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Electrochemical biosensors based on structure‐switching aptamers offer many advantages because they can operate directly in complex samples and offer the potential to integrate with miniaturized electronics. Unfortunately, these biosensors often suffer from cross‐reactivity problems when measuring a target in samples containing other chemically similar molecules, such as precursors or metabolites. While some progress has been made in selecting highly specific aptamers, the discovery of these reagents remains slow and costly. In this work, a novel strategy is demonstrated to distinguish molecules with miniscule difference in chemical composition (such as a single hydroxyl group)—with cross reactive aptamer probes—by tuning the charge state of the surface on which the aptamer probes are immobilized. As an exemplar, it is shown that the strategy can distinguish between DOX and many structurally similar analytes, including its primary metabolite doxorubicinol (DOXol). Then the ability to accurately quantify mixtures of these two molecules based on their differential response to sensors with different surface‐charge properties is demonstrated. It is believed that this methodology is general and can be extended to a broad range of applications. [ABSTRACT FROM AUTHOR]

In this study, a downsized direct current (dc)-gas-insulated transmission line (GIL) model is applied to investigate the surface charging and discharging characteristics of the basin-type spacer in 0.1-MPa SF6 and air. Under a low electric field, the surface charge accumulation is dominated by the bulk conduction of the spacer. As the charging voltage increases, gas ionization occurs in the localized strong electric field, taking over the dominant position. In 0.1-MPa SF6 gas, flashovers typically develop along the convex surface of the spacer under both positive and negative voltages because the homo-charge accumulation induced by brush discharges on the concave surface aggravates the electric field distortion at the convex side. In air, the dc flashovers have the polarity effect. Under the negative voltage, the flashover development is similar to that in SF6 gas. But for positive polarity, the space charge region of positive polarity intensifies the electric field ahead of the corona region, thus promoting the air-gap breakdown at the concave side of the spacer. [ABSTRACT FROM AUTHOR]

Free metal particle can affect surface charge accumulation on epoxy insulator installed in gas-insulated transmission line (GIL) or gas-insulated switchgear (GIS), which results in reduction of surface flashover voltage thus threatening the safe operation of the power equipment. This article reports on the charge accumulation behavior on a real size epoxy insulator with bouncing metal particle under DC voltage. A coaxial electrode system was designed for the test under −30 kV, a metal particle-launching system was employed to inject the bouncing linear particle to the insulator surface. The charge distribution was measured by a Kelvin-type probe, and the influence of the particle on the charge accumulation was analyzed with the help of electric field simulation. The results showed that there were mainly two moving patterns of the bouncing particle: the charges were accumulated with speckle shape and the charged particle that hit the edge of electrode had more remarkable influence on the charge accumulation than other particles. It is suggested that the charge distribution feature is dependent upon the collision point and the trajectory of the bouncing particle. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on epoxy insulator installed in gas-insulated transmission line (GIL) and gas-insulated switchgear (GIS) has been recognized as a crucial factor for electric field distortion that results in the reduction of surface flashover voltage. This article reports on the gaseous ionization dependence of the charge accumulation pattern on a real-size epoxy insulator with multiarc surface profile by using various gas atmospheres. A coaxial electrode system was designed to investigate the charging behavior under dc voltages of −10, −20, and −30 kV. The insulator and electrodes were placed in a metal-enclosed test chamber, which was filled with 0.1 MPa air or 0.4 MPa SF6/N2 mixture to estimate the influence of the gas atmosphere on the charge accumulation behavior by a Kelvin-type probe. The accumulation mechanism and the electric field distortion induced by the charges were demonstrated based on numerical simulation. The results indicated that positive charges were accumulated in the shape of speckle on insulator surface in air, whereas both positive and negative charges were accumulated in SF6/N2 mixture and positive charge speckles appeared in SF6/N2 mixture only when the voltage raised up to −30 kV. It is considered that the charge accumulation behavior is determined by the competition result among the bulk, the gas and the surface conductions. As compared with the case in air, gaseous ionization in SF6/N2 mixture is more difficult to occur, which leads to the obvious difference in the charge accumulation pattern. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on epoxy insulator installed in gas insulated switchgear (GIS) or gas insulated transmission line (GIL) has been recognized as an important factor for electric field distortion that results in reduction of surface flashover voltage. This paper reports on surface charge accumulation behavior on a actual epoxy insulator for 100 kV GIL prototype with multi-arc surface profile. A coaxial electrode system is used to investigate the charging behavior under DC voltages with metal particles positioned at various positions of the surface so as to estimate its influence on the charge accumulation behavior using a Kelvin type probe. The results show that positive charges are accumulated mainly on the nonplanar region around the high voltage electrode in the shape of speckles, and the average charge distribution along the radial direction presented a double-peak feature. Moreover, the charge accumulation is enhanced by metal particles contacting to the grounded electrode. Using a numerical simulation method, it is suggested that the charge accumulation is mainly determined by gaseous ionization which is enhanced by the metal particle induced electric field distortion. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on polymer insulating material has been recognized as an important factor for electric field distortion that results in reduction of surface flashover voltage. This paper reports on the charge accumulation behavior between a pair of finger-shaped electrodes on epoxy/Al2O3 nanocomposites under dc voltage superimposed by repetitive pulses. The charge distribution was measured by means of an electrostatic voltmeter, from which the average charge density could be calculated. Effects of dc voltage, nanofiller content, and pulse voltage on charge accumulation behavior were investigated. Obtained results showed that with the increase in the filler content from 0 wt% to 5 wt%, the average charge density increased initially then appeared to decrease. The superposition of repetitive pulses on dc voltage led to a remarkable growth in charge accumulation as compared with that when only dc voltage was applied. It is suggested that the charges are originated from local gaseous ionization and/or electrode injection, which is determined by the combined voltage. The charge density is dependent upon the surface trap, which is affected by nanofiller content. The superposition of repetitive pulse is considered as a possible reason to encourage local gaseous ionization that results in enhanced accumulation of surface charge. [ABSTRACT FROM AUTHOR]

Charge generation at the interfaces of gas-insulated switchgear or gas-insulated lines is mostly studied from a macroscopic point of view. Integral current measurements are a common method to determine the average inception field strengths and intensities of micro discharges. However, because of the lack of spatial resolution and measurement sensitivity, these experiments do not provide deeper insights on the microscopic processes. By applying surface potential measurement techniques, studying the charge generation of single interface protrusions and drawing conclusions relative to their spatial distribution have become possible. This paper presents a spatially resolved analysis of charge-generation processes at rough aluminum electrodes and insulating interfaces. The results reveal a highly inhomogeneous charge generation at the interfaces even for electric fields below 6 kV/mm. Analyzing the charge generation from a macroscopic perspective has been demonstrated to possibly underestimate the local charge generation by up to three orders of magnitude. Using sulfur hexafluoride (SF6) as the insulation gas at 0.45 MPa and Al2O3-filled epoxy resin insulators, the inception field strength for charge generation at the insulating interface is measured to be 3 kV/mm. For a technical insulation system that includes both a rough aluminum electrode and an insulating interface, significant discharge intensities are observed at a 5-kV/mm electric field. From these results, micro discharges are expected to be highly relevant for dimensioning of gas-insulated devices. [ABSTRACT FROM AUTHOR]

Surface charge accumulation of polymer insulating materials is harmful to the safe operation of electrical equipment, especially under DC electric field excitation. In order to ensure the safety and stable operation of HVDC power system such as Gas-insulated transmission line, it is necessary to understand the influence of the surface charge on the flashover and improve the surface charge dynamic characteristics. In this paper, Epoxy resin (EP) is deposited by SiOx thin films with different plasma treatment conditions. The flashover voltages are measured with and without surface charges. The results show that the flashover occurs at lower voltage due to the accumulated charges on the EP surface. In particular, the surface charge with the same polarity of flashover discharge can reduce the surface flashover voltage significantly. Moreover, the charge decay rate is increased up to 90% by plasma treatment of 3 min, corresponding flashover voltage is increased. In addition, the flashover voltages of samples during the surface charge dissipation are obtained. Both static impact index I and dynamic impact index S are introduced to estimate effect of surface charge on dielectric surface flashover. [ABSTRACT FROM AUTHOR]

The established theories behind low-field ion-drift currents assume that the charge generation from natural ionization is the main source of the charge-carriers, and that it defines the current flowing through the insulation gas in gas-insulated direct current (DC) devices. This charge generation is assumed to be independent of the applied electric field in the cases where the electric field is sufficiently below the onset of microdischarges at the interfaces. However, the results of a few previous studies have suggested the presence of a field-dependent current contribution from some conduction processes, which might significantly accelerate the decay of the surface charges distributed on the insulator surfaces. In this paper, an extensive study on low-field charge transport is presented, and the influences of the insulation volume, electric field, and gas pressure on low-field charge transport are discussed. In accordance with the common structure employed in gas-insulated devices, Al2O3-filled epoxy resin is used in the solid parts of the device and sulfur hexafluoride (SF6) is used for gaseous insulation. At electric fields of approximately 1800 V/m, a gas current that is up to 30 times higher, when compared to the conduction currents caused by the charge generation from natural ionization, is observed. This enhanced current reveals a further conduction process acting in a limited range of low electric fields and is characterized to be independent of the applied voltage polarity. With an increase in the gas pressure, the current amplitude is found to increase linearly and higher electric field is required to reach its maximum. At electric fields below 200 V/m, the conduction current reverses its pressure dependency and increases with decreasing gas pressure. The reported findings strongly indicate that the enhanced low-field charge transport in gasinsulated devices may be owing to electrophoretic conduction. [ABSTRACT FROM AUTHOR]

Tailoring Electrode Surface Charge to Achieve Discrimination and Quantification of Chemically Similar Small Molecules with Electrochemical Aptamers (Adv. Funct. Cross-reactivity, drug discrimination, drug quantification, electrochemical aptamer biosensors, nanostructured electrodes, surface charge Keywords: cross-reactivity; drug discrimination; drug quantification; electrochemical aptamer biosensors; nanostructured electrodes; surface charge EN cross-reactivity drug discrimination drug quantification electrochemical aptamer biosensors nanostructured electrodes surface charge 1 1 1 01/05/23 20230103 NES 230103 B Electrochemical Aptamer Biosensors b In article number 2208534, Fu, Soh, and co-workers report an electrochemical biosensor to distinguish molecules with a minuscule difference in chemical composition by tuning the charge state of the surface on which the aptamer probes are immobilized. [Extracted from the article]

Silicone rubber (SiR), as a basic insulating material, is widely used in insulators for HVDC transmission lines. The prominent characteristics of the SiR coating are the hydrophobicity and the hydrophobicity recovery, which can suppress the development of leakage currents and dry-band discharges, and prevent the flashover incidents. Fluorination is a method to change the chemical component of the surface layer of polymers, which could induce the corresponding change in hydrophobicity and some electrical properties, thus influencing the dc surface flashover characteristics. Room temperature vulcanized (RTV) SiR samples were fluorinated in a stainless reaction vessel at about 298K (25°C) using a F2/N2 mixture with 12% F2 by volume and 0.05 MPa (500 mbar) for respectively 5, 10, 15 and 20 minutes. The hydrophobicity of samples with different fluorination time was measured by the static contact angle tests after corona aging. The variation of hydrophobicity with the lapse of time was recorded. Dc flashover tests in different conditions were carried out between two plane electrodes on top of the material sample. The flashover voltage was found to be associated with the surface hydrophobicity status of samples. Obtained results showed the effects of the fluorination on the surface charge, hydrophobicity performance and dc flashover voltage. It is suggested that the appropriate fluorination can improve surface hydrophobicity and suppress surface charge accumulation, thus raising the dc flashover voltage. [ABSTRACT FROM AUTHOR]

Epoxy is widely used in electronic and electrical devices because of its excellent insulation properties. The addition of nanoparticles to epoxy could change the material structure and then charge behaviors are altered as a consequence. The accumulation of surface charge may cause electric field distortion, which would lead to surface flashover. In this paper, the samples were made by dispersing nano-scale boron nitride (BN) particles in Epoxy with the weight ratios of 5, 10, 20, 30, 40 wt%. The samples were charged by a dc corona triode system using needle-plate electrodes. The distribution of charges was measured with an electrostatic voltmeter and the effect of nanoparticles on charge accumulation and decay behavior was studied. A flashover test was carried out under a dc stress between two finger-type electrodes. The effect of nanoparticles on flashover characteristics and the relation between surface charging and surface flashover were also investigated. The results showed that the traps between nanoparticles and the polymer, which were introduced by the added nanoparticles, could cause surface charge accumulation. In addition, the flashover occurred at a lower voltage because of the accumulated charge on the sample surface. [ABSTRACT FROM AUTHOR]

Stationary DC electric fields are determined by the resistivity distribution of the insulation materials. In the presence of interfaces between different insulation materials, charge accumulation at these boundary layers may have a significant influence on the electric field distribution and with it on the breakdown strength of the arrangement. In many previous works, surface charging of model spacers was investigated. However, the ion flow problem to properly account for the electric conduction in the gas has not yet been solved. The role of different ion sources and the behavior of the resulting ion currents in the gas phase on the charge accumulation process have to be investigated in more detail. In this paper, the transient charge accumulation process on a PTFE spacer surface with a focus on charges originating from the gas phase is investigated experimentally and by simulations. These charges are produced by natural radiation. The transition of the ohmic conduction regime in the gas to a saturated ion current with increasing voltage is analyzed. Furthermore, the importance of additional charge sources like partial discharges and field emission from the electrodes is highlighted. The experimental results indicate that additional charges are generated already at voltage levels significantly below the measured PD inception voltage. These charges originate from micro discharges on the electrodes and have to be taken into account when designing HVDC GIS applications. [ABSTRACT FROM AUTHOR]

Polyimide film, as a special type of engineering plastic film, is a basic insulating material and is widely applied in the electrical and electronic industry. Addition of nanoparticles into polyimide can improve the insulating properties compared with undoped material. However, due to the change of the material structure, the trap characteristics and charge behavior are altered as a consequence. The existence of surface charge has a great effect on the breakdown characteristic and is the main reason leading to dielectric breakdown. Fluorination as change the chemical component in surface layer of polymers should give rise to the corresponding change in electrical properties of the surface layer thus influence the charge injection from electrodes when they are used as an insulator. This paper presents a study aimed at clarifying the effect of fluorination and nanoparticles on the surface charge accumulation and decay behaviors of fluorinated polyimide nanocomposite film. Samples were prepared by dispersing nano-scale Al2O3 into polyimides with weight percentages of 0, 1, 3, 5 and 7 respectively. Then the samples were surface fluorinated in a laboratory vessel at about 328 K (55 °) using a F2/N2> mixture with 20% F2 by volume and 0.05 MPa (500 mbar) for 30 minutes. Corona charging tests were performed at room temperature with a relative humidity of ˜ 40%. The charge distribution was measured by means of an electrostatic voltmeter. The results show the dependence of the charge density as well as the charge decay rate upon the fluorination and nanoparticle concentration, varying as a function of the charge polarity and charging time. It is suggested that the fluorination can significantly improve the decay rate of the surface charge in polyimide films. [ABSTRACT FROM AUTHOR]

Polymeric insulating materials exposed to pulse voltage with a nanosecond rise time in pulsed power have drawn increasing attention. Surface charge accumulation and decay on the charged polymers are very important parameters related to discharge. Nanocomposite technology has been used to improve the electrical properties of polymeric insulating materials. Therefore, it must be confirmed whether the nanosecond rise time of pulse voltage on the dynamic behaviour of surface charge on polymeric nanocomposites is different from that without nanoparticles. In this paper, we attempted to clarify the effect of the rise time on the electrical properties of epoxy/TiO2 nanocomposites focusing on surface charge accumulation and decay. Samples were prepared by dispersing nano-scale TiO2 particles into epoxy (EX) by mixing with shear force. Corona charging tests were performed at room temperature with a relative humidity of ~ 40%. The charge distribution was measured by means of an electrostatic voltmeter. The results show that the rise time plays an important role in the accumulating charge as well as the charge decay rate and varies with the concentration of nanoparticles and charge polarity. It is suggested that charge dynamics are dependent upon the rise time. [ABSTRACT FROM AUTHOR]

Effect of surface charges on dc flashover characteristics of a composite polymeric insulator is studied by means of experiments and theoretical calculations. The considered insulator consisted of a glass fiber reinforced epoxy core covered with a layer of silicone rubber and terminated by metallic electrodes with rounded smooth edges. In the experiments, the insulator surface was charged by external corona while keeping the electrodes grounded and different charging levels were realized by varying its intensity. A series of disruptive discharge tests were carried out on the charged insulator under negative dc voltages. It was revealed that negative deposited surface charges led to an enhancement of the flashover performance whereas positive ones reduced the flashover voltage level. A theoretical model has been developed and utilized for analyzing the experimental results. In the model, surface charge density profiles deduced from measured surface potential distributions were used as boundary conditions for calculations of electric fields. The measured and calculated flashover voltages were found to be in agreement indicating that the observed variations in the flashover characteristics could be attributed to the modifications of the electric field produced by the surface charges. [ABSTRACT FROM PUBLISHER]

Epoxy used as insulating material in electronic and electrical devices plays an important role in system reliability. Addition of nanoparticles into epoxy can improve the insulating properties compared with undoped material. However, due to the change of the material structure, trap characteristics and charge behaviors are altered as a consequence. This possibly leads to distortion of electric field that can result in degradation of the insulation. From the viewpoint of safety, it is necessary to investigate charge behavior of epoxy nanocomposites. This paper presents study aimed at clarifying the effect of nano-filler concentration on surface charge accumulation and decay behaviors of epoxy/TiO2 nanocomposites. Samples were prepared by dispersing nano-scale TiO22 into epoxy by mixing with shear force. Corona charging tests were performed at room temperature with a relative humidity of ˜ 40%. The charge distribution was measured by means of an electrostatic voltmeter. Obtained results show the dependence of the charge density as well as the charge decay rate upon the concentration of TiO22, varying as a function of the charge polarity, charging time and charging voltage. It is suggested that the charge dynamics is dependent upon the characteristics of localized surface states that are altered by the nanoparticles. [ABSTRACT FROM PUBLISHER]