Change In Dielectric Constant Research Articles

New Opportunities Offered By Lipid-Modified Electrodes to Interrogate Transmembrane Diffusion Mechanisms and Kinetics

Diffusion of small molecules between intra- and extra-cellular spaces across lipid layers is instrumental to the understanding of fundamental biological transport processes and the improvement in drug delivery schemes. In natural systems, organisms develop intricate ion channels and stimuli-responsive gating machineries for signal transduction, cell identification, and toxin removal, while still allowing the selective and proficient uptake of vital nutrients that are critical to survival, growth, and reproduction. Understanding membrane function is a colossal step in developing cutting-edge drug therapies in a rational way. Lipinski’s rule of five describes the molecular properties essential for the bioavailability and pharmacokinetics of candidate drugs inside human bodies and thus serves as a first-order consideration for drug design.Altering the length of an alkyl tail is thus a viable method to tune the lipophilicity of a compound, thus modulating the transport properties of the drug. In this presentation, we report on our efforts to interrogate the “flip-flop” diffusion mechanism of alkyl proton carriers traversing the lipid layer of a hybrid bilayer membrane (HBM) using electrochemical techniques including but not limited to electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and pulse techniques. The 4-nm thick HBM electrochemical platform consists of a lipid monolayer appended on top of a self-assembled monolayer (SAM) containing a dinuclear Cu-triazole complex for O2 reduction reaction (ORR) on a Au electrode prepared using electron-beam evaporation (Scheme 1a). The “flip-flop” diffusion rates of the proton carriers dictate the O2 reduction turnover frequency by the Cu-based electrocatalyst. By varying both the tail lengths of the proton carriers and the lipids, we find that a difference between the lipid tail lengths and the proton carrier tail lengths of approximately 6-10 Å results in a maximum “flip-flop” diffusion rate. We evaluate these empirical findings using a biophysical model that contains parameters considering changes in Coulombic interactions, stress buildup, surface tension, and dielectric constants across the lipid-water interface. The model correctly mimics the relative alterations in the energy barriers associated with the rate-determining step (RDS) for the “flip-flop” diffusion process (Scheme 1b). Studies with a rigid proton carrier further substantiate findings that the RDS involves the bending of the alkyl tail of the proton carrier as it moves across the hydrophobic interior of the lipid layer. We envision that the methodologies developed here will ultimately lead to improved understanding of the mechanismof “flip-flop” diffusion in lipid bilayers and aid in the development of next-generation targeted drug delivery schemes. Acknowledgements. E.C.M.T. acknowledges a Croucher Foundation Scholarship. We thank the US Department of Energy (DE-FG02-95ER46260) for support of this research. Scheme 1 is presented here. Figure 1

A modified structure for MOSFET-like carbon nanotube FET

In this paper, non-equilibrium Green’s function method is used to investigate the characteristics of carbon nanotube field-effect transistors (CNTFETs). Leakage current resulted from band-to-band tunneling, and ambipolarity behaviors are among the known effects for CNTFET devices. To minimize these phenomena, a modified structure is presented in which density of source and drain in the transistor is reduced in steps while going toward the intrinsic channel. The proposed structure shows a better ambipolar property and less power-delay product at a given I ON/I OFF ratio, and also less delay time at a given I ON compared with the available structure. Also, its other ON- and OFF-state characteristics are almost intact. Afterward, the effect of different factors on the behavior of the device and their optimal values such as channel length changes, chirality, dielectric constant, and gate length changes are investigated.

Properties of silver phosphate glass in the presence of nanosize cobalt and nickel oxides

Silver phosphate glasses, undoped and doped with 0, 5, 10, 15 & 20wt.% CoO/NiO were prepared by quench melt technique. The prepared glasses were characterized by using X-ray diffraction and FTIR spectroscopic techniques. Glass transition temperatures were determined by Differential Scanning Calorimetric technique whereas morphological changes in the freshly prepared and aged glasses were examined by SEM technique. Electrical conductivities and dielectric constants of all the glasses were measured at different temperatures and frequencies. Structural changes and changes in electrical conductivities and dielectric constants with temperature and frequencies have been discussed and a plausible mechanism is given.

Surface plasmon resonance sensor using functionalized alkanethiols monolayer for illegal compound detection

The development of highly sensitive detection of [Formula: see text]-agonists compound by using surface plasmon resonance (SPR) immunoassay functionalized alkanethiols monolayer on gold surface was reported here. For the construction of robust SPR sensor surface, the illegal compound (as antigen) was immobilized onto gold succinimide-terminated monolayer to perform amide-coupling reaction. Structural characteristic of monolayer is an important issue for further application of selt-assembled monolayer (SAM)-based molecular electronics. This study focuses on the relation between structure of alkanethiols SAM of different chain length and its sensitivity of the detection. The surface structure is characterized by electrochemical methods and STM. The target compound in this research is clenbuterol as farmers used illegally to increase their profit gain. For the detection of clenbuterol, indirect competitive inhibition method was used. In this work, the SPR senses the dielectric constant change at the interface from the binding of the unreacted antibody to antigen-immobilized on the sensor surface. By this method, clenbuterol can be detected within ppt level and only requires 5[Formula: see text]min per sample. Furthermore, shorter chain alkanethiol sensor surface produces higher sensitivity in the detection process.

Photoinduced Electron Transfer Elicits a Change in the Static Dielectric Constant of a de Novo Designed Protein.

We provide a direct measure of the change in effective dielectric constant (ε(S)) within a protein matrix after a photoinduced electron transfer (ET) reaction. A linked donor-bridge-acceptor molecule, PZn-Ph-NDI, consisting of a (porphinato)Zn donor (PZn), a phenyl bridge (Ph), and a naphthalene diimide acceptor (NDI), is shown to be a "meter" to indicate protein dielectric environment. We calibrated PZn-Ph-NDI ET dynamics as a function of solvent dielectric, and computationally de novo designed a protein SCPZnI3 to bind PZn-Ph-NDI in its interior. Mapping the protein ET dynamics onto the calibrated ET catalogue shows that SCPZnI3 undergoes a switch in the effective dielectric constant following photoinduced ET, from ε(S) ≈ 8 to ε(S) ≈ 3.

Electromagnetic field properties influence by the changes of dielectric material constant

This paper deals with of input parameters observation of the electromagnetic field generator. The frequency course character of this parameter plays a key role in specific sensor kind sensing principle. This senor is designed for non-electrical quantities measurement. The sensing principle is based on changes of electromagnetic field properties which are affected by this sensor resonance. This paper contains complete design of this sensor with analytical model, which describe sensing principle. The second part of this paper is focused to detail numerical analysis by new multi-numerical calculation techniques. Result of this analysis describe not only the sensor functionality but also change of sensor characteristic when is used structural material with another dielectric parameters. Streszczenie. Artykul dotyczy analizy parametrow wejściowych generatora pola elektromagnetycznego. Charakterystyki czestotliwościowe tych parametrow odgrywają kluczową role w zastosowaniu specyficznego czujnika. Czujnik ten zostal zaprojektowany do pomiaru wielkości nieelektrycznych. Zasada dzialania bazuje na zmianach wlaściwości pola elektromagnetycznego przy zmianach czestotliwości rezonansowej czujnika. Artykul opisuje caly proces projektowania czujnika lącznie z modelem analitycznym opisującym zasade dzialania. Druga cześc artykulu skupia sie na analizie numerycznej wykorzystującej hybrydowe metody obliczeniowe. Wyniki analizy pokazują zastosowanie czujnika wykonanego z roznych materialow o roznych parametrach dielektrycznych. (Zmiany wlaściwości pola elektromagnetycznego w zalezności od stalej dielektrycznej materialu).

Magnetocapacitance effect in ferromagnetic LiNbO3 nanoparticles

Magnetocapacitance and magnetization behavior as a function of reduction heat treatment at 650°C and 900°C in a 5%H2–Ar atmosphere on LiNbO3 nanocrystalline are reported. There is a change of intrinsic dielectric constant (κ) from 822 to 860 produced by spin polarization using an external magnetic field. The Raman, X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy, indicate vibration mode changes localized at Nb–O bonds in the octahedron NbO6, shifts in the binding energy of the electronic structure of ions of niobium (3d) and the oxygen (1s). It is due to the oxygen vacancies caused by reduction heat treatment process. Moreover there is ions redistribution of Nb+3, Nb+4and Nb+5 at the surface of the nanoparticles.

Membrane Lateral Pressure Controls Hydration and Water Mobility at the Copper-Binding Site of the P1B-type Copper ATPase CopA from Legionella Pneumophila

P-type ATPases couple ATP hydrolysis to ion transport. We have reconstituted the copper-transporting P1B-type ATPase LpCopA from Legionella pneumophila into lipid nanodiscs in order to study the influence of membrane lateral pressure on the functionally relevant intra-membrane protein hydration at the ion-binding site. Using site-directed mutagenesis, the solvatochromic fluorophore BADAN was covalently linked to the cysteine residues at the conserved copper-binding CPC motif on transmembrane helix 4. The decomposition of the fluorescence spectra of labeled LpCopA in the micellar and the lipid-inserted state shows that membrane lateral pressure reduces hydration and water mobility in the environment of the more buried Cys-382 with a concomitant change of the local dielectric constant by −9. In contrast, the environment of Cys-384 which is located closer to the putative membrane surface, resembles a “hydrophobic gate” with low water mobility that is little affected by insertion into a bilayer (change of local dielectric constant by −3). The asymmetric hydration and water mobility around the CPC motif provides Cys-382 with a highly dynamic hydration. The data show that membrane lateral pressure may provide a restoring force in hydration / dehydration cycles around Cys-382 in the transmembrane domain during catalytic activity. The lower hydration and mobility in the Cys-384 environment, on the other hand, would favor the dehydration of copper and hinder its re-solvation from the intracellular side.

Modeling Bare Soil L-Band Polarimetric - Values Using a Second-Order SPM Model

Polarimetric soil moisture retrieval is among the main objectives of leading synthetic-aperture-radar satellite missions since it allows to systematically analyze costly-to-obtain polarization information to increase retrieval accuracy. In this letter, we present the results of modeling the L-band entropy $(H)$ and alpha $(\alpha)$ values as a function of soil dielectric constant and roughness using a second-order small-perturbation model to simulate the polarimetric soil backscattering. Modeling results are then compared to bare soil uninhabited aerial vehicle synthetic aperture radar (UAVSAR) data acquired simultaneously to in situ field campaigns in Canada during SMAPVEx12. Our model is able to correctly predict observed ranges of $H$ and $\alpha$ and to consistently model dielectric constant and roughness changes. Nevertheless, a systematic overestimation of $\alpha$ is observed when compared with the analyzed UAVSAR data set. Taking UAVSAR data as benchmark, theoretical reasons for this mismatch are analyzed.

Molecular dynamics simulations of the electric double layer capacitance of graphene electrodes in mono-valent aqueous electrolytes

Electrical double layer (EDL) capacitors based on recently emergent graphene materials have shown several folds performance improvement compared to conventional porous carbon materials, driving a wave of technology breakthrough in portable and renewable energy storage. Accordingly, much interest has been generated to pursue a comprehensive understanding of the fundamental yet elusive double layer structure at the electrode/electrolyte interface. In this paper, we carried out comprehensive molecular dynamics simulations to obtain a comprehensive picture of how ion type, solvent properties, and charging conditions affect the EDL structure at the graphene electrode surface, and thereby its contribution to capacitance. We show that different symmetrical monovalent aqueous electrolytes M+X– (M+ = Na+, K+, Rb+, and Cs+; X– = F–, Cl–, and I–) indeed have distinctive EDL structures. Larger ions, such as, Rb+, Cs+, Cl–, and I–, undergo partial dehydration and penetrate through the first water layer next to the graphene electrode surfaces under charging. As such, the electrical potential distribution through the EDL strongly depends on the ion type. Interestingly, we further reveal that the water can play a critical role in determining the capacitance value. The change of dielectric constant of water in different electrolytes largely cancels out the variance in electric potential drop across the EDL of different ion type. Our simulation sheds new lights on how the interplay between solvent molecules and EDL structure cooperatively contributes to capacitance, which agrees with our experimental results well.

Distribution of THz electric field in the split-ring resonator metamaterials based on the thin film geometry

We investigate THz response of split-ring resonator prepared on the polyimide film grown on the Si substrate. We observe a strong thickness dependence of the resonance frequency which is attributed to the change in the effective dielectric constant. From the finite-difference time-domain simulation, we reproduce experimental results, and find large variations of the electric field profile depending on the polyimide thickness. We discuss the optimal film configuration to achieve the large enhancement of THz electric field which depends strongly on thicknesses and optical constants of constituent layers.

Metal Nanostructures Fabricated by the Difference of Interfacial Energy at a Dielectric/Metal Interface

Abstract Due to its high sensitivity to changes in the environmental dielectric constant, localized surface plasmon resonance (LSPR) is utilized for various sensing materials. However, because of this high sensitivity, it is difficult to detect a specific substance among mixed materials. Here, we enhanced the size selectivity using a metal nanostructure. By preparing a cup-like metal nanostructure that is the same size as a virus, this cup-like structure may be able to capture a virus, and thus the LSPR characteristics would change. This phenomenon would not occur for larger materials, such as animal cells, i.e., this cup-like structure may have selectivity for material size. In this paper, we fabricated metal nanocups out of two-dimensional colloidal crystals by exploiting the difference of interfacial energy at a dielectric/metal interface. The size selectivity and plasmon characteristics of the fabricated metal nanocups were investigated with model viruses, i.e., virus-like polystyrene (PSt) nanoparticles with almost the same dielectric constant and size as a virus. As a result, the transmission spectra show a 20-nm red shift in the visible light range before and after adsorption of the model virus. Field emission scanning electron microscopy (FE-SEM), optical microscopy, UV–vis spectrometry and contact angle measurement results are also discussed.

Large low field room temperature magneto-dielectric response from (Sr0.5Ba0.5)Nb2O6/Co(Cr0.4Fe1.6)O4 bulk 3-0 composites

Abstract Bulk magneto-dielectric composites with a 3-0 configuration comprised of ferroelectric-magnetostrictive phases have been synthesized using (Sr0.5Ba0.5)Nb2O6–Co(Cr0.4Fe1.6)O4 as the two constituents, respectively. The ferroelectric phase made by a dual stage sintering process has a uniform grain size of 15 μm while the magnetostrictive phase has a grain size of 2–3 μm. Composites synthesized by conventional solid state processing using these two constituents exhibit large magneto-dielectric coupling at room temperature which increases with increasing magnetic field. The composite with 30% magnetostrictive phase distributed uniformly in the ferroelectric phase has the most desirable microstructure and exhibits a large coupling with 3.2% change in the dielectric constant at 1 kHz and 8 kOe magnetic field. This change in dielectric constant was found to be a maximum with respect to variation of the fraction of magnetostrictive phase, indicating that 30% is the optimal value to realize large coupling between the two phases. The decrease in magneto-dielectric constant upon application of an external magnetic field is possibly due to the inherent magnetoresistance of the magnetic component. The resistivity of the magnetic component decreases in an external magnetic field leading to the formation of 3D percolating conducting paths. This causes the coupling to decrease in composites with >30% magnetostrictive phase.

Influence of the Compatible Solute Ectoine on the Local Water Structure: Implications for the Binding of the Protein G5P to DNA.

Microorganisms accumulate molar concentrations of compatible solutes like ectoine to prevent proteins from denaturation. Direct structural or spectroscopic information on the mechanism and about the hydration shell around ectoine are scarce. We combined surface plasmon resonance (SPR), confocal Raman spectroscopy, molecular dynamics simulations, and density functional theory (DFT) calculations to study the local hydration shell around ectoine and its influence on the binding of a gene-5-protein (G5P) to a single-stranded DNA (dT25). Due to the very high hygroscopicity of ectoine, it was possible to analyze the highly stable hydration shell by confocal Raman spectroscopy. Corresponding molecular dynamics simulation results revealed a significant change of the water dielectric constant in the presence of a high molar ectoine concentration as compared to pure water. The SPR data showed that the amount of protein bound to DNA decreases in the presence of ectoine, and hence, the protein-DNA dissociation constant increases in a concentration-dependent manner. Concomitantly, the Raman spectra in terms of the amide I region revealed large changes in the protein secondary structure. Our results indicate that ectoine strongly affects the molecular recognition between the protein and the oligonucleotide, which has important consequences for osmotic regulation mechanisms.

Fiber optic hydrogen gas sensor utilizing surface plasmon resonance and native defects of zinc oxide by palladium

We present an experimental study on a surface plasmon resonance (SPR) based fiber optic hydrogen gas sensor employing a palladium doped zinc oxide nanocomposite (ZnO(1−x)Pdx, 0 ≤ x ≤ 0.85) layer over the silver coated unclad core of the fiber. Palladium doped zinc oxide nanocomposites (ZnO(1−x)Pdx) are prepared by a chemical route for different composition ratios and their structural, morphological and hydrogen sensing properties are investigated experimentally. The sensing principle involves the absorption of hydrogen gas by ZnO(1−x)Pdx, altering its dielectric function. The change in the dielectric constant is analyzed in terms of the red shift of the resonance wavelength in the visible region of the electromagnetic spectrum. To check the sensing capability of sensing probes fabricated with varying composition ratio (x) of nanocomposite, the SPR curves are recorded typically for 0% H2 and 4% H2 in N2 atmosphere for each fabricated probe. On changing the concentration of hydrogen gas from 0% to 4%, the red shift in the SPR spectrum confirms the change in dielectric constant of ZnO(1−x)Pdx on exposure to hydrogen gas. It is noted that the shift in the SPR spectrum increases monotonically up to a certain fraction of Pd in zinc oxide, beyond which it starts decreasing. SEM images and the photoluminescence (PL) spectra reveal that Pd dopant atoms substitutionally incorporated into the ZnO lattice profoundly affect its defect levels; this is responsible for the optimal composition of ZnO(1−x)Pdx to sense the hydrogen gas. The sensor is highly selective to hydrogen gas and possesses high sensitivity. Since optical fiber sensing technology is employed along with the SPR technique, the present sensor is capable of remote sensing and online monitoring of hydrogen gas.

Sensitivity Modeling of an RFID-Based Strain-Sensing Antenna With Dielectric Constant Change

An radiofrequency identification (RFID)-based folded patch antenna has been developed as a novel passive wireless sensor to measure surface strain and crack, for the structural health monitoring of metallic structures. Up to 2.5 m of read range is achieved by a proof-of-concept prototype patch antenna sensor with a strain sensitivity around −760 Hz/ $\mu \varepsilon $ , which is equivalent to a normalized strain sensitivity of −0.74 ppm/ $\mu \varepsilon $ . In this paper, we propose to consider the change of the substrate dielectric constant due to strain when modeling the antenna sensor. An enhanced strain sensitivity model is introduced for more accurately estimating the strain sensing performance of the hereby introduced smart skin antenna sensor. Laboratory experiments are carried out to quantify the dielectric constant change under strain. The measurement results are incorporated into a mechanics–electromagnetics coupled simulation model. Accuracy of the multi-physics coupled simulation is improved by integrating dielectric constant change in the model.

Tailoring the Field Distribution of ZnO by Polyaniline for SPR-Based Fiber Optic Detection of Hardness of the Drinking Water

Due to the industrial development, drinking water is getting polluted by disposing several waste products of the industries. Hardness is one of the prominent impurities in drinking water which is mainly due to the presence of carbonate and bicarbonate ions (CO3 2− and HCO3 −) in it. Here, we present the synthesis of the zinc oxide (ZnO) and polyaniline (PANI) nanocomposite for the detection and estimation of hardness of the drinking water. The chemical formula of such a nanocomposite is defined in terms of the fraction of polyaniline nanoparticles reinforced in ZnO matrix and is derived as ZnO(1 − x)PANI x (0 ≤ x ≤ 0.9); x is the composition ratio. Silver and ZnO(1 − x)PANI x layers are coated over the unclad core of the optical fiber so as to create the four layer system as that of Kretschmann configuration SPR structure. The working principle involves the change in dielectric constant of (ZnO(1 − x)PANI x ) by CO3 2− or HCO3 − ions in aqueous atmosphere. Due to the strong interaction of the sensing surface to the CO3 2− and HCO3 − ions, a red shift in the SPR spectrum is observed in the concentration range 0–200 μg/l. The sensitivity of the sensor depends on the composition ratio of the nanocomposite and has been found to be maximum for the composition ratio lying in the range 0.45–0.60. This has been further confirmed in terms of the enhancement of the electric field density and found to be in agreement with the experimental value. The sensitivity of the sensor with optimum value of the composition ratio is 0.094 and 0.065 nm/(μg/l) for CO3 2− and HCO3 −, respectively. The sensor is highly selective to CO3 2− and HCO3 −. The sensor has advantages of online monitoring and remote sensing of water quality because the probe is fabricated over an optical fiber.

Direct observation of magnetodielectric effect in type-I multiferroic PbFe0.5Ti0.25W0.25O3

In type-I multiferroics, where ferroelectricity and magnetism arise from different origins, the explicit measurement of magnetoelectric effect is commonly prohibited due to the weak magnetoelectric coupling. From our investigation of magnetic and dielectric properties in a perovskite PbFe0.5Ti0.25W0.25O3, we have directly demonstrated magnetic-field-driven change of dielectric constant in a highly non-linear fashion. Our result offers a potential utilization of magnetoelectric functionality in type-I multiferroics.

Electrical detection of ortho-para conversion in fullerene-encapsulated water.

Water exists in two spin isomers, ortho and para, that have different nuclear spin states. In bulk water, rapid proton exchange and hindered molecular rotation obscure the direct observation of two spin isomers. The supramolecular endofullerene H2O@C60 provides freely rotating, isolated water molecules even at cryogenic temperatures. Here we show that the bulk dielectric constant of this substance depends on the ortho/para ratio, and changes slowly in time after a sudden temperature jump, due to nuclear spin conversion. The attribution of the effect to ortho–para conversion is validated by comparison with nuclear magnetic resonance and quantum theory. The change in dielectric constant is consistent with an electric dipole moment of 0.51±0.05 Debye for an encapsulated water molecule, indicating the partial shielding of the water dipole by the encapsulating cage. The dependence of bulk dielectric constant on nuclear spin isomer composition appears to be a previously unreported physical phenomenon.

Evaluation of theophylline imprinted polypyrrole film

In this study some affinity and dielectric properties of molecularly imprinted (MIP) conducting polymer—polypyrrole (Ppy) based thin films were evaluated. Films of polypyrrole molecularly imprinted with theophylline (MIP–Ppy) and non-imprinted polypyrrole (NIP–Ppy) were formed on boron doped silicon (Si) substrates in order to evaluate the efficiency of Ppy to bind theophylline. The substrates were modified with boron-doped oxygen terminated nanocrystalline diamond (B:NCD:O) The dielectric properties of B:NCD:O/Ppy-based multi-layered structures were analyzed using spectroscopic ellipsometry and spectrophotometric techniques. Electrochemical impedance spectroscopy was applied for the investigation of kinetics of theophylline interaction with MIP–Ppy and NIP–Ppy. The sensitivity of molecularly imprinted and non-imprinted polymer films was analyzed by injection of different theophylline concentrations. Assuming that Ppy film electrical capacitance change is a result of Ppy dielectric constant change induced by absorbed theophylline molecules, the electrical capacitance change (ΔC) kinetics at different concentrations of theophylline was analyzed using first pseudo order kinetic equation. The dissociation equilibrium constant KD of MIP–Ppy/theophylline complex at room temperature was calculated as 1.7×10−8M, and Gibbs free energy change (ΔG) of MIP–Ppy/theophylline complex formation was calculated as −43.5kJ/mol. It was concluded that molecularly imprinted polypyrrole thin film could be used for the detection of theophylline.