Fungos filamentosos com capacidade de produzir micotoxinas podem estar presentes em alimentos, desde o cultivo até o produto após industrialização. Devido a isso, estratégias para controlar o crescimento fúngico devem ser investigadas, a fim de evitar o desenvolvimento desses microrganismos, bem como a produção de suas toxinas nos alimentos. Neste trabalho, duas abordagens para o controle de fungos toxigênicos foram avaliadas. A primeira estratégia foi a utilização de bactérias provenientes de diferentes ambientes aquáticos, sendo que 10 linhagens de Bacillus spp. e a linhagem Pseudomonas sp. 4B foram testadas quanto à influência sobre os parâmetros de crescimento (taxas de crescimento micelial, esporulação e germinação de esporos) de fungos toxigênicos (Aspergillus e Penicillium) e formação de micotoxinas. Todas as bactérias foram capazes de inibir o crescimento dos fungos em meio de cultura, apresentando halos de inibição variando de 1,0 até 15,7 mm. Bacillus sp. P11 apresentou resultados mais expressivos em relação às demais linhagens do gênero Bacillus com maiores valores de redução na maioria dos parâmetros de crescimento. Além disso, Bacillus sp. P11 e Pseudomonas sp. 4B apresentaram efeito sobre as taxas de crescimento micelial, esporulação e germinação de esporos, com níveis de redução acima de 43,3, 32,1 e 84,1% respectivamente. Mesmo assim, as demais linhagens também apresentaram resultados satisfatórios sobre esses parâmetros. Estas bactérias também reduziram a síntese de aflatoxina B1 e ocratoxina A em mais de 94 e 63%, respectivamente, quando cultivadas simultaneamente com os fungos produtores de cada micotoxina. Adicionalmente, a capacidade de Bacillus sp. P11 em produzir os lipopeptídeos iturina A (167,9 mg/mL de extrato butanólico) e surfactina (361,9 mg/mL de extrato butanólico) foi confirmada. Estes compostos podem ter contribuído para a atividade antifúngica desta bactéria. A segunda estratégia investigada neste estudo para controlar o desenvolvimento de fungos toxigênicos foi o emprego de nanofibras de poli-ɛ-caprolactona (PCL) incorporadas com cetoconazol e natamicina como material antimicrobiano. Nesta abordagem, as nanofibras foram produzidas pela técnica de eletrofiação e posteriormente caracterizadas e avaliadas quanto ao seu potencial antifúngico. Nanofibras funcionalizadas com cetoconazol ou natamicina apresentaram atividade antifúngica contra os isolados toxigênicos uma vez que zonas de inibição variando de 6 a 44 mm foram observadas. Além disso, as análises de microscopia eletrônica e espectroscopia demonstraram que a incorporação dos antifúngicos não altera de forma expressiva as principais características das nanofibras. Também foi possível verificar a capacidade de liberação controlada dos antifúngicos durante 72 h de contato das nanofibras com diferentes soluções simulantes. Valores próximos a 80 e 45 μg/mL de cetoconazol e natamicina, respectivamente, foram observados em solução de Tween 20 (5%). Portanto, o processo de eletrofiação foi capaz de agregar propriedades antifúngicas às nanofibras de PCL. Os resultados demonstraram que as bactérias e os nanomateriais investigados neste estudo são promissores para o controle de fungos toxigênicos e produção de micotoxinas. / Filamentous fungi that have the potential to produce mycotoxins may be present in food, from cultivation to after industrialization. Therefore, several strategies to control fungal growth must be investigated in order to avoid the development of these microorganisms and the production of their toxins in food. In this work, two approaches to toxigenic fungi control were evaluated. The first one was the use of bacteria from different aquatic environments as biocontrol agents in which 10 Bacillus spp. strains and the Pseudomonas sp. 4B strain were tested in relation to the effect on growth parameters (mycelial growth, sporulation and spore germination rates) of toxigenic fungi (Aspergillus and Penicillium) and mycotoxin formation. All bacteria were able to inhibit the fungal growth in culture medium with inhibition zones ranging from 1.0 to 15.7 mm. It was also observed that Bacillus sp. P11 had better results compared to other Bacillus strains with larger reduction values in most of growth parameters. Furthermore, Bacillus sp. P11 and Pseudomonas sp. 4B exhibited effect on mycelial growth, sporulation and spore germination rates with reduction values above of 43.3, 32.1 and 84.1%, respectively. Even so, the other strains also showed satisfactory results on these parameters. Finally, these bacteria reduced the synthesis of aflatoxin B1 and ochratoxin A at levels above 94 and 63%, respectively, when co-cultivated with each mycotoxin producing fungi. Additionally, the ability of Bacillus sp. P11 to produce lipopeptides such as iturin A (167.9 mg/ml of butanolic extract) and surfactin (361.9 mg/ml of butanolic extract) was confirmed. These compounds may have contributed to antifungal activity of this bacterium. The second investigation of this work in order to control the growth of toxigenic fungi was the use of poly-ε-caprolactone nanofibers incorporated with ketoconazole and natamycin as antimicrobial material. In this approach, nanofibers were produced by the electrospinning technique and subsequently characterized and evaluated for their antifungal potential. Both nanofibers functionalized with ketoconazole and natamycin showed antifungal activity against toxigenic isolates since inhibitory zones ranging from 6 to 44 mm were observed. In addition, scanning electron microscopy and infrared spectroscopy analysis showed that the antifungals incorporation does not change the characteristics of nanofibers. It was also possible to verify the ability of controlled drug release during 72 h of nanofibers contact with different simulants solutions. Values near 80 and 45 μg/ml of ketoconazole and natamycin, respectively, were observed in the solution containing 5% Tween 20. Therefore, the electrospinning process was able to provide antifungal properties to the nanofibers. The results showed that bacteria and nanomaterials investigated in this study are promising for developing control strategies of toxigenic fungi and mycotoxin production.

No description available.

Graphene and other two-dimensional materials can be stacked together to form vander Waals heterostructures: synthetic crystals composed of different atomically thin layers with a bespoke electronic band structure. Structural characterisation of vander Waals heterostructures is difficult using conventional methods as the properties are almost entirely defined by the nature of the buried interfaces between dissimilar crystals. These methods also fall short of resolving the atomic structure of buried defects in van der Waals materials such as graphite. This work demonstrates the refinement and successful application of ion beam specimen preparation to produce cross sectional slices through these unique crystals so that they can be characterised by high resolution scanning transmission electron microscopy (STEM). Cross sectional specimen were prepared using in situ lift-out in a focused ion beam (FIB) dual-beam instrument. The fine polishing steps were optimised to prevent damage to the core of the specimen. High resolution STEM imaging of twin defects in graphene, hexagonal boron ni-tride and MoSe2 revealed that the boundaries are not atomically sharp but extended across many atoms. Advanced processing and analysis of these images uncovered fundamental mechanics which govern their geometry. This technique was further applied to complex transition metal dichalcogenide heterostructures to quantitatively determine the properties of buried interfaces between atomically thin crystals.

Cette thèse présente l’étude de nanocristaux semi-conducteurs pour leur intégration dans des dispositifs de conversion thermoélectrique. Ce phénomène permet de générer un courant à partir d’une différence de température entre deux faces, reliées par deux pieds conducteurs de charges. Les matériaux les plus efficaces à température ambiante sont basés sur le tellurure de bismuth Bi2Te3, qui est toxique et coûteux. Une étude théorique et bibliographique, portant sur les grandeurs caractéristiques de la conversion thermoélectrique, est réalisée. Elle permet de déterminer les matériaux d’intérêt en fonction de leur coût et de leur efficacité, que l’on peut optimiser à travers différents paramètres d’influence. La chalcopyrite, CuFeS2, présente des propriétés intéressantes en thermoélectricité, et offre une alternative intéressante aux matériaux classiques, car composée d’éléments abondants et non-toxiques. La synthèse par voie chimique choisie permet de contrôler la composition du matériau, et d’obtenir des nanocristaux de taille contrôlée entre 30 et 50 nm, pour diffuser les phonons dans le matériau et diminuer sa conductivité thermique. La thèse s’oriente autour de l’étude de ces nanocristaux semi-conducteurs de CuFeS2, organisée en deux parties principales.La première partie décrit la synthèse par voie chimique des nanocristaux et leur étude structurale. Deux méthodes de synthèse sont optimisées et permettent de contrôler finement la stœchiométrie du matériau, et d’accéder à des cristaux de différentes tailles et morphologies. Une étude complète de la composition des nanocristaux est réalisée par XPS, EDX et thermogravimétrie. L’étude du matériau par diffraction des rayons X met en évidence l’influence de la composition chimique des nanocristaux, et des conditions de température et de pression sur la phase cristalline du matériau. Une transition de phase de la wurtzite vers la chalcopyrite est décrite.Dans la seconde partie sont étudiées les propriétés thermoélectriques des nanocristaux synthétisés. Leur mise en forme en pieds thermoélectriques monolithiques est décrite, ainsi que l’optimisation de leurs propriétés thermoélectriques à travers trois stratégies. Le matériau obtenu est un conducteur de type n, qui permet la conduction des électrons. Sa conductivité thermique est réduite par nanostructuration. La première stratégie consiste à faire varier la composition des nanocristaux, et plus particulièrement le rapport entre charges cationiques et anioniques, pour modifier le taux de dopage du matériau, et ainsi modifier sa conductivité électrique et son coefficient Seebeck. La seconde voie d’amélioration consiste à remplacer les ligands isolants présents après la synthèse des nanocristaux par des ligands courts et conducteurs, pour augmenter la conductivité électrique du matériau. Enfin, des nanoparticules métalliques d’argent, d’étain et de cuivre sont introduites en mélange avec les nanocristaux afin d’augmenter la conductivité électrique du matériau nanocomposite ainsi créé.Cette thèse apporte des éléments de compréhension entre la structure et la composition de matériaux ternaires et leurs propriétés thermoélectriques, et permet d’envisager une amélioration de leurs performances. Les matériaux optimisés présentent des efficacités comparables aux résultats de la littérature pour cette famille de matériaux, notamment autour de la température ambiante. A travers une combinaison efficace des facteurs d’influence étudiés, ces efficacités pourront être dépassées lors de futurs travaux, et le matériau intégré à un dispositif de conversion thermoélectrique couplé à une cellule photovoltaïque, pour la conversion de l’énergie solaire par les deux phénomènes. / This thesis presents the studies made on semiconducting nanocrystals, to be integrated in thermoelectric generators. Thermoelectricity generates a current through a temperature difference between two faces, connected by thermoelectric legs which conduct the charges. Nowadays, the most efficient materials at room temperature contains tellurium, which is toxic and expansive due to its scarcity. A study on theory and literature is carried to understand the underlying phenomena which help us explain the thermoelectric conversion. The potentially interesting materials are selected for their cost and efficiency, tunable by varying different parameters. Chalcopyrite, of formula CuFeS2, presents promising properties for thermoelectricity, and offers an interesting way to replace classic materials as a non-toxic earth-abundant substitute. The chemical synthesis allows to control the composition of the material and to obtain 30 to 50 nm sized nanocrystals, able to scatter phonons and diminish the thermal conductivity of the material as a consequence. The thesis is describing the study of these semiconducting CuFeS2 nanocrystals, and is divided in two main parts.The first part describes the chemical synthesis of the nanocrystals and the characterization of their structure. Two ways of synthesis are developed and optimized, allowing to control the stoichiometry of the material, and to obtain crystals of different sizes and shapes. A complete study of the composition of the nanocrystals is made by XPS, EDX and thermogravimetric analysis. The study of the material by X-ray diffraction shows that the chemical composition of the nanocrystals, as well as the temperature and the pressure, have an influence on their crystalline phase. A phase transition from the wurtzite phase to the chalcopyrite phase is described.In the second part, are studied the thermoelectric properties of the nanocrystals. Their preparation as solid materials is described. The improvement made on their efficiency is following three main paths. The obtained material is a n type conductor, which means it carries electrons. Its thermal conductivity is reduced due to the nanostructuration. The first strategy consists in varying the composition of the nanocrystals, and especially the ratio between positive and negative charges, carried by ions, to modify the electrical conductivity and Seebeck coefficient of the material through doping. The second way of improvement is by replacing the native insulating ligands of the nanocrystals by short inorganic conducting ones, to increase the electrical properties of the material. Finally, metallic nanoparticles, of silver, tin and copper, are blended with the nanocrystals to improve the electrical conductivity of the resulting nanocomposite material.This thesis helps one to understand the relation between structure, composition and thermoelectrical properties of ternary semiconducting materials. It is possible to think of ways of improvement for the studied materials. Our best results are state of the art for this family of materials, especially around room temperature. There is room for improvement, with a proper combination of the studied parameters. During a future work, the optimized material could be integrated to a thermoelectric - photovoltaic device, for conversion of the solar energy through the two phenomena.

By the year 2020, the nanotechnology market is expected to be three trillion dollars. With a quasi-exponential increase in consumer products, which contain nanomaterials, there is likely to be an equal increase in nanoparticles entering the environment. As a result, it is imperative to fully understand the relationship between nanomaterials and the food chain, including plants. In this study, the relationship between gold nanomaterials and the edible food crop, Helianthus annuus was investigated. First, an attempt to inhibit the uptake of nanoparticles into the roots of H. annuus was investigated by decreasing temperature. Second, the interactions between citrate-stabilized 20 nm diameter Au nanoparticles and sunflower seedlings were explored by exposing sunflower to a range of concentrations (3.0-40.0 mg/L). Nanoparticle sorption to roots was estimated using a linear isotherm with a distribution coefficient, Kd. Finally, sunflowers were exposed to 20 nm Au nanoparticles and 25x69 nm CTAB-stabilized Au nanorods. Results showed there was no change in biomass growth and transpiration between sunflowers that were exposed to nanoparticles and the unexposed controls. Thus Au gold nanoparticles (20 nm) were shown to have no phytostimulatory or phytotoxic effect on sunflower seedlings during eight to ten day exposure experiments. However, 25x69 nm gold nanorods were phytotoxic to sunflowers at 6.0 mg/L, indicating a potential charge or chemical effect of the surface coating of the nanorods compared to the spherical gold nanoparticles.

This dissertation focuses on the synthesis and characterization of glyconanomaterials, as well as their applications in studying carbohydrate-protein interactions. A new and versatile method for coupling underivatized carbohydrates to nanomaterials including gold and silica nanoparticles was developed via the photochemically induced coupling reaction of perfluorophenylazide (PFPA). A wide range of carbohydrates including mono-, oligo- and poly-saccharides were conjugated to the nanoparticles with high yields and efficiency. New analytical methods were developed to determine the binding affinities of glyconanoparticles (GNPs) with lectins; these include fluorescence-based competition assay, dynamic light scattering (DLS) and isothermal titration calorimetry (ITC). Results showed that the multivalent presentation of carbohydrate ligands significantly enhanced the binding affinity of GNPs by several orders of magnitude compared to the free ligands. Systematic studies were carried out to investigate the impact of ligand presentation, i.e., the type and length of spacer linkage, the ligand density and the nanoparticle size on the binding affinity of the resulting glyconanoparticles. We used gold GNPs to study interactions with anti-HIV lectin cyanovirin-N (CV-N), and dye-doped silica nanoparticles for labeling glyans and developing high-throughput screening technique.

Studying physical properties of nanoscale materials has gained a significant attention owing to their applications in the fields such as electronics, medicine, pharmaceutical industry, and materials science. However, owing to size constraints, number of techniques that measures physical properties of materials at nanoscale with a high accuracy and sensitivity is limited. In this context, development of atomic force microscopy (AFM) based techniques to measure physical properties of nanomaterials has led to significant advancements across the disciplines including chemistry, engineering, biology, material science and physics. AFM has recently been utilized in the quantification of physical-chemical properties such as electrical, mechanical, magnetic, electrochemical, binding interaction and morphology, which are enormously important in establishing structure-property relationship. The overarching objective of the investigations discussed here is to gain quantitative insights into the factors that control electrical and mechanical properties of nano-dimensional organic materials and thereby, potentially, establishing reliable structure-property relationships particularly for organic molecular solids which has not been explored enough. Such understanding is important in developing novel materials with controllable properties for molecular level device fabrication, material science applications and pharmaceutical materials with desirable mechanical stability. First, we have studied electrical properties of novel silver based organic complex in which, the directionality of coordination bonding in the context of crystal engineering has been used to achieve materials with structurally and electrically favorable arrangement of molecules for an enhanced electrical conductivity. This system have exhibited an exceptionally high conductivity compared to other silver based organic complexes available in literature. Further, an enhancement in conductivity was also observed herein, upon photodimerization and the development of such materials are important in nanoelecrtonics. Next, mechanical properties of a wide variety of nanocrystals is discussed here. In particular, an inverse correlation between the Young’s modulus and atomic/molecular polarizability has been demonstrated for members of a series of macro- and nano-dimensional organic cocrystals composed of either resorcinol (res) or 4,6-di-X-res (X = Cl, Br, I) (as the template) and trans-1,2-bis(4-pyridyl)ethylene (4,4’-bpe) where cocrystals with highly-polarizable atoms result in softer solids. Moreover, similar correlation has been observed with a series of salicylic acid based cocrystals wherein, the cocrystal former was systematically modified. In order to understand the effect of preparation method towards the mechanical properties of nanocrystalline materials, herein we have studied mechanical properties of single component and two component nanocrystals. Similar mechanical properties have been observed with crystals despite their preparation methods. Furthermore, size dependent mechanical properties of active pharmaceutical ingredient, aspirin, has also been studied here. According to results reduction in size (from millimetre to nanometer) results in crystals that are approximately four fold softer. Overall, work discussed here highlights the versatility of AFM as a reliable technique in the electrical, mechanical, and dimensional characterization of nanoscale materials with a high precision and thereby, gaining further understanding on factors that controls these processes at nanoscale.

Au cours des dernières décennies, en raison de sa stabilité́ chimique et thermique exceptionnelle associée à son caractère isolant, le nitrure de bore hexagonal sous forme de nanofeuillets (BNNSs) trouve un grand intérêt dans de nombreuses applications. En effet, il est sérieusement envisagé l’utilisation de ces nanomatériaux comme support de graphene ou pour la fabrication d’hétérostructures horizontales utilisables dans le domaine de la microélectronique pour des applications de nouvelle génération. Il existe deux grandes voies de synthèse de ces nanostructures 2D de h-BN, par dépôt chimique en phase vapeur (CVD), ou par exfoliation d’un monocristal. Dans le but de préparer des BNNS de grande qualité́ chimique et cristalline, notre groupe propose une nouvelle stratégie de synthèse en associant la voie polymère précéramique (PDC) à des techniques de frittage, par Spark Plasma Sintering (SPS) et Hot Isostatic Pressing (HIP). Premièrement, le comportement thermique du précurseur précéramique, le polyborazilène (PBN) a été étudié en conditions dynamiques in-situ. Il a ainsi été mis en évidence, le rôle bénéfique du promoteur de cristallisation (Li3N) sur la qualité cristalline du matériau final. Cependant, une étape de frittage complémentaire reste obligatoire pour parfaire la structuration cristalline du h-BN. Premièrement, un procédé́ de frittage par SPS a été mis en œuvre. Dans cette étude, ont été particulièrement étudiés l’influence de la température de frittage (1200-1950°C) ainsi que la teneur en promoteur de cristallisation (0-10% mass.) sur la qualité cristalline du matériau final. Après optimisation des conditions de synthèse, des pastilles de h-BN composées d’une grande quantité de plaquettes monocristallines de taille d’environ 200 μm2 ont été obtenues. Les caractérisations de ces monocristaux attestent d'une haute qualité́ chimique et cristalline, même si des impuretés, sans doutes dues à l’environnement en graphite dans le SPS, sont détectées par cathodoluminescence. Enfin, des mesures physiques montrent que les BNNSs préparés présentent une constante diélectrique intéressante de 3,9, associée à une résistance diélectrique correcte de 0,53 V/nm. Afin d’augmenter encore la taille des monocristaux préparés, un second procédé́ de frittage, par HIP, a été étudié́. Cette autre combinaison originale conduit alors à des monocristaux de h-BN significativement plus gros (jusqu’à 2000 μm de taille latérale), transparents, incolores et très faciles à exfolier. Ainsi cette nouvelle association de la synthèse de PBN par voie PDCs et du procédé́ de céramisation par HIP nous semble une voie des plus prometteuses pour générer de grands monocristaux de h-BN et des nanofeuillets susceptibles de supporter des hétérostructures à base de graphène. / In the past decades, due to their exceptional chemical and thermal stabilities together with their electrical insulation properties, hexagonal boron nitride nanosheets (BNNSs) have become a promising support substrate for graphene and promoted the incentive of various van der Waals heterostructures. For such applications, BNNSs are generally obtained by Chemical Vapor Deposition (CVD) or exfoliation. In order to achieve high quality and large BNNSs, our group has proposed a novel synthesis strategy based on the Polymer Derived Ceramics (PDCs) route combined with sintering techniques: Spark Plasma Sintering (SPS) or Hot Isostatic Pressing (HIP). Since hexagonal boron nitride (h-BN) crystallization is a key point in the synthesis of high quality BNNSs, efforts have been led to understand the beneficial role of a promotor of crystallization (Li3N), adopting a suitable in situ dynamic approach. It has been established that Li3N does improve the crystallization level of the product, and lower the transformation temperatures from polyborazylene to h-BN. Then, we have further investigate the influence of the SPS sintering temperature (1200-1950°C) and of the crystal promoter content (Li3N, 0-10 wt.%) on BN growth. The tested SPS parameters strongly modify the size of the resulting h-BN flakes. For an optimal Li3N concentration of 5 wt.%, h-BN flakes larger than 200 μm2 (average flake area) have been obtained. A high degree of crystallinity and purity have been achieved, even if the very-sensitive cathodoluminescence technic indicated traces of impurities, probably due to surrounding graphite parts of the SPS. Few-layered BNNSs have been successfully isolated, through exfoliation process. As a final application purpose, further physical measurements have confirmed that SPS derived h-BN exhibits an interesting dielectric constant of 3.9 associated with a dielectric strength of 0.53 V/nm. Due to a very high compact character of SPS-derivative h-BN crystals, the post-exfoliation step is made very difficult, resulting in BNNSs of tens of microns lateral size. Therefore, we have studied another sintering procedure by HIP for the ceramization process. Through this combination, we aim to promote the size of h-BN single crystals, leading to larger size exfoliated BNNSs. Characterizations from bulk crystals to BNNSs have been carried out in three aspects: morphology, lattice structure and chemical composition. This novel attempt has provided us transparent and colorless h-BN single crystals with large lateral size, up to 2000 μm. Besides, BNNSs with high purity have also been confirmed. HIP, as a new ceramization process of PDCs, has to be considered as a promising way to obtain large h-BN single crystals and nanosheets for supporting graphene and 2D heterostructures.

Methods based on the atomic force microscope (AFM) were implemented or developed to measure and map at the nanoscale the mechanical properties of polymer surfaces and of nanomaterials: force spectroscopy, force modulation, phase detection in intermittent-contact mode. Especially, a technique, referred as resonant contact-AFM, was developed. It is based on the electrostatic excitation of the cantilever vibration and on the measurement of its resonance frequency when the tip contacts the probed sample. A theoretical model was developed to determine the tip-sample contact stiffness from the measurement of the frequency shift. These methods were used to study several questions raised in the fields of polymer surfaces and interfaces and of nanomaterials. Surfaces of toughened polypropylene (PP) with ethylene-propylene copolymer (EP) were studied by force spectroscopy and force modulation microscopy (FMM) to characterise the effect of the blending and the moulding processes and the PP/EP viscosity ratio on the surface distribution of the EP rubber nodules. The contribution of the EP rubber to paint adhesion was also demonstrated. Surfaces of atactic polypropylene photo-grafted with acrylic acid monomers were analysed by intermittent-contact AFM (IC-AFM) with phase detection. The combination of these methods with other analytical techniques allowed characterising the chemical composition of the heterogeneous surface morphology obtained after photo-grafting. The tensile elastic modulus of polymer nanotubes and metallic nanowires was measured with force spectroscopy and resonant contact-AFM. These measurements confirmed the ability of resonant contact-AFM to quantitatively measure the mechanical properties of nanomaterials. Moreover, they showed that the measured modulus increased when the nanowires or nanotubes diameter decreases. This behaviour was explained by taking into account the effect of the surface deformation that added a surface stiffness proportional to the surface tension, or surface stress, of the material. Resonant contact-AFM was also used to characterise the variation of the mechanical properties at the interfaces in polymer blends. It was demonstrated that this technique allows the determination of the interfacial width in incompatible polymer blends. It also allowed characterising the mechanical property gradient that can appear in reactive polymer blends.

Successful operation of Nano-ElectroMechanical Systems (NEMS) critically depends on their working environment and component materials' electromechanical properties. It is equally important that ambient or liquid environment to be seriously considered for NEMS to work as high sensitivity sensors with commercial viabilities. Firstly, to understand interaction between NEMS oscillator and fluid, transfer function of suspended gold nanowire NEMS devices in fluid was calculated. It was found that NEMS's resonance frequency decreased and energy dissipation increased, which constrained its sensitivity. Sensitivity limit of NEMS oscillators was also considered in a statistical framework. Subsequently, suspended gold nanowire NEMS devices were magnetomotively actuated in vacuum and liquid. Secondly, electromechanical properties of gold nanowires were carefully studied and the observed size effect was found to agree with theory, which predicted small changes of electromechanical property compared with bulk gold materials. Finally, it is well recognized that continuous development of new NEMS devices demands novel materials. Mechanical properties of new two-dimensional hexagonal Boron Nitride films with a few atomic layers were studied. Outlook of utilizing ultrathm BN films in next generation NEMS devices was discussed.