An ultrasensitive electrochemical aptasensor based on a single-stranded aptamer-Au@Fe-MIL-88 complex using methylene blue as an electrochemical probe for insulin detection.

This work introduces an electrochemical aptasensor based on a single-stranded aptamer-Au@Fe-MIL-88 complex for sensitive and selective determination of insulin using differential pulls voltammetry. Au@Fe-MIL-88 with a large surface area was synthesized and employed as a suitable substrate for immobilization of the aptamer (APT-Au@Fe-MIL-88). Methylene blue (MB), as an electrochemical probe, was intercalated into the aptamer. Graphene oxide (GO) and zinc sulfide (ZnS) were placed on the Au electrode to amplify the MB current. Also, ZnS improves the immobilization of APT-Au@Fe-MIL-88 into the aptasensor through the strong interaction of Au-S. In the presence of the insulin, MB is released from the aptamer due to DNA conformational change, and as a result, the peak intensity of the intercalated MB was decreased. Under optimal conditions, the change in the current of MB was proportional to the insulin concentration in the range of 5.0 × 10-16-5.0 × 10-11 mol L-1, with a superior ultra-low detection limit of 1.3 × 10-16 mol L-1. It was observed that the aptasensor is suitable for determining insulin in serum samples with good sensitivity and reproducibility and with recoveries ranging from 96.4 to 102.0%. The relative standard deviations (RSD) were lower than 3.8% (n = 3).

Tunable Bragg defect mode in one-dimensional photonic crystal containing a graphene-embedded defect layer.

Using the transfer matrix method, the transmission properties of defective one-dimensional photonic crystal are analyzed in the terahertz region. The defect layer is composed of a graphene-embedded dielectric layer. We investigate the variation of the defect mode's frequency as a function of graphene chemical potential for different values of incident angles. The numerical results show that the frequency of the defect mode can be tuned effectively as the chemical potential of graphene nanolayers changes using an applied gate voltage. The present results can be useful in designing tunable graphene-based photonic devices such as filters and sensors in terahertz regions.

A simple and sensitive label-free fluorescence sensing of heparin based on Cdte quantum dots.

A rapid, simple and sensitive label-free fluorescence method was developed for the determination of trace amounts of an important drug, heparin. This new method was based on water-soluble glutathione-capped CdTe quantum dots (CdTe QDs) as the luminescent probe. CdTe QDs were prepared according to the published protocol and the sizes of these nanoparticles were verified through transmission electron microscopy (TEM), X-ray diffraction (XRD) and dynamic light scattering (DLS) with an average particle size of about 7 nm. The fluorescence intensity of glutathione-capped CdTe QDs increased with increasing heparin concentration. These changes were followed as the analytical signal. Effective variables such as pH, QD concentration and incubation time were optimized. At the optimum conditions, with this optical method, heparin could be measured within the range 10.0-200.0 ng mL(-1) with a low limit of detection, 2.0 ng mL(-1) . The constructed fluorescence sensor was also applied successfully for the determination of heparin in human serum. Copyright © 2015 John Wiley & Sons, Ltd.

A tunable flat terahertz lens using Dirac semimetals: a simulation study.

We propose and design a flat and tunable terahertz lens achieved through a two-dimensional photonic crystal composed of an array of rods made of a Dirac semimetal placed in air as the background medium. The structure of interest is a graded index photonic crystal, made possible by the slight variations in the rods' radii in a direction perpendicular to the direction of the light propagation. Dirac semimetals' ability to respond to variations in their Fermi energy level manifested as a change in the refractive index provides the tunability of our proposed lens. The interaction of electromagnetic waves with the designed structure is investigated for both transverse magnetic and transverse electric polarizations using two-dimensional finite-difference time-domain method.

Investigation of the effect of noncircular scatterers on the band structure of anisotropic photonic crystal slabs.

Using the supercell approach based on the plane wave expansion method, we analyze the photonic bandgap (PBG) of square and triangular photonic crystal slabs composed of air holes in an anisotropic tellurium background with SiO(2) as cladding material. Two shapes (square and hexagonal) are considered for air holes. We discuss the maximization of the full PBG width as a function of noncircular air hole parameters, their orientation, and also slab thickness. The numerical results show that both structures represent a full PBG with noticeable width, which can be helpful for designing optical devices.

H-CoNiSe2/NC dodecahedral hollow structures for high-performance supercapacitors.

The synergistic effect between metal ions and increasing the surface area leads to the fabrication of supercapacitor materials with high capacities. It is predicted that transition metal selenide compounds will be ideal electrode materials for supercapacitors. However, the defects of poor conductivity and volume expansion of the compounds are fundamental problems that must be solved. In this work, we successfully synthesized the cobalt-nickel selenide nitrogen-doped carbon (H-CoNiSe2/NC) hollow polyhedral composite structure using ZIF-67 as a precursor. The CoSe2 and NiSe2 nanoparticles embedded in the NC polyhedral framework offer a wealth of active sites for the whole electrode. Moreover, the presence of the NC structure in the proposed composite can simultaneously lead to improved conductivity and reduce the volume effect created during the cycling procedure. The H-CoNiSe2/NC electrode provides high specific capacity (1131 C/g at 1.0 A/g) and outstanding cyclic stability (90.2% retention after 6000 cycles). In addition, the H-CoNiSe2/NC//AC hybrid supercapacitor delivers ultrahigh energy density and power density (81.9 Wh/kg at 900 W/kg) and excellent cyclic stability (92.1% of the initial capacitance after 6000 cycles). This study will provide a supercapacitor electrode material with a high specific capacity for energy storage devices.Please confirm the corresponding affiliation for the 'Ali A. Ensafi' author is correctly identified.Error during converting author query response. Please check the eproofing link or feedback pdf for details.

Tunable multichannel Fibonacci one-dimensional terahertz photonic crystal filter.

This paper proposes a multichannel terahertz optical filter based on a one-dimensional photonic crystal with a third-order Fibonacci structure, including a bulk Dirac semimetal. The tuning of the optical properties of the proposed structure has been theoretically studied as a function of the Dirac semimetals' Fermi energy. Furthermore, the effects of the Fibonacci structure's periodic number and light's incident angle on optical channels were investigated. The results reveal that changes in the Fermi energy and incident angle remarkably affect the frequency and transmission of the optical channels. Additionally, the number of optical channels increases by increasing the periodic number of the Fibonacci structure.

Valley-optical absorption in planar transition metal dichalcogenide superlattices.

In this study, we investigate the optical absorption of a planar superlattice comprising alternatively arranged two-dimensional Transition Metal DiChalcogenide semiconductors. Within a semi-classical model and using the Dirac-like equation in the presence of light interaction as a perturbation, we obtained the governing Hamiltonian. Using this Hamiltonian, we derived a fully analytical relationship for the absorption coefficient of the structure. By calculating the effective mass for different bands and using the Drude-Lorentz model, our approach is able to determine the oscillator strength and the effective refractive index of the structure. We found that the spin-orbit coupling has important effect on the absorption coefficient and energy bands where it reduces the absorption coefficient of the structure from typical value of [Formula: see text]-[Formula: see text], also the valence band experiences a significant blue shift, while the conduction band shows minor changes due to spin orbit coupling. Moreover, the role of incident light angle and light polarization were studied in details at different valleys of [Formula: see text] and [Formula: see text]. The most important finding is that by changing the polarization of incident light, it is possible to increase the absorption coefficients of [Formula: see text] and [Formula: see text] valleys by up to 30 times. For light propagation direction close to perpendicular to the plane of the superlattice, the right-circular polarization is absorbed only by [Formula: see text] valley in contrast to the left-circular polarization, which is absorbed by the [Formula: see text] valley. Our model might be used to design newly developed 2D optovalleytronic devices.

Flexible and sewable electrode based on Ni-Co@PANI-salphen composite-coated on textiles for wearable supercapacitor.

Flexible electrodes with high deformability and energy density are critical for electronic textiles. The key factor for achieving high-performance supercapacitors with superior power and energy density is the evaluation of materials that exhibit exceptional capacitive performance. Herein, we have prepared Ni-Co nanoparticles at the surface of polyaniline-salphen (Ni-Co@PS). Then, followed by casting Ni-Co@PS on a conductive carbon cloth (CC) as a substrate through a facile in-situ polymerization strategy. The morphologies of Ni-Co@PS composite were characterized by different methods such as FE-SEM, XPS, XRD, BET, and electrochemical methods. This nanocomposite showed high tolerability and a large surface area with excellent behavior as a new nanomaterial for supercapacitor application. Thus, the optimum composite designed with a metal ratio (nickel-cobalt 3:1 w/w) satisfactorily possesses a specific capacitance of up to 549.994 C g-1 (1447.2 F g-1) under 0.5 A g-1 and long-term cyclic stability featuring capacity retention of 95.9% after 5000 cycles at a current density of 9.0 A g-1. The Ni-Co@PS-CC, is a material with great potential as an electrode in asymmetric wearable supercapacitor (AWSC) apparatus, demonstrating a remarkable specific capacity of 70.01, and accompanied by an energy density of 23.46 Wh k g-1 at a power density of 800 W k g-1.

Effect of colloidal ß-cyclodextrins-Fe3 O4 magnetic nanoparticles on the chemiluminescence enhancement of luminol-Ag(III) complex for rapid and sensitive determination of cysteine in human serum.

Colloidals solution of Fe3 O4 magnetic nanoparticles (MNPs), capped with ß-cyclodextrins (ß-CD) as inclusion complexes, were found to enhance the chemiluminescence (CL) intensity of the luminol-diperiodatoargentate(III) (DPA) system. On injection of cysteine into the luminol-DPA-ß-CD-Fe3 O4 MNPs inclusion complexes system, the CL intensity is strongly enhanced. The enhanced CL signal is ascribed to the catalytic effect of Fe3 O4 MNPs capped with ß-CD, which is assumed to stabilize the CL intermediate. Based on these findings, a rapid and sensitive assay was developed for the determination of cysteine in human serum. The effects of analytical variables on the CL signal were studied and optimized. Under the optimum conditions, the CL intensity was directly proportional to the concentration of cysteine in the range 8.0 × 10(-9) -1.0 × 10(-6) mol/L. The detection limit was 2.8 × 10(-9) mol/L (3 S(b) /m) and the relative standard deviation (RSD) for 10 replicate determinations of 1.0 × 10(-7) mol/L cysteine was 3.5%. The proposed method was applied to the sensitive determination of cysteine in human serum samples, and compared with the Ellman method with satisfactory results.

Graphene-like sheets supported Fe-Co layered double hydroxides nanoflakes as an efficient electrocatalyst for both hydrogen and oxygen evolution reaction, A green investigation.

Herein, a nanohybrid material containing graphene-like sheets (GS) and Fe-Co layered double hydroxides nanoflakes (LDHs) was synthesized via simple two-step processes and named Fe-Co LDHs/GS. The Fe-Co LDHs/GS nanohybrid was characterized by various techniques. Fe-Co LDHs nanoflakes were grown on GS in Fe-Co LDHs/GS nanohybrid. The electrochemical surface area of Fe-Co LDHs/GS nanohybrid was obtained 0.05 cm2 based on the Randles-Sevcik equation. The Fe-Co LDHs/GS nanohybrid was applied as an electrocatalyst of HER and OER in a 1.0 M KOH. The electrochemical performance of Fe-Co LDHs/GS nanohybrid was surveyed by several electrochemical methods, and long-term electrochemical stability. The onset potential, overpotential at 10 mA cm-1 current density, and Tafel slope for the Fe-Co LDHs/GS nanohybrid were obtained -0.33 V, -0.43 V (vs. RHE), and 122 mV dec-1, respectively. The Fe-Co LDHs/GS nanohybrid has long-term stability over 35 h in alkaline media toward HER. Furthermore, the onset potential, overpotential at 10 mA/cm, and Tafel slope for the Fe-Co LDHs/GS nanohybrid were obtained as 1.52 V, 1.60 V (vs. RHE), and 44 mV dec-1, respectively. The Fe-Co LDHs/GS nanohybrid has long-term durability over 10 h in alkaline media toward OER.

Green application of trimetallic nickel-cobalt-molybdenum nanocomposites on 3D graphene oxide as a powerful electrocatalyst for hydrogen evolution reaction.

In-situ designing of multiple metals electrocatalysts with high active sites and performance is the main challenge for hydrogen evolution reaction (HER). So in this work, 3D-rGO was easily obtained from 2D-graphene by a simple one-step hydrothermal method to create the interspace sites and active surface area. The Ni-Co-Mo tri-metallic@3D-rGO was synthesized and fully characterized by different techniques, e.g., FT-IR, XRD, Raman, FE-SEM, TEM, EDS, mapping, ICP-OES, AFM, voltammetry, and electrochemical impedance spectroscopy. According to the FE-SEM and TEM images, the Ni-Co-Mo tri-metallic@3D-rGO has a crumpled-formed structure. The as-prepared nanocomposite has high HER performance with a low potential of -0.11 (vs. RHE) to deliver 10 mA cm-2 and Tafel slope of 68 mV dec-1 for Pt and -0.25 V (vs. RHE) to deliver 10 mA cm-2 and Tafel slope of 110 mV dec-1 for graphite counter electrode. Furthermore, the 3D structure illustrates high long-term durability in the HER process for 1000 continuous cycles and 12 h operation at -0.42 V (vs. RHE) for Pt and graphite counter electrode. It's noticeable HER performance has the synergetic effect between 3D-rGO and tri-metallic structure with high porosity and electrical conductivity, enhancing HER kinetic.

A theoretical and experimental study of polyaniline/GCE and DNA G-quadruplex conformation as an impedimetric biosensor for the determination of potassium ions.

An electrochemical aptasensor has been developed to determine K+ using electrochemical impedance spectroscopy. The polyaniline (PANI) coating was first electrodeposited on a GCE. Then, the potassium-selective aptamer [G3(T2AG3)3] was adsorbed through an electrostatic force between PANI and aptamer. In the presence of K+, the single-stranded DNA is folded into the G-quadruplex configuration, which acts as a barrier against electron transfer at the GCE surface. AFM and FE-SEM images characterize the surface morphology at each fabrication stage. As the K+ concentration increased, the charge transfer resistance (Rct) increased, and the plot of ΔRct versus the logarithm of the K+ concentration is linear over a wide range of 10 pM-60 µM with a low detection limit of 3.7 pM. Finally, the proposed sensor was used to determine K+ in water, serum, urine, and fruit samples. Moreover, the binding stability of the aptamer/PANI and K+/Aptamer/PANI and the interactions between the aptamer and PANI were analyzed through molecular dynamics simulation.

A new method based on electrospray ionisation ion mobility spectrometry (ESI-IMS) for simultaneous determination of caffeine and theophylline.

In this work for the first time, simultaneous analysis of caffeine and theophylline was done by ion mobility spectrometry (IMS) only, without a powerful separation technique (e.g., HPLC). Ion mobility spectrometry with low cost, inexpensive maintenance and very fast analysis makes an attractive technique for the simultaneous determination of the caffeine and theophylline in foodstuff samples and biological matrices. In this study, the extraction protocol using molecular imprinted polymer-solid phase extraction (MIP-SPE) was successfully used to directly extract caffeine and theophylline from real samples. The results obtained provided the detection limits of 0.2 and 0.3µgmL(-1) for caffeine and theophylline, respectively. The linear dynamic range of about two orders of magnitude was obtained for these compounds. Also, the proposed method was used to analyse various real samples of green tea and spiked human plasma, and the obtained results confirmed the capability of ESI-IMS for simultaneous detection of caffeine and theophylline.

Ion mobility spectrometry as a detector for molecular imprinted polymer separation and metronidazole determination in pharmaceutical and human serum samples.

Application of ion mobility spectrometry (IMS) as the detection technique for a separation method based on molecular imprinted polymer (MIP) was investigated and evaluated for the first time. On the basis of the results obtained in this work, the MIP-IMS system can be used as a powerful technique for separation, preconcentration, and detection of the metronidazole drug in pharmaceutical and human serum samples. The method is exhaustively validated in terms of sensitivity, selectivity, recovery, reproducibility, and column capacity. The linear dynamic range of 0.05-70.00 microg/mL was obtained for the determination of metronidazole with IMS. The recovery of analyzed drug was calculated to be above 89%, and the relative standard deviation (RSD) was lower than 6% for all experiments. Various real samples were analyzed with the coupled techniques, and the results obtained revealed the efficient cleanup of the samples using MIP separation before the analysis by IMS as a detection technique.

Simultaneous determination of codeine and noscapine by flow-injection chemiluminescence method using N-PLS regression.

A flow injection chemiluminescent (FI-CL) method has been developed for the simultaneous determination of codeine and noscapine using N-PLS regression. The method is based on the fact that kinetic characteristics of codeine and noscapine are different in the Ru(phen)(3)(2+)-Ce(IV) CL system. In flow injection mode, codeine gives broad peak with the highest CL intensity at 4.4s, whereas the maximum CL intensity of the noscapine appears at about 2.6s. Moreover, the effect of increasing H(2)SO(4) concentration was different on the CL intensity of the compounds. An experimental design, central composite design (CCD), was used to realize the optimized variables such as Ru(II) and Ce(IV) concentrations for the both compounds. At the optimized condition, a three-way data structure (samples, H(2)SO(4) concentration, time) was constructed and followed by N-PLS regression. The number of factors for the N-PLS regression was selected based on the minimum values for the root mean squared error of cross validation (RMSECV). The proposed method is applied to the simultaneous quantification of codeine and noscapine in the pharmaceutical preparations.

Chemiluminescence determination of promazine in human serum and drug formulations using Ru(phen)3(2+)-Ce(IV) system and a chemometrical optimization approach.

A new chemiluminescence (CL) method using flow injection has been described for the rapid and sensitive determination of promazine hydrochloride (PMH). The method is based on the CL reaction of PMH with tris(1,10 phenanthroline)ruthenium(II), [Ru(phen)3(2+)] and Ce(IV) in sulfuric acid medium. Effects of chemical variables were investigated employing central composite design and response surface methodology. Under the optimum conditions, the CL intensity was proportional to the concentration of the drug in solution over the ranges 0.020-0.32 and 0.32-32 microg/mL. The limit of detection (signal-to-noise ratio = 3) was 0.012 microg/mL. The method was applied successfully to the determination of PMH in drug formulations and human serum (recovery percentages between 96.7 and 105.0%). The relative standard deviation for 11 replicate determinations of 1.5 microg/mL of PMH was 1.7%. The minimum sampling rate was 100 samples per hour.

An ancient plant for the synthesis of a novel carbon dot and its applications as an antibacterial agent and probe for sensing of an anti-cancer drug.

An innovative, facile, low- cost and one-pot hydrothermal synthesis was developed for preparing a high fluorescence carbon dots (CDs). In this report for the first time, Lawsonia inermis (Henna) plant as a carbon source was used to produce CDs without adding any chemical reagent and it was characterized by different techniques. The as-synthesized CDs exhibit high stability under various conditions and exceptionally solubility in hydrophilic solvents such as water and ethanol. In addition, the CDs were employed as a biocompatible probe for determination of methotrexate (MTX) in the range of 0.02 µmol L-1 to 18 µmol L-1 with a detection limit as 7 nmol L-1. Highly selective and sensitive determination of MTX was carried out through the fluorescence resonance energy transfer (FRET) mechanism. It is noteworthy that, the antibacterial studies of this CDs lead to interesting results which suggested Henna CDs kill Gram-positive and Gram-negative bacteria like an antibiotic drug. Also, compared with the henna plant, CDs show antibacterial properties in much lower concentrations.

Artemisinin can inhibit the calmodulin-mediated activation of phosphodiesterase in comparison with Cyclosporin A.

Artemisinin and Cyclosporin A were examined for their ability to inhibit the calmodulin-mediated activation of phosphodiesterase, which is based on the hydrolysis of cAMP to AMP by phosphodiesterase in the presence or absence of inhibitors, followed by quantitative analysis using spectrophotometer method. Anti-calmodulin activity of these agents was investigated by spectrofluorometry. Our results indicates that Artemisinin and Cyclosporin A induced some conformational changes on calmodulin and increased the fluorescence emission, but Artemisinin increased fluorescence emission of calmodulin in higher amounts compared with the Cyclosporin A. Kinetic analysis of the Artemisinin-calmodulin and Cyclosporine A-calmodulin interaction showed that these agents competitively inhibited the activation of phosphodiesterase without affecting Vmax. Artemisinin increased Km value in higher amounts compared with the Cyclosporin A. Ki values of Artemisinin and Cyclosporin A were determined as 10 microM and 35 microM, respectively. The DeltaG (H2O), the best parameter for the estimation of macromolecule stability, was determined for calmodulin in the absence and presence of Artemisinin and Cyclosporin A. However, the degree of decrease in DeltaG (H2O) value was as follows: Artemisinin>Cyclosporin A, which means Artemisinin induced more instability in the calmodulin structure.In conclusion, our findings showed a good correlation between the ability of both Artemisinin and Cyclosporin A to block the activation of phosphodiesterase and their ability to bind to the activator and that Artemisinin is a more potent inhibitor of phosphodiesterase compared with Cyclosporin A.

Flow-injection chemiluminescence determination of enrofloxacin using the Ru(phen)3(2+)-Ce(IV) system and central composite design for the optimization of chemical variables.

The main purpose of this study was to develop an inexpensive, simple, rapid and sensitive chemiluminescence (CL) method for the determination of enrofloxacin (ENRO) using a flow-injection system. This method is based on rapid reduction of Ru(phen)(3)(3+), which is produced in the reaction between Ru(phen)(3)(2+) and acidic Ce(IV) by ENRO, producing strong CL. A central composite design (CCD) was used for optimization of the chemical variables. Regression analysis of the data from the CCD demonstrated that a second-order polynomial model is an adequate description of the surface over the factor limits studied. Optimization using CCD gave approximately four-fold better results than the single-factor-at-a-time method. Under optimal experimental conditions, the CL response was proportional to the concentration of ENRO over a wide range (0.008-3.6 microg/mL) with a correlation coefficient of 0.9986 and a detection limit of 0.003 microg/mL (3sigma). The relative standard deviation for 11 repeated determinations of 0.14 microg/mL ENRO was 4.2%. This method was successfully applied to the analysis of commercial formulations, spiked plasma and spiked poultry tissue. Sample analyses showed good recovery percentages for drugs and spiked plasma (95.1-103.9%). Recovery percentages for spiked poultry tissue were in the range 77.6-87.3%. The minimum sampling rate was 100 samples/h.