Scientia Iranica
Volume:24 Issue: 6, Nove-Dec 2017

We propose an active plasmonic device based on graphene. By using a diffractive grating on silicon, highly confined plasmonic waves in monolayer graphene are efficiently excited. The high electric field of the surface plasmons near the graphene layer makes them ideal for use in biosensors, where a very small change in refractive index should be detected. A small change in the refractive index of surroundings medium, induces a large change in resonant wavelength. The spectral shift per refractive index unit (∆λ0/RIU) of the sensor is considerable and exceeding 2000 nm/RIU with a narrow line width spectral of the plasmon resonances. The figure of merit for this sensor is approximately equal to 14.2 and electrical tuning can be achieved by adjusting the Fermi level in graphene. Therefore, this grating plasmonic structure is highly sensitive and can be used in high resolution biosensing applications.

DNA nanotechnology is a purist’s approach to biomolecular engineering. The field aims to create molecular structures and devices through the exclusive use of DNA as an engineering material. On the other hand, DNA Spintronics as a DNA nanotechnology field uses the electron spin to store and process information. In this work, we have used the Peyrard-Bishop-Holstein model combined with spin-orbit interaction for studying the spin transfer mechanism in DNA nanowires. In this work, the electrical currents corresponding to the spin up and spin down electrons obtain directly using the Hamiltonian equations of system. We could obtained the best functional ranges for external agents such as magnetic and electrical fields and surroundings temperature for applying in spintronics applications. By considering the simultaneous effect of parameters, we have determined the islands with pure spin current. But, the considerable result is where we have applied the time periodic magnetic field and observe the characteristic peaks in polarization diagram. These peaks can be used for information coding as zero-one codes. Therefore, one could construct DNA nanowires which filter the spin current, create the nearly pure spin currents and act as a spintronics device for process and transfer the information.

We present a plasmonic switch based on anisotropic structure consisting of graphene and silicon layers, like one-dimensional photonic crystal. The plasmonic wave in this switch is propagated inside the MgF2 core surrounded by two periodic arrays of graphene / silicon. Changing the chemical potential of graphene leading to the change of permittivity of anisotropic array, we can adjust the propagation length of plasmonic wave. The obtained results show that, at the frequency of 30 THz with adjusting the chemical potential of graphene, the chemical potential of 0.4 eV and 0.2 eV can be obtained for the ON_state and OFF state, respectively. Also, the ON/OFF ratio is about 24.

Nanofibrous composite scaffolds based on Tecophilic (TP) and gelatin (gel) were electrospun and further modification of their surfaces was performed by adsorption of gelatin or fibronectin biomolecules. The ability of coated scaffolds to alter the proliferation rate of smooth muscle cells (SMCs) was investigated via various assays and compared to cell proliferation on non-coated scaffolds. The results confirmed the potential of both coated and non-coated composite scaffolds to support SMC growth. Although, the presence of fibronectin increased the proliferation, adsorbed gelatin could reduce the proliferation of SMCs. The success of a tissue engineered vascular graft depends on the ability of the scaffold to control the proliferation rate of SMCs and thus our study provides a better insight towards the fabrication of functional constructs for vascular regeneration.

In this work, hybrid of silica nanoparticles (NPs) with sulfonated copolymer has been prepared in order to improve the copolymer properties for enhanced oil recovery (EOR). Some tests are done to find the effectiveness of injecting fluid on recovery factor (RF), such as; contact angle (CA), interfacial tension (IFT), inherent viscosity and eventually Micro-Model (MM) flooding. In CA test, wettability alteration from oil-wet (OW) to water-wet (WW) is reached by sedimentation and adsorption of NPs on the rock slice. In addition, IFT reduction is obtained by increasing the NaCl concentration. The viscosity change is investigated for the hybrid and copolymer under simulated high-temperature oil reservoir conditions. It is found that silica NPs-copolymer hybrid exhibits better inherent viscosity and thermal stability than copolymer alone. At MM flooding, more RF and produced oil in water (O/W) emulsion is obtained from hybrid respect to polymer alone. Hybrid injection results in IFT reduction, increment in viscosity and O/W emulsion formation that cause enhancement in capillary number (Nca) and RF and subsequently reduction in residual oil saturation. Therefore, NPs-copolymer hybrid could be a much better candidate than even high-performance polymer solutions for EOR process.

For a successful bladder tissue repair and reconstruction, fabrication of scaffolds with proper biochemical and biomechanical characteristics is necessary. Decellularized bladder tissue has been proposed in previous studies as a gold standard material for scaffold fabrication. However, the weak mechanical properties for such load-bearing tissue has remained a challenge. Incorporation of both biological and synthetic materials has been known as an effective strategy for improving mechanical and biological properties of the scaffolds. In present work, a simple process is developed to fabricate hybrid hydrogel scaffolds with a biomimetic architecture from the natural urinary bladder extracellular matrix (ECM) and synthetic polycaprolactone (PCL) nanofibers, in order to obtain a scaffold with optimized mechanical and biological properties for bladder tissue engineering. To this gaol, the ECM gel was derived from rat bladder and the electrospun PCL nanofibers was embedded within the gel, followed by incubating the composite to shape the hybrid hydrogel. These reinforced scaffolds showed more structural integrity and mechanical stability. The introduced concept of nanofiber-reinforced ECM can be applied as a promising platform in engineering of bladder or other load-bearing soft tissues.

Titanium nitride-carbon nanocomposites have been synthesized by the reaction of TiCl4 and NaN3 in supercritical benzene medium that also serves as a carbon source. The as-prepared precursor has been subjected to different heat treatments under ammonia and nitrogen atmospheres. The structure and chemical composition of the synthesized TiN-C nanocomposites are studied by X-ray diffraction (XRD) and CHN elemental analysis. Meanwhile, the nature of carbonaceous species and the respective carbon phase transitions during supercritical process and following heat treatments are further investigated by Raman spectroscopy, time of flight secondary ion mass spectrometry (ToF-SIMS), and their charge-discharge characteristics with respect to lithium storage. After 10 h NH3-treatment at 1000 ˚C carbonaceous phase transforms to graphene layered structure. The highly efficient mixed TiN conducting network and the internal defects between G layers induced by nitrogen doping improve rate capability and cycling performance of G sheets and provides a specific capacity of 381 mAh g-1 at charge/discharge (C/D) rate of 0.2 C. The enhanced electrochemical performance of the SIV nanocomposite is mainly due to improving the electronic/ionic conductivity and reducing charge transfer coefficient and increasing electrochemical surface area that are resulted from anchoring of TiN nanoparticles on graphene sheets.

We have prepared Nanoporous Graphene/Silica Nanohybrid and demonstrated its better Pickering emulsion properties for Chemical Enhanced Oil Recovery in comparison to the similar Silica Nanohybrid with single-walled carbon nanotube. The samples were characterized with X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM) and Thermal Gravimetry Analysis (TGA).
Emulsion phase morphology was investigated with optical microscopic image. Evaluation results demonstrated that the best samples are 70% Nanoporous Graphene/SiO2 (both methods) and 70% SWCNT/ SiO2 Nano hybrid (method 1). Contact angle measurement results showed that the 70% Nanoporous Graphene/SiO2Nanohybrid (method 2) is more effective for improvement of the stone reservoir wettability alteration from oil-wet to water-wet. Interfacial tension results indicate that the maximum amount is related to the injection of water and the minimum amount is related to the injection of Nanofluid of 70% Nanoporous Graphene/SiO2 Nano hybrid (method 2). This result indicates preference of 70% Nano porous Graphene/SiO2 Nanohybrid (method 2) for decreasing the interfacial tension in comparison to the other samples.

Er3+Yb3 co-doped titanium dioxide upconversion nanoparticles were synthesized by Sol-gel method. White upconversion emissions were observed after excitation of nanoparticles with 980 nm Near-Infrared laser diode. Upconversion emissions consist of red (640-690 nm), green (520-570 nm) and blue (408 nm) emissions. Ultraviolet upconversion emissions were also detected with wavelength about 210 nm. Ultraviolet emissions are probably the results of relaxation from 2I13/2 (220 nm) and 2L15/2 (210 nm) states to 4I15/2. Visible and ultraviolet emissions of these nanoparticles can be used in photodynamic therapy. High penetration of Near-Infrared light into the body tissue makes these nanoparticles appropriate for aiming tumors in deeper tissues in comparison with older methods of photodynamic therapy.

The Cu-0.5Co/WC nano-composite coating was synthesized on CP-copper substrate using direct current (DC) electrodeposition method. At this work, it was tried to increase the hardness of surface without considerable degradation of copper's particular physical properties such as electrical conductivity. The effect of current density on microstructural homogeneity, hardness, fracture toughness and electrochemical behavior of coating was investigated. The copper plates with the purity of 99.99% were used as electrodes. The electrolyte consists of tungsten carbide particles (30 g/l), copper sulfate (200 g/l), sulfuric acid (50 g/l), cobalt sulfate (50 g/l) and sodium dodecyl sulfate (SDS) (0.3 g/(g of WC)) as surfactant. The particle size of tungsten carbide powder was in the range of 40-70 nm. The distribution of tungsten carbide particles in coating was studied using FESEM. Micro-hardness measurement was performed in Vickers scale. The fracture toughness of coating was determined by Vickers indentation test. The corrosion resistance of the electrodeposited Cu-Co and Cu-Co/WC nano-composite coatings was evaluated by polarization studies. Referring to results, the use of optimum current density value (60 mA/cm2) during the electrodeposition process improves hardness and corrosion resistance of nano-composite coating. Additionally, Cu-Co/WC composite coating shows more corrosion resistance than the unreinforced one.

Nanostructured hollow polyaniline (PANI) capsules are good candidates for encapsulation of corrosion inhibitors and pH-responsive release when incorporated into organic coatings. In previous work the corrosion protection performance of PANI capsules containing organic inhibitor 2-Mercaptobenzothiazole (MBT) was demonstrated. The present work studies the influence of capsule concentrations (i.e. 0.3, 1 and 2 wt.%) on the corrosion protection properties of the coating system. Anti-corrosion properties of different coatings were compared by means of Electrochemical Impedance Spectroscopy (EIS), and Scanning Vibrating Electrode Technique (SVET). MBT loaded PANI capsules in epoxy ester coating on AA2024-T3 substrate allows for a self-healing effect to be obtained during the corrosion process. The results showed that the concentration of MBT loaded PANI capsules greatly influence the corrosion protection properties of the coatings, and the best corrosion protection performance was observed for the coating system containing 1 wt% PANI capsules. The impedance value of the scratched area of this coating after 7 days of immersion was one order of magnitude higher than that of the control sample.

Thin films of Fe73.1Cu1Nb3.1Si14.7B8.2 alloy having thickness of 200, 500 and 800 nm have been deposited by RF sputtering. Their magnetic properties have been characterized using alternating gradient field magnetometer (AGFM) and vibrating sample magnetometer (VSM). The effects of residual stresses investigated by nanoindentation experiments were conducted on as-deposited samples. It is observed that the coercivity of as-deposited films is inversely proportional to the thickness in relation with the residual stress induced during sputtering.

ZnO nanostructures were produced with an innovative and simple vacuum thermal evaporation method with evaporating Zn in the presence of strong static electric and magnetic fields perpendicular to each other. These evaporated Zn thin films were oxidized in the furnace to obtain ZnO. In order to investigate the effects of magnetic field on ZnO nanostructures in this method, two different setups with different magnetic field strengths were assembled. Morphology and structure of ZnO thin films in both setups were investigated by micrographs prepared by field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) analysis. Results show that grown nano rods of ZnO in both setups are blade-like and match-like. Increase in magnetic field, changes the dominant type of nano rods from blade-like in weaker magnetic field to match-like in stronger magnetic field. Also increasing magnetic field strength causes different crystalline orientation in ZnO nanostructures. The results suggest that morphology and structure of ZnO thin films are affected by applying magnetic fields with different strength during deposition of Zn in this innovative method.

n this paper we attempt to present a multilayered structure biosensor. A graphene-based surface plasmon resonance (SPR) biosensor is considered as a structure which offers the enhancement of sensitivity in comparison with the conventional biosensors. The sensitivity improvement caused by the presence of graphene is discussed through monitoring of the biomolecular interactions and following that the refractive index (RI) changes. For this purpose, a RI change which is increased during the course of biomolecular interactions is considered from 1.462 to 1.52. Our numerical results show that the proposed SPR biosensor with a graphene layer can provide a better sensitivity due to the field distribution at the binding region. This paper investigates the sensitivity enhancement factor (SEF) according to the S-parameters and the effects of design parameters such as the thicknesses of gold and graphene layers and the refractive index change during the course of DNA hybridization in this biosensor.

In this paper, embedding plasmonic nanoparticles inside the solar cell’s active layer both in a periodic and a random manner is extensively investigated. The reason behind this study is to investigate optical mechanisms inside the active layer as a consequence of nanoparticle inclusion as well as comparing periodicity versus randomness in such structures, where the intended maximization of the ultra-broadband absorption renders the analysis complicated. To perform such study, an effective refractive index analysis is employed to simultaneously covering of the influential parameters. The results show that although fully periodic structures are more desirable in narrow-band applications such as e.g. grating-assisted waveguide coupling; random inclusions of plasmonic nanoparticles in the solar cell’s active layer yield a much higher optical absorption. Furthermore, random inclusions of nanoparticles are easier and much cheaper relative to periodic inclusion to implement in solar cell fabrication.

Alpha-synuclein (α-Syn) is an abundant protein in the brain with high tendency to convert into toxic aggregated forms that are involved in neurons degeneration in Parkinson's patients (PD). The conversion of α-Syn toward toxic aggregates may associate with bio-membranes and the interaction between α-Syn and bio-mimic liposomes can trigger the neurotoxicity. Some inhibitors of α-Syn aggregation are potential drugs to cure PD; however, they have low stability and solubility at physiological conditions. Using nano-carriers such as nanoliposomes may overcome such defects. Nevertheless, there are few studies on nanoliposomes effects on neuronal cells and α-Syn. Herein; we investigated the neurotoxicity and also fibrinogenesis of neutral charged nanoliposomes. Thin layer evaporation method and the Mini-Extruder set were employed to formulate the nanoliposomes from Dipalmitoylphosphatidylcholine to the size of ≤ 100 nm. Fibrillation and also cytotoxicity of α-Syn treated with different concentrations of nanoliposome were measured by different assays. Neither neurotoxicity nor fibril induction were observed when α-Syn treated with different concentrations of nanoliposome (35-3000 µM). These results well indicated that nanoliposome at the concentrations, which are needed to drug delivery, not only be able to prevent fibrillation process, but also have no considerable toxic effects on the neural cells.

In recent times, single layer graphene oxide (GO) has been of intense interest for a broad spectrum of applications. Size and surface charge of GO sheets are two key factors in the most of these fields. These structural properties can be tuned by adjusting pH manipulating the content of oxygen-containing groups. Furthermore, the pH value extremely affects on the surface chemistry and functional groups of GO sheets which are crucial in providing a high stable solution and chemical activity of particles. In this study, Graphene oxide is synthesized by improved hummer method and characterized by XRD, AFM, FTIR, DLS and zeta potential. pH value can be tuned trough titration with NaOH and HCl and effect of pH on GO dispersion stability and optical properties is investigated.