large number of nanoparticles, thereby giving a negative temperature coefficient of resistivity.

Tungsten trioxide is a material with a variety of application areas. For example, the material is used within thin film technologies as electrochromic material in smart windows, as electrochemically functional material in thermal control applications or as active layer in gas sensing application. Metal-oxide semiconductor gas sensors are of significant interest to detect toxic and hazardous gases. The use of small and cheep sensors is preferable since a large number of sensors easily can be placed at different sites to monitor the concentration of different species without involving huge investments. In this work, WO3 nanoparticle films were produced using an advanced gas deposition unit for gas sensing applications. The structure of the WO3 nanoparticle films was determined using X-ray diffraction, neutron scattering, X-ray photoelectron spectroscopy, elastic recoil detection analysis and electron microscopy. The as deposited films consist of sub-stoichiometric WO3 and exhibit a large degree of porosity, which together with the small particle size of about 5 nm results in a large surface area and therefore excellent prospects for gas sensor applications. Investigations on the optical properties and temperature dependence of the resistance indicate hopping conduction in the WO3 films. The bandgaps for tetragonal and monoclinic WO3 were found to be direct, which is in accordance with band structure calculations. Sensor properties were investigated using resistance measurements upon test gas exposures. The experiments were performed at fixed operating temperatures as well as on temperature modulated sensors. The films of WO3 showed excellent sensitivity to H2S gas and selectivity to other gases. The responses of temperature modulated sensors were further analyzed using mathematical transformations and pattern recognition methods whereby different gases could be distinguished. We also present a sensing technique using conduction noise as a tool for detection of alcohol vapor. The relative change of the noise, due to the inserted alcohol, can be as large as two orders of magnitude.

Self-assembly has emerged as a promising technique for fabrication of novel hybrid materials and nanostructures. The work presented in this thesis has been focused on developing nanoscale materials based on synthetic de novo designed polypeptides. The polypeptides have been utilized for the assembly of gold nanoparticles, fibrous nanostructures, and for sensing applications. The 42-residue polypeptides are designed to fold into helix-loop-helix motifs and dimerize to form four-helix bundles. Folding is primarily driven by the formation of a hydrophobic core made up by the hydrophobic faces of the amphiphilic helices. The peptides have either a negative or positive net charge at neutral pH, depending on the relative abundance of Glu and Lys. Charge repulsion thus prevents homodimerization at pH 7 while promoting hetero-dimerization through the formation of stabilising salt bridges. A Cys incorporated in position 22, located in the loop region, allowed for directed, thiol-dependent, immobilization on planar gold surfaces and gold nanoparticles. The negatively charged (Glu-rich) peptide formed homodimers and folded in solution at pH &lt; 6 or in the presence of certain metal ions, such as Zn2+. The folding properties of this peptide were retained when immobilized directly on gold, which enabled reversible assembly of gold nanoparticles resulting in aggregates with well-defined interparticle separations. Particle aggregation was found to induce folding of the immobilized peptides but folding could also be utilized to induce aggregation of the particles by exploiting the highly specific interactions involved in both homodimerization and hetero-association. The possibility to control the assembly of polypeptide-functionalized gold nanoparticles was utilized in a colorimetric protein assay. Analyte binding to immobilized ligands prevented the formation of dense particle aggregates when subjecting the particles to conditions normally causing extensive aggregation. Analyte binding could hence easily be distinguished by the naked eye. Moreover, the peptides were utilized to assemble gold nanoparticles on planar gold and silica substrates. Fibrous nanostructures were realized by linking monomers through a disulphide-bridge. The disulphide-linked peptides were found to spontaneously assemble into long and extremely thin peptide fibres as a result of a propagating association mediated by folding into four-helix bundles. / Ingenjörer och vetenskapsmän har ofta inspirerats av naturen i sökandet efter lösningar på tekniska problem. Allt ifrån byggnadskonstruktioner, flygplansvingar, kompositmaterial till kardborrebandet har skapats med utgångspunkt från förebilder i naturen. Många av de material och konstruktioner som återfinns i naturen har åtråvärda egenskaper som är svåra att erhålla i syntetiska matrial med traditionell teknik. Även om vi i flera fall kan härma sammansättningen och formen blir resultatet inte nödvändigtvis det samma. Den största skillnaden mellan syntetiska material och material producerade av levande organismer är hur deras komponenter sinsemellan är organiserade och sammansatta. I syntetiska material är komponenterna ofta inbördes mer eller mindre slumpvis ordnade medan de i biologiska material är organiserade med en oerhörd precision som sträcker sig ända ned på molekyl- och atomnivå. Naturens byggstenar har genom evolutionens gång förfinats för att spontant kunna organisera sig och bilda komplexa material  och strukturer. Denna process, som styrs genom att många svaga krafter inom och mellan byggstenarna samverkar, kallas ofta för självorganisering och är en förutsättning för allt liv. Självorganisering har också blivit en allt viktigare metod inom nanotekniken för att konstruera material och strukturer med nanometerprecision. I den här avhandlingen beskrivs en typ av självorganiserande material där byggstenarna utgörs av nanometerstora guldpartiklar och syntetiska proteiner. De syntetiska proteinerna är designade för att efterlikna naturliga biomolekyler och antar en välbestämd tredimensionell struktur när två av dem interagerar med varandra. Denna interaktion är mycket specifik men kan styras genom att variera kemiska parametrar som surhet och jonstyrka vilket ger en möjlighet att påverka och kontrollera proteinernas struktur. Proteinerna har vidare modifierats för att spontant organisera sig till fibrer som är flera mikrometer långa men endast några nanometer tjocka. Proteinfibrer utgör en mycket viktig typ av strukturer i biologiska system och finns i alltifrån spindelväv till muskler. Syntetiska proteinfibrer är därför både ett intressant modellsystem och ett material med många potentiellt intressanta användningsområden. Genom att fästa de syntetiska proteinerna på ytan av guldnanopartiklar går interaktionerna mellan partiklarna att kontrollera på samma sätt som interaktionerna mellan proteinerna. Krafterna mellan proteinerna och interaktionerna involverade i proteinernas veckning har använts för att reversibelt aggregera och organisera nanopartiklarna. Ett antal olika byggstenar har studerats och utvecklats till något som liknar ett mycket enkelt nano-Lego, som på en given signal spontant bygger ihop sig eller trillar isär. Guldnanopartiklar är intressanta eftersom de är stabila och lätta att modifiera kemiskt men också på grund av deras optiska egenskaper som ger dem en ovanligt vacker vinröd färg. Färgen uppstår på grund av partiklarnas ringa storlek och varierar naturligt med egenskaperna hos den omgivande miljön. Detta gör det enkelt att studera hur partiklarna interagerar eftersom de byter färg när de närmar sig varandra, men gör dem också intressanta för sensortillämpningar. En enkel och robust sensor beskrivs i avhandlingen där syntetiska proteiner, speciellt utformade för att upptäcka och binda andra molekyler, har fästs på nanopartiklarna. Med partiklarnas hjälp går det att med blotta ögat detektera ett mänskligt protein i koncentrationer under ett tusendels gram per liter. En tidig diagnos av sjukdomstillstånd kan i de flesta fall avsevärt underlätta behandlingen och behovet av enkla sensorer för att bestämma närvaro och koncentration av medicinskt intressanta molekyler är därför mycket stort.

A real-time, mobile Scanning Electrical Mobility Spectrometer (SEMS) was designed using a Condensation Particle Counter (CPC) and Differential Mobility Analyzer (DMA) to measure the size distribution of nanoparticles. The SEMS was calibrated using monodisperse Polystyrene Latex (PSL) particles, and was then applied to study the size distribution of TiO2 nanoparticle aerosols generated by spray drying water suspensions of the nanoparticles. The nanoparticle aerosol size distribution, the effect of surfactant, and the effect of residual solvent droplets were determined. The SEMS system was designed by integrating the Electrical System, the Fluid Flow System, and the SEMS Software. It was calibrated using aerosolized Polystyrene Latex (PSL) spheres with nominal diameters of 99 nm and 204 nm. TiO2 nanoparticle aerosols were generated by atomizing water suspensions of TiO2 nanoparticles using a Collison nebulizer. Size distribution of the TiO2 aerosol was measured by the SEMS, as well as by TEM. Furthermore, the effect of surfactant, Tween 20 at four different concentrations between 0.01mM and 0.80mM, and stability of aerosol concentration with time were studied. It was hypothesized that residual particles in DI water observed during the calibration process were a mixture of impurities in water and unevaporated droplets. Solid impurities were captured on TEM grids using a point-to-plane Electrostatic Precipitator (ESP) and analyzed by Energy Dispersive Spectroscopy (EDS) while the contribution of unevaporated liquid droplets to residual particles was confirmed by size distribution measurements of aerosolized DI water in different humidity conditions. The calibration indicated that the mode diameter was found to be at 92.5nm by TEM and 95.8nm by the SEMS for 99nm nominal diameter particles, a difference of 3.6%. Similarly, the mode diameter for 204nm nominal diameter particles was found to be 194.9nm by TEM and 191nm by SEMS, a difference of 2.0%. Measurements by SEMS for TiO2 aerosol generated by Collison nebulizer indicated the mode diameters of 3mM, 6mM, and 9mM concentrations of TiO2 suspension to be 197.5nm, 200.0nm and 195.2nm respectively. On the other hand, the mode diameter was found to be approximately 95nm from TEM analysis of TiO2 powder. Additionally, concentration of particles generated decreased with time. Dynamic Light Scattering (DLS) measurements indicated agglomeration of particles in the suspension. Furthermore, the emulation of single particle distribution was not possible even after using Tween 20 in concentrations between 0.01mM and 0.80mM. From the study of residual particles in DI water, it was found that residual particles observed during the aerosolization of suspensions of DI water were composed of impurities present in DI water and unevaporated droplets of DI water. Although it was possible to observe solid residual particles on the TEM grid, EDS was not able to determine the chemical composition of these particles.

<p>Methylmercury is a bioaccumulative neurotoxin that severely endangers human health. Humans are exposed to methylmercury through consumption of contaminated aquatic fish. To date, effective strategies for preventing and remediating methylmercury contamination have remained elusive, mainly due to the lack of knowledge in regard to how methylmercury is generated and degraded in the aquatic environment. The goal of this dissertation was to study the mechanisms of two transformation processes that govern the fate of methylmercury in natural settings: microbial mercury methylation and methylmercury photodegradation. The role of mercury speciation (influenced by environmental conditions) in determining the reactivity of mercury in these biological and photochemical reactions was the focus of this research.</p><p>Methylmercury production in the aquatic environment is primarily mediated by anaerobic bacteria in surface sediments, particularly sulfate reducing bacteria (SRB). The efficiency of this process is dependent on the activity of the methylating bacteria and the availability of inorganic divalent mercury (Hg(II)). In sediment pore waters, Hg(II) associates with sulfides and dissolved organic matter (DOM) to form a continuum of chemical species that include dissolved molecules, polynuclear clusters, amorphous nanoparticles and after long term aging, bulk-scale crystalline particles. The methylation potential of these mercury species were examined using both pure cultures of SRB and sediment slurry microcosms. The results of these experiments indicated that the activity of SRB was largely determined by the supply of sulfate and labile carbon, which significantly influenced the net methylmercury production in sediment slurries. The availability of mercury for methylation decreased during aging. Dissolved Hg-sulfide (added as Hg(NO3)2 and Na2S) resulted in the highest methylmercury production. Although the methylation potential of humic-coated HgS nanoparticles decreased with an increase in the age of nanoparticle stock solutions, nano-HgS was substantially more available for microbial methylation relative to microparticulate HgS, possibly due to the smaller size, larger specific surface area and more disordered structure of the nanoparticles. Moreover, the methylation of mercury derived from nanoparticles cannot be explained by equilibrium speciation of mercury in the aqueous phase (<0.2 <em>f</em>Ým, the currently-accepted approach for assessing mercury bioavailability for methylation). Instead, the methylation potential of mercury sulfides appeared to correlate with the extent of dissolution and their reactivity in thiol ligand exchange. Additionally, partitioning of mercury to a diverse group of bulk-scale mineral particles and colloids (especially FeS) may be an important process controlling the mercury speciation and subsequent methylmercury production in natural sediments.</p><p>In surface waters, sunlight degradation is believed to be the predominant pathway for the decomposition of methylmercury. The mechanism of this process was investigated in a series of photodegradation experiments under natural sunlight and UV-A radiation, and in the presence of DOM and selective quenchers for photo-generated reactive intermediates. The results suggested that singlet oxygen generated from photosensitization of DOM drove the photodecomposition of methylmercury. The rate of methylmercury degradation depended on the type of methylmercury (CH3Hg+) binding ligand present in the water. CH3Hg -thiol (e.g., glutathione, mercaptoacetate, DOM) complexes were significantly more reactive in photodegradation compared to other methylmercury complexes (CH3HgCl or CH3HgOH), which may be because thiol-binding can effectively decrease the activation energy and thus enhance the reactivity of methylmercury molecules toward the Hg-C bond breaking process. These findings challenge the long-accepted view that water chemistry characteristics do not affect the kinetics of methylmercury sunlight degradation, and help explain recent field observation that methylmercury photodegradation occurred rapidly in freshwater lakes (where CH3Hg-DOM dominate methylmercury speciation) but relatively slowly in sea water (where CH3Hg-Cl control methylmercury speciation).</p><p>Overall, this dissertation has demonstrated that chemical speciation of inorganic mercury and methylmercury determines their availability for microbial methylation and sunlight degradation, respectively. The abundance of these available mercury species is influenced by a variety of environmental parameters (e.g., DOM). This dissertation work contributes mechanistic knowledge toward understanding the occurrence of methylmercury in the aquatic environment. This information will ultimately help construct quantitative models for accurately predicting and assessing the risks of mercury contamination.</p> / Dissertation

The feasibility of highly dispersed gold nanocatalyst supported on yttria-stabilized zirconia (YSZ) for the model reactions of C2H4 and CO oxidation is demonstrated for the first time. Gold nanoparticles are synthesized on YSZ powder by chemical reduction of the precursor salt in the mixture of ethanol, water and polyvinylpyrrolidone (PVP). Resulting metal loading of the catalysts are 1 wt.% with average particle sizes ranging from 6 to 9 nm. Results of CO and C2H4 oxidation display catalytic activity at 65 0C and 25 0C for CO and C2H4 oxidation, respectively. The catalytic properties of the catalysts are different due to their average particle size. Electrochemical Promotion of Catalysis (EPOC) of C2H4 oxidation is demonstrated. Application of constant potential difference between two electrodes in the bipolar electrochemical cell led to increase in C2H4 conversion. A proposed mechanism explains the bipolar EPOC phenomenon through formation of O2- flux across the electrochemical cell, resulting in the change of Work Function of gold nanoparticles placed in between the electrodes and is electronically isolated.