Nano-grids of Yeast Cytochrome C

One innovative thought in biomolecular electronics is the exploitation of electron transfer proteins. Using nature's self assembly techniques, proteins can build highly organized edifices with retained functional activity, and they can serve as platforms for biosensors. In this research work, Yeast Cytochrome C (YCC) is immobilized with a help of a linker molecule, 3-Mercaptopropyltrimethoxysilane (3-MPTS) on a hydroxylated surface of a silicon substrate. Atomic Force Microscopy (AFM) is used for characterization. AFM data shows immobilization of one YCC molecule in between eight grids that are formed by the linker molecules. 3-MPTS monolayers are organized in grids that are 1.2 nm apart. Immobilization of 3-MPTS was optimized using a concentration of 5 mM in a completely dehydrated state for 30 minutes. The functionally active grids of YCC can now be incorporated with Cytochrome C oxidase on a Platinum electrode surface for transfer of electrons in development of biosensors, such as nitrate sensor, that are small in size, cheaper, and easier to manufacture than the top-down approach of fabrication of molecular biodevices

An investigation by AFM and TEM of the mechanism of anodic formation of nanoporosity in n-InP in KOH

The early stages of nanoporous layer formation, under anodic conditions in the absence of light, were investigated for n-type InP with a carrier concentration of ∼3× 1018 cm-3 in 5 mol dm-3 KOH and a mechanism for the process is proposed. At potentials less than ∼0.35 V, spectroscopic ellipsometry and transmission electron microscopy (TEM) showed a thin oxide film on the surface. Atomic force microscopy (AFM) of electrode surfaces showed no pitting below ∼0.35 V but clearly showed etch pit formation in the range 0.4-0.53 V. The density of surface pits increased with time in both linear potential sweep and constant potential reaching a constant value at a time corresponding approximately to the current peak in linear sweep voltammograms and current-time curves at constant potential. TEM clearly showed individual nanoporous domains separated from the surface by a dense ∼40 nm InP layer. It is concluded that each domain develops as a result of directionally preferential pore propagation from an individual surface pit which forms a channel through this near-surface layer. As they grow larger, domains meet, and the merging of multiple domains eventually leads to a continuous nanoporous sub-surface region.

Electrochemical pore formation on InP in alkaline solutions

The surface properties of InP electrodes were examined following anodization in (NH4)2S and KOH electrolytes. In both solutions, the observation of current peaks in the cyclic voltammetric curves was attributed to selective etching of the substrate and a film formation process. AFM images of samples anodized in the sulfide solution, revealed surface pitting and TEM micrographs revealed the porous nature of the film formed on top of the pitted substrate. After anodization in the KOH electrolyte, TEM images revealed that a porous layer extending 500 nm into the substrate had been formed. Analysis of the composition of the anodic products indicates the presence of In2S3 in films grown in (NH4)2S and an In2O3 phase within the porous network formed in KOH.

Dynamically mechanical and nano-impact (fatigue) analysis of touch screen thin films deposited on polyethylene terephthalate substrate

Nano-scale touch screen thin film have not been thoroughly investigated in terms of dynamic impact analysis under various strain rates. This research is focused on two different thin films, Zinc Oxide (ZnO) film and Indium Tin Oxide (ITO) film, deposited on Polyethylene Terephthalate (PET) substrate for the standard touch screen panels. Dynamic Mechanical Analysis (DMA) was performed on the ZnO film coated PET substrates. Nano-impact (fatigue) testing was performed on ITO film coated PET substrates. Other analysis includes hardness and the elastic modulus measurements, atomic force microscopy (AFM), Fourier Transform Infrared Spectroscopy (FTIR) and the Scanning Electron Microscopy (SEM) of the film surface.
Ten delta of DMA is described as the ratio of loss modulus (viscous properties) and storage modulus (elastic properties) of the material and its peak against time identifies the glass transition temperature (Tg). Thus, in essence the Tg recognizes changes from glassy to rubber state of the material and for our sample ZnO film, Tg was found as 388.3 K. The DMA results also showed that the Ten delta curve for Tg increases monotonically in the viscoelastic state (before Tg) and decreases sharply in the rubber state (after Tg) until recrystallization of ZnO takes place. This led to an interpretation that enhanced ductility can be achieved by negating the strength of the material.
For the nano-impact testing using the ITO coated PET, the damage started with the crack initiation and propagation. The interpretation of the nano-impact results depended on the characteristics of the loading history. Under the nano-impact loading, the surface structure of ITO film suffered from several forms of failure damages that range from deformation to catastrophic failures. It is concluded that in such type of application, the films should have low residual stress to prevent deformation, good adhesive strength, durable and good resistance to wear.

Analysis of Ultrasonic Techniques for the Characterization of Microfiltration Polymeric Membranes

The use of polymeric membranes is extremely important in several industries such as nuclear, biotechnology, chemical and pharmaceutical. In the nuclear area, for instance, systems based on membrane separation technologies are currently being used in the treatment of radioactive liquid effluent, and new technologies using membranes are being developed at a great rate. The knowledge of the physical characteristics of these membranes, such as, pore size and the pore size distribution, is very important to the membranes separation processes. Only after these characteristics are known is it possible to determine the type and to choose a particular membrane for a specific application. In this work, two ultrasonic non destructive techniques were used to determine the porosity of membranes: pulse echo and transmission. A 25 MHz immersion transducer was used. Ultrasonic signals were acquired, for both techniques, after the ultrasonic waves passed through a microfiltration polymeric membrane of pore size of 0.45 μm and thickness of 180 μm. After the emitted ultrasonic signal crossed the membrane, the received signal brought several information on the influence of the membrane porosity in the standard signal of the ultrasonic wave. The ultrasonic signals were acquired in the time domain and changed to the frequency domain by application of the Fourier Fast Transform (FFT), thus generating the material frequency spectrum. For the pulse echo technique, the ultrasonic spectrum frequency changed after the ultrasonic wave crossed the membrane. With the transmission technique there was only a displacement of the ultrasonic signal at the time domain.

Exciton-mediated photothermal cooling in GaAs membranes

Cooling of the mechanical motion of a GaAs nano-membrane using the photothermal effect mediated by excitons was recently demonstrated by some of the authors (Usami et al 2012 Nature Phys. 8 168) and provides a clear example of the use of thermal forces to cool down mechanical motion. Here, we report on a single-free-parameter theoretical model to explain the results of this experiment which matches the experimental data remarkably well.

Nanofiltration membranes modified with aromatic polyamide dendrimers active layers

This thesis describes the modification of the commercial TFC-S nanofiltration membrane with shape-persistent dendritic architectures. Amphiphilic aromatic polyamide dendrimers (G1-G3) are synthesized via a divergent approach and used for membrane modification by direct percolation. The permeate samples collected from the percolation experiments are analyzed by UV-Vis spectroscopy to instantly monitor the influence of dendrimer generations on percolation behaviors and new active layer formation. The membrane structures are further characterized by Rutherford backscattering spectrometry (RBS) and atomic force microscopy (AFM) techniques, suggesting a low-level accumulation of dendrimers inside the TFC-S NF membranes and subsequent formation of an additional aramide dendrimer active layer. Thus, all the modified TFC-S membranes have a double active layer structure. A PES-PVA film is used as a control membrane showing that structural compatibility between the dendrimer and supports plays an important role in the membrane modification process. The performance of modified TFC-S membrane is evaluated on the basis of rejection abilities of a variety of water contaminants having a range of sizes and chemistry. As the water flux is inversely proportional to the thickness of the active layer, we optimize the amount of dendrimers deposited for specific contaminants to improve the solute rejection while maintaining high water flux.

Efeito do tratamento por plasma na proliferação de fibroblastos e esterilização de membranas de quitosana

Chitosan is being studied for use as dressing due their biological properties. Aiming to expand the use in biomedical applications, chitosan membranes were modified by plasma using the following gases: nitrogen (N2), methane (CH4), argon (Ar), oxygen (O2) and hydrogen (H2). The samples were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle, surface energy and water absorption test. Biological Tests were also performed, such as: test sterilization and proliferation of fibroblasts (3T3 line). Through SEM we observed morphological changes occurring during the plasma treatment, the formation of micro and nano-sized valleys. MFA was used to analyze different roughness parameters (Ra, Rp, Rz) and surface topography. It was found that the treated samples had an increase in surface roughness and sharp peaks. Methane plasma treatment decreased the hydrophilicity of the membranes and also the rate of water absorption, while the other treatments turned the membranes hydrophilic. The sterilization was effective in all treatment times with the following gases: Ar, N2 and H2. With respect to proliferation, all treatments showed an improvement in cell proliferation increased in a range 150% to 250% compared to untreated membrane. The highlights were the treatments with Ar 60 min, O2 60 min, CH4 15 min. Observing the results of the analyzes performed in this study, it appears that there is no single parameter that influences cell proliferation, but rather a set of ideal conditions that favor cell proliferation

Role of the Tryptophan Residues in the Specific interaction of the Sea Anemone Stichodacty la helianthus’s Actinoporin Sticholysin II with Biological Membranes

Actinoporins are pore-forming toxins from sea anemones. Upon interaction with sphingomyelin-containing bilayers, they become integral oligomeric membrane structures that form a pore. Sticholysin II from Stichodactyla helianthus contains five tryptophans located at strategic positions; its role has now been studied using different mutants. Results show that W43 and W115 play a eterminant role in maintaining the high thermostability of the protein, while W146 provides specific interactions for protomer−protomer assembly. W110 and W114 sustain the hydrophobic effect, which is one of the major driving forces for membrane binding in the presence of Chol. However, in its absence, additional interactions with sphingomyelin are required. These conclusions were confirmed with two sphingomyelin analogues, one of which had impaired hydrogen bonding properties. The results obtained support actinoporins’ Trp residues playing a major role in membrane recognition and binding, but their residues have an only minor influence on the diffusion and oligomerization steps needed to assemble a functional pore.

Synthesis, Modification and Characterization of Polymeric Membranes for CO2 Separation

This doctorate focused on the development of dense polymeric membranes for carbon capture, mostly in post combustion applications, and for natural gas sweetening. The work was supported by the European Project NANOMEMC2 funded under H2020 program. Different materials have been investigated, that rely on two main transport mechanisms: the solution-diffusion and the facilitated transport. In both cases, proper nano-fillers have been added to the matrix, in order to boost the mechanical and permselective properties of the membranes. Facilitated transport membranes were based on the use of was polyvinylamine (PVAm), as main matrix with fixed-site carriers, and L-Arginine as mobile carrier; the filler, used mostly as reinforcer, was carboxymethylated nanocellulose (cNFC). Humid test showed interesting results, and especially the blend made of PVAm/cNFC/Arg in weight ratio 27,5/27,5/45 crossed the Robeson CO2/N2 upper bound, representing current state of the art membranes, with a CO2 permeability of 271 Barrer and CO2/N2 selectivity of 70. Solution diffusion membranes were based on Pebax®2533 matrix which was added with three different graphene oxide (GO)-based materials, namely pristine GO, Porous Graphene Oxide (PGO) and a GO functionalized with polyetheramine (PEAGO). All of them provided a modest but clear increment of permeability of the Pebax matrix, from plus 2% (GO) to plus 8% (PGO), with no change in selectivity. The gas tested with this type of composites were CO2 and N2, for Post combustion capture applications. Pebax®2533 was also chemically modified, obtaining the product called “Benzoyl-P2533”, that was fully characterized, and tested in term of permeation using five gas: CO2, N2, CH4, O2, and He. Modified material showed an increment of the overall permeability of the material of a fair 10% for all gases tested, apart from helium, that increased of almost 50%.

Caratterizzazione di bioelettrodi elastici a polimero semiconduttore nano-strutturato

Nell'ambito della medicina bioelettronica vi è un grande interesse nello sviluppo di bioelettrodi elastici ad interfaccia nanostrutturata per la rilevazione dei segnali elettrici del sistema nervoso. Uno dei materiali organici più performanti è il polimero conduttivo 3,4-polietilenediossitiofene (PEDOT), drogato col polianione polistirene sulfonato (PSS) a formare il PEDOT:PSS nanocomposito. Questo composto tende però a perdere le proprietà elettrochimiche di partenza quando sottoposto a stress meccanico. Per ottenere una caratterizzazione del materiale è stata esaminata la spettroscopia di impedenza elettrochimica (EIS) come funzione della frequenza temporale di alcuni elettrodi d' oro rivestiti di PEDOT:PSS elettrodepositato, utilizzando dei substrati microfabbricati. Sono stati inoltre eseguiti confronti con bioelettrodi PEDOT:PSS con l'aggiunta di glicole polietilenico (PEG) in fase di deposizione elettrochimica, un plastificante che migliora le proprietà elastiche dei bioelettrodi. Al fine di ottenere una caratterizzazione topologica dei dispositivi, si è fatto uso di un Microscopio a Forza Atomica (AFM). Infine, è stata elaborata una metodologia per caratterizzare i dispositivi sotto l'azione di uno stress meccanico molto ricorrente nelle applicazioni mediche. Si è constato che gli spettri di impedenza dei bioelettrodi possono essere ragionevolmente descritti da un circuito equivalente formato da una resistenza in serie ad una capacità. I parametri ricavati tramite questo modello sembrano suggerire inoltre un'analogia quantitativa nel comportamento del PEDOT:PSS e del PEDOT:PSS:PEG.

Novel asymmetric geopolymer membranes for oil/water emulsions separation

In this study, it was investigated the possibility of using a geopolymeric membrane as an alternative to the expensive ceramic ones. The goal was to synthesise a low-cost membrane made entirely of geopolymer that can perform equally to commercial membranes. This study initially investigated the feasibility of preparing a microporous support suitable for microfiltration through casting and pressing techniques. Subsequently, a selective geopolymeric layer was developed and deposited on the support, with the capability to operate within the microfiltration range and to effectively separate oil from oil-water emulsions. In order to evaluate the performance, the properties of the geopolymeric supports obtained through pressing were carefully evaluated during the experimentation phase investigating the effect of varying parameters such as sodium silicate content, water content, and applied pressure. The results obtained from these evaluations showed that it is possible to produce supports with excellent porosity and highly controlled narrow pore size distributions. The most promising geopolymeric pressed support was then used for the deposition of a selective layer on its surface. Following physical characterization, it was confirmed that the resulting geopolymer membrane was suitable for use in the microfiltration range. Subsequently, the membrane was tested for its ability to separate oil from water using various emulsions prepared with different surfactants at different concentrations and pH. The results revealed that the fluxes were highly dependent on the electrostatic interaction between the membrane and the emulsion, with best results being obtained with emulsions prepared using anionic surfactants. The rejection rate of the membrane was also found to be extremely high, with values over 95%, comparable to a commercial ceramic membrane. This suggests that geopolymer membranes are suitable alternatives to ceramic membranes, offering the added benefits of lower cost and reduced environmental impact during production.

Development And Shelf-life Determination Of Pasteurized, Microfiltered, Lactose Hydrolyzed Skim Milk.

The segment of the world population showing permanent or temporary lactose intolerance is quite significant. Because milk is a widely consumed food with an high nutritional value, technological alternatives have been sought to overcome this dilemma. Microfiltration combined with pasteurization can not only extend the shelf life of milk but can also maintain the sensory, functional, and nutritional properties of the product. This studied developed a pasteurized, microfiltered, lactose hydrolyzed (delactosed) skim milk (PMLHSM). Hydrolysis was performed using β-galactosidase at a concentration of 0.4mL/L and incubation for approximately 21h at 10±1°C. During these procedures, the degree of hydrolysis obtained (>90%) was accompanied by evaluation of freezing point depression, and the remaining quantity of lactose was confirmed by HPLC. Milk was processed using a microfiltration pilot unit equipped with uniform transmembrane pressure (UTP) ceramic membranes with a mean pore size of 1.4 μm and UTP of 60 kPa. The product was submitted to physicochemical, microbiological, and sensory evaluations, and its shelf life was estimated. Microfiltration reduced the aerobic mesophilic count by more than 4 log cycles. We were able to produce high-quality PMLHSM with a shelf life of 21 to 27d when stored at 5±1°C in terms of sensory analysis and proteolysis index and a shelf life of 50d in regard to total aerobic mesophile count and titratable acidity.

Mechanical Properties And Fracture Dynamics Of Silicene Membranes.

As graphene has become one of the most important materials, there is renewed interest in other similar structures. One example is silicene, the silicon analogue of graphene. It shares some of the remarkable graphene properties, such as the Dirac cone, but presents some distinct ones, such as a pronounced structural buckling. We have investigated, through density functional based tight-binding (DFTB), as well as reactive molecular dynamics (using ReaxFF), the mechanical properties of suspended single-layer silicene. We calculated the elastic constants, analyzed the fracture patterns and edge reconstructions. We also addressed the stress distributions, unbuckling mechanisms and the fracture dependence on the temperature. We analysed the differences due to distinct edge morphologies, namely zigzag and armchair.

Effects Of Sterilization Methods On The Physical, Chemical, And Biological Properties Of Silk Fibroin Membranes.

Silk fibroin has been widely explored for many biomedical applications, due to its biocompatibility and biodegradability. Sterilization is a fundamental step in biomaterials processing and it must not jeopardize the functionality of medical devices. The aim of this study was to analyze the influence of different sterilization methods in the physical, chemical, and biological characteristics of dense and porous silk fibroin membranes. Silk fibroin membranes were treated by several procedures: immersion in 70% ethanol solution, ultraviolet radiation, autoclave, ethylene oxide, and gamma radiation, and were analyzed by scanning electron microscopy, Fourier-transformed infrared spectroscopy (FTIR), X-ray diffraction, tensile strength and in vitro cytotoxicity to Chinese hamster ovary cells. The results indicated that the sterilization methods did not cause perceivable morphological changes in the membranes and the membranes were not toxic to cells. The sterilization methods that used organic solvent or an increased humidity and/or temperature (70% ethanol, autoclave, and ethylene oxide) increased the silk II content in the membranes: the dense membranes became more brittle, while the porous membranes showed increased strength at break. Membranes that underwent sterilization by UV and gamma radiation presented properties similar to the nonsterilized membranes, mainly for tensile strength and FTIR results.