Electronic transport properties of electrically doped cytosine‐based optical molecular switch with single‐wall carbon nanotube electrodes

This study represents an empirical model of cytosine‐based optical molecular switch. This possible biomolecular switch has been designed using the first principle approach which is based on density functional theory and non‐equilibrium Green''s function. The quantum‐ballistic transport property and current–voltage (I–V) characteristics of cytosine‐based optomolecular switch have been investigated at 25 THz operating frequency. The influence of highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gaps on the electronic transmission and I–V characteristics has been discussed in detail. The aim of this study is to highlight the minimum conformational change during a single ON–OFF switching cycle. The biomolecule comprises switching behaviour when converts from straightened to twisted form during photo‐excitement. The straightened and twisted forms of the molecule are represented as logic ‘0’ and logic ‘1’, respectively. This p and n regions of this switch has been made using electrical doping process. The current through the twisted form of the cytosine biomolecule is ∼1000 times higher than the straightened form. The maximum switching ratio 62.1 is obtained at 1 V bias. The origin of the switching behaviour of the biomolecule can be interpreted by quantum–ballistic transport model along with HOMO–LUMO gaps.Inspec keywords: ballistic transport, organic compounds, Green''s function methods, ab initio calculations, density functional theory, molecular biophysics, optical switches, single‐wall carbon nanotubes, electrochemical electrodesOther keywords: electrical doping process, cytosine biomolecule, electronic transport properties, single‐wall carbon nanotube electrodes, cytosine‐based optical molecular switch, density functional theory, electronic transmission, HOMO‐LUMO gaps, current–voltage characteristics, biomolecular switching behaviour, quantum–ballistic transport property model, electrically doped cytosine‐based optical molecular switch, first principle approach, nonequilibrium Green''s function, I‐V characteristics, highest occupied molecular orbital–lowest unoccupied molecular orbital gaps, single ON–OFF switching cycle, photoexcitement, frequency 25.0 THz, voltage 1.0 V, C     

High‐performance immunosensor for urine albumin using hybrid architectures of ZnO nanowire/carbon nanotube

In this work, the authors reported the hybrid architecture of carbon nanotube (CNT)–zinc oxide (ZnO) nanowire as a multi‐functional probe in amperometric immunosensor for the detection of urine albumin. Low‐cost substrate such as glass is possible because of novel low‐temperature growth process of CNT/ZnO nanowires as a multi‐function electrode in this sensor. Based on Schottky like behaviour this structure exhibit excellent high current density to achieve higher performance. Measurement of urine albumin is a new way for early detection of diabetic and also low concentration of it in culture media is also considered in order to verify the conversion of stem cells to liver cells. Human albumin serum antibody is used as a selective and sensitive part. The amperometric performance of immunosensor is studied and showed excellent performance for detection of albumin in urine samples. Very high linear range (from 3.3 ng/µl to 3.3 mg/µl) with a correlation coefficient of 0.825 and low detection limit (3.3 ng/µl or 4.96 × 10⁻⁸ mol l⁻¹) are the main characteristics of this sensor. Due to the high dynamic range and sensitivity, this sensor was also used in medical diagnosis and biomedical applications.Inspec keywords: biosensors, zinc compounds, wide band gap semiconductors, nanosensors, nanowires, carbon nanotubes, amperometric sensors, II‐VI semiconductors, electrochemical electrodes, Schottky effect, current density, chemical variables measurementOther keywords: amperometric immunosensor, low‐temperature growth process, current density, multifunction electrode probe, nanowire‐carbon nanotube architectures, CNT, human albumin serum antibody detection, Schottky like behaviou, urine albumin measurement, diabetic detection, stem cell conversion, liver cell conversion, medical diagnosis, biomedical applications, ZnO‐C     

Numerical analysis in focusing characteristics of the three-dimensional trapezoidal electrodes for carbon nanotube field emitters

In this study, the focusing characteristics of three-dimensional trapezoidal focusing electrodes for carbon nanotube field emitters are analyzed by the combination of the finite-difference time-domain and particle-in-cell methods. To investigate the divergences of the electrons, the three-dimensional trajectories of the electron beams are simulated by evaluating the electrons’ positions and momentums. The divergence angles of electrons in the emitters with three-dimensional focusing electrodes are proved to be smaller than those with the conventional triode structure or with the planar focusing electrodes. Characteristics of the 4 μm-thick three-dimensional geometries (trapezoidal, rectangular and inversed trapezoidal) are compared. The 1 V biased three-dimensional trapezoidal focusing electrode is optimal in regulating the divergence of the beams and forming uniform electron spots on the anode. The average divergence angle of the electrons is limited to 0.1309 rad on the anode plane while the maximum divergence angle is 0.3236 rad.     

Complex optical index of single wall carbon nanotube films from the near-infrared to the terahertz spectral range

We retrieve the complex optical index of single-walled carbon nanotube (CNT) films in the 0.6-800 μm spectral range. Results are obtained from a complete set of optical measurements, reflection and transmission, of free-standing CNT films using time domain spectroscopy in the terahertz (THz) and Fourier transform infrared (IR) spectroscopy in the visible-IR. Based on a Drude-Lorentz model, our results reveal a global metallic behavior of the films in the IR, and confirm their high optical index in the THz range.     

A comparative study of Young’s modulus of single-walled carbon nanotube by CPMD, MD and first principle simulations

Carbon nanotubes (CNTs), due to their exceptional magnetic, electrical and mechanical properties, are promising candidates for several technical applications ranging from nanoelectronic devices to composites. Young’s modulus holds the special status in material properties and micro/nano-electromechanical systems (MEMS/NEMS) design. The excellently regular structures of CNTs facilitate accurate simulation of CNTs’ behavior by applying a variety of theoretical methods. Here, three representative numerical methods, i.e., Car–Parrinello molecular dynamics (CPMD), density functional theory (DFT) and molecular dynamics (MD), were applied to calculate Young’s modulus of single-walled carbon nanotube (SWCNT) with chirality (3,3). The comparative studies showed that the most accurate result is offered by time consuming DFT simulation. MD simulation produced a less accurate result due to neglecting electronic motions. Compared to the two preceding methods the best performance, with a balance between efficiency and precision, was deduced by CPMD.     

Computational study of the effect of carbon vacancy defects on the Young's modulus of (6, 6) single wall carbon nanotube

Most molecular dynamics (MD) simulations for single wall carbon nanotubes (SWCNT) are based on a perfect molecular material structure. The presence of vacancy defects in SWCNTs could lead to deviations from this perfect structure thus affecting the predicted properties. The present paper investigates the effect of carbon vacancy defects in the molecular structure of SWCNT on the Young's modulus of the SWCNT using MD simulations performed via Accelrys and Materials Studio. The effect of the position of the defects in the nanotube ring and the effect of the number of defects on the Young's modulus are studied. The studies indicate that for an enclosed defect with the same shape in a SWCNT structure, its position did not cause any change in the Young's modulus. However, as the number of defects increased, the predicted Young's modulus was found to decrease. For a 10 ring (6, 6) SWCNT, six vacancy defects (corresponding to a defect percentage of 2.5%) reduced the Young's modulus by 13.7%.     

The effect of environmental factors on the electrical conductivity of a single oligo-DNA molecule measured using single-walled carbon nanotube nanoelectrodes

We present an electrical conductivity study on a double-stranded DNA molecule bridging a single-walled carbon nanotube (SWNT) gap. The amine terminated DNA molecule was trapped between carboxyl functionalized SWNT electrodes by dielectrophoresis. The conductivity of DNA was measured while under the influence of various environmental factors, including salt concentration, counterion variation, pH and temperature. Typically, a current of tens of picoamperes at 1?V was observed at ambient conditions, with a decrease in conductance of about 33% in high vacuum conditions. The counterion variation was analyzed by changing the buffer from sodium acetate to tris(hydroxymethyl) aminomethane, which resulted in a two orders of magnitude increase in the conductivity of the DNA. A reversible shift in the current signal was observed for pH variation. An increase in conductivity of the DNA was also observed at high salt concentrations.     

Review of the systems biology of the immune system using agent‐based models

The immune system is an inherent protection system in vertebrate animals including human beings that exhibit properties such as self‐organisation, self‐adaptation, learning, and recognition. It interacts with the other allied systems such as the gut and lymph nodes. There is a need for immune system modelling to know about its complex internal mechanism, to understand how it maintains the homoeostasis, and how it interacts with the other systems. There are two types of modelling techniques used for the simulation of features of the immune system: equation‐based modelling (EBM) and agent‐based modelling. Owing to certain shortcomings of the EBM, agent‐based modelling techniques are being widely used. This technique provides various predictions for disease causes and treatments; it also helps in hypothesis verification. This study presents a review of agent‐based modelling of the immune system and its interactions with the gut and lymph nodes. The authors also review the modelling of immune system interactions during tuberculosis and cancer. In addition, they also outline the future research directions for the immune system simulation through agent‐based techniques such as the effects of stress on the immune system, evolution of the immune system, and identification of the parameters for a healthy immune system.Inspec keywords: reviews, cancerOther keywords: review, system biology, agent‐based models, immune system, vertebrate animals, human beings, disease, gut nodes, lymph nodes, tuberculosis, cancer     

A comparative study on the domain switching characteristics of near stoichiometric lithium niobate and lithium tantalate single crystals

For pure SLN and SLT crystals the coercive field measured from ferroelectric hysteresis loop was found to be independent of ramp rate. Decreased lithium concentration in pure SLN samples, the coercive field and internal field are strongly enhanced. Nb_Li antisites are the major contribution to the internal field. Coercive field depends strongly on the ramp rate in case of MgSLN and MgSLT samples, because of domain pinning. The coercive field is considerably reduced in Mg doped SLN and SLT compared to pure samples, indicating that the switching fields are strongly dependent on the nonstoichiometry of the crystals. The coercive field values were found to be constant under multiple cycling in case of Mg (1 mol%) doped SLN crystal. A strong correlation is found to exist between coercive field value and the Curie temperature.     

Modification of rheological and filtration characteristics of water‐based mud for drilling oil and gas wells using green SiO2 @ZnO@Xanthan nanocomposite

In this study, a green, simple and economical approach was used to synthesise the SiO₂ @ZnO@Xanthan nanocomposite (NC) to modify the rheological and filtration characteristics of the water‐based drilling mud. The green synthesised NCs were identified using scanning electron microscopy, energy dispersive X‐ray spectroscopy, elemental mapping, X‐ray diffraction and UV–Vis analytical techniques. Additionally, the effect of SiO₂ @ZnO@Xanthan NCs on the filtration and rheological properties of mud including apparent viscosity, plastic viscosity, yield point, gel strength, mud cake and fluid loss was investigated. The obtained results confirmed that the synthesised NCs effectively improved the rheological properties of drilling mud, and considerably decreased its fluid loss and filter cake by about 54 and 92.5%, respectively. The results highly recommend the SiO₂ @ZnO@Xanthan NC as an excellent additive to improve the rheological properties, and reduce the fluid loss and the filter cake of the drilling mud.Inspec keywords: X‐ray diffraction, scanning electron microscopy, nanofabrication, additives, nanocomposites, X‐ray chemical analysis, drilling (geotechnical), yield point, rheology, filtration, industrial economics, silicon compounds, zinc compounds, ultraviolet spectra, visible spectra, nanofluidics, gelsOther keywords: rheological properties, fluid loss, drilling mud, filtration characteristics, water‐based mud, green approach, economical approach, X‐ray spectroscopy, mud cake, apparent viscosity, oil‐gas wells, nanocomposite synthesis, scanning electron microscopy, energy dispersive X‐ray spectroscopy, elemental mapping, X‐ray diffraction, Uv–Vis spectroscopy, plastic viscosity, yield point, gel strength, additive, SiO₂ , ZnO     

Evaluation of the effective mechanical properties of single walled carbon nanotubes using a spring based finite element approach

The development of a finite element formulation that is appropriate for the computation of Young’s and Shear modulus of single walled carbon nanotubes (SWCNTs) is the purpose of this paper. The method utilizes the atomistic microstructure of the nanotubes. According to the three-dimensional atomic nanostructure of SWCNTs, nodes are defined at the atom locations. Appropriate spring-type elements interconnect these nodes to simulate properly interatomic interactions. This approach is implemented via the use of three-dimensional spring-like elements each node of which obeys to three translations and three rotations. In this way, molecular mechanics theory can be applied directly while the atomic bonds are modeled by using exclusively physical variables such as bond stretching, bond angle bending and torsional rotation resistance force constants. With the proposed method, the Young’s and shear modulus of numerous SWCNTs were determined. The effect of the nanotube radius and thickness on the mechanical behavior of SWCNTs was tested and demonstrated. The numerical results show good agreement with other corresponding values which are available in the literature.     

Design,characterisation and drug release study of polymeric,drug‐eluting single layer thin films on the surface of intraocular lenses

To design, develop and study a novel drug delivery system for intraocular applications. The spin coating technique was applied to develop a polymeric, drug‐eluting thin film consisting of a blend of organic polymers [poly (D, L lactide coglycolide) lactide: glycolide 75: 25, PLGA and polycaprolactone, PCL] and dexamethasone on the surface of intraocular lenses (IOLs). The initial durability of the IOLs during spinning was assessed. Information about the structural and optical properties of the modified IOLs was extracted using atomic force microscopy, scanning electron microscopy and spectroscopic ellipsometry. A drug release study was conducted for 8 weeks. The IOLs were durable in spinning speeds higher than the ones used to develop thin films. Single‐layer thin films were successfully developed on the optics and the haptics of the lenses. The films formed nanopores with encapsulated aggregates of dexamethasone. The spectroscopic ellipsometry showed an acceptable optical transparency of the lenses regardless of the deposition of the drug‐eluting films on their surface. The drug release study demonstrated gradual dexamethasone release over the selected period. In conclusion, the novel drug‐eluting IOL system exhibited desired properties regarding its transparency and drug release rate. Further research is necessary to assess their suitability as an intraocular drug delivery system.Inspec keywords: ellipsometry, encapsulation, nanoporous materials, spin coating, polymer blends, biodegradable materials, surface treatment, polymer films, atomic force microscopy, transparency, nanomedicine, durability, scanning electron microscopy, drug delivery systemsOther keywords: drug release, intraocular lenses, intraocular applications, spin coating technique, modified IOLs, spectroscopic ellipsometry, dexamethasone release, transparency, drug release rate, intraocular drug delivery system, drug‐eluting IOL system, polymeric drug‐eluting single‐layer thin films, optical properties, structural properties     

An electrochemical sensor based on 1-benzyl-4-ferrocenyl-1H-[1,2,3]-triazole/carbon nanotube; detection of D-penicillamine in the presence of tryptophan

A glassy carbon electrode modified with 1-benzyl-4-ferrocenyl-1H-[1,2,3]-triazole (BFT) and carbon nanotubes have been applied to the electrocatalytic oxidation of D-penicillamine (D-PA) which reduced the overpotential by about 470 mV with obviously increase the current response. Due to its strong electrocatalytic activity towards D-PA, the modified electrode can resolve the overlapped voltammetric waves of D-PA and tryptophan (TRP) into two well-defined voltammetric peaks with peak-to-peak separation in potentials of about 270 mV. This property allows to selective determination of D-PA in the presence of TRP. The transfer coefficient (a) for the electrocatalytic oxidation of D-PA and diffusion coefficient of this substance under the experimental conditions were also investigated. In phosphate buffer solution (PBS) of pH 8.0, the oxidation current increased linearly with two concentration intervals of D-PA, one is 1.0 to 10.0 μM and, the other is 10.0 to 800.0 μM. The detection limit (3σ) obtained by square wave voltammetry (SWV) was 0.1 μM. The proposed method was successfully applied to the determination of D-PA, and TRP in real samples.     

First principle calculation of physical properties of barium based chalcogenides BaM4S7 (M = Ga,Al); a DFT,DFT-D and hybrid functional HSE06 study

The electronic structure, elastic and optical properties have been calculated for the novel nonlinear optical (NLO) crystals BaQ₄S₇ (Q = Ga, Al) using plane wave pseudo-potential density functional theory (DFT) method as implemented in CASTEP and ABINIT codes. In this study we used both hybrid HSE06 and DFT-D functionals with GGA approximation. These NLO compounds, which belong to the mm2 point group, are particularly interesting because of their transparency in the mid-infrared region and wide energy band gap. We present results for electronic structure, elastic tensor coefficients, refractive indices and second order nonlinear optical susceptibilities. The calculated energy band gap and frequency dependent refractive indices as well as the NLO coefficients of BaGa₄S₇ are in good agreement with the experimental values. With no reported theoretical or experimental energy band gap and optical properties of BaAl₄S₇, we present for the first time its electronic structure and above mentioned optical coefficients. This compound has higher direct band gap with 3.74 eV, better optical birefringence and second-order NLO coefficients than most NLO compounds. The second-order NLO coefficients for BaAl₄S₇ have been calculated as d₃₁ = 3.15 pm/V, d₃₁ = 2.20 pm/V, d₃₃ = −6.31 pm/V.     

Amalgamation and application of nano chitosan cross‐linked with fish scales based activated carbon as an adsorbent for the removal of reactive dye (RB9)

The extensive discomfort in the expulsion of toxic pollutants even at mild concentrations has demanded the need for prompt methods for the evacuation of dyes and heavy metals. The effective method for depuration of dye from the effluent is by sorption. Chitosan is a bio‐polymer which is gaining an increasing interest as one of the sorbents. It was obtained from the crab shells by undergoing several chemical processes and used as an adsorbent for dye, metal removal and also for pharmaceutical purposes. Cross linking it with other co polymers will increase the capacity of adsorption to a maximum level. Fish scales are considered to be a major waste in the food industry and since it takes a long time for decomposing it is considered to be one of the pollutants. Hence it is utilised by converting it into activated carbon by preliminary treatment and into a muffle furnace. The obtained activated carbon is combined with chitosan by using a cross linker and utilised for adsorption mechanism. To analyse the effect of chitosan cross linked with activated carbon obtained from fish scales in adsorption of dye Reactive Blue 9 (RB9) to evaluate the adsorption studies, kinetics, mass transfer studies, thermodynamics of the bio adsorbent.Inspec keywords: dyes, wastewater treatment, effluents, mass transfer, activated carbon, adsorption, polymer blends, water pollution control, thermodynamics, reaction kinetics, furnaces, recycling, industrial waste, waste recovery, food processing industry, pharmaceutical industry, renewable materials, nanoparticles, toxicologyOther keywords: fish scales, activated carbon, reactive dye removal, toxic pollutants, heavy metals, bio‐polymer, nanochitosan, bio adsorbent, amalgamation, RB9 dye, industrial effluent, crab shells, adsorption method, pharmaceutical purposes, copolymers, food industry waste, waste recovery, recycling process, muffle furnace, reaction kinetics, mass transfer, thermodynamic analysis, ReactiveBlue 9, wastewater treatment, water pollution control, C     

Phytosynthesis of Cu/rGO using Euphorbia cheiradenia Boiss extract and study of its ability in the reduction of organic dyes and 4‐nitrophenol in aqueous medium

For the first time, copper nanoparticles (Cu NPs) superficially deposited on reduced graphene oxide (rGO) using Euphorbia cheiradenia Boiss leaf aqueous media. A beneficial series of analytical methods was used to characterise E. cheiradenia Boiss leaf extract and involved nanostructures. The Cu/rGO nanocomposite (NC) obtained from the conversion of Cu²⁺ ions to Cu NPs and GO to rGO undergoes the plant extract and used as a heterogeneous and reusable nanocatalyst for the destruction of 4‐nitrophenol, rhodamine B, methylene blue, methyl orange and congo red using sodium borohydride at ambient temperature. In addition, Cu/rGO NC has reusability for many times in the reduction reactions with no decreasing of its catalytic capability.Inspec keywords: catalysts, nanofabrication, nanocomposites, dyes, nanoparticles, reduction (chemical), copper, graphene compoundsOther keywords: phytosynthesis, organic dyes, reusable nanocatalyst, Euphorbia cheiradenia Boiss extract, 4‐nitrophenol, nanoparticles, graphene oxide, nanocomposites, methylene blue, methyl orange, congo red, sodium borohydride, catalytic capability, Cu‐CO