Electrode For Detection Research Articles

Pencil‐Drawn Dual Electrode Detectors to Discriminate Between Analytes Comigrating on Paper‐Based Fluidic Devices but Undergoing Electrochemical Processes with Different Reversibility

AbstractA simple method is described to discriminate between analytes comigrating under on‐plate separation conditions, whose electrochemical behavior displays different reversible characters. It is based on the use of dual electrode detectors pencil‐drawn at the end of paper‐based fluidic channels defined by hydrophobic barriers. Simultaneous detection of comigrating species is achieved by applying to the upstream pencil‐drawn working electrode a potential for the oxidation (or reduction) of both analytes, while to the downstream pencil‐drawn working electrode a potential is imposed for the reverse process involving the product of the sole analyte undergoing a reversible enough electrochemical process. The performance of these inexpensive devices was preliminarily optimized by adopting hexacyanoferrate(II) as prototype species undergoing a reversible anodic process at carbon electrodes. They were then used as dual electrode detectors for thin‐layer chromatographic runs conducted on paper‐based microfluidic devices. Two types of synthetic solutions, one containing different contents of dopamine (DA) and ascorbic acid (AA) and the other of paracetamol (PA) and AA, were chosen as model samples. This choice was prompted us by the fact that in both cases these analytes comigrated under the adopted experimental conditions and required similar enough oxidation potentials. Nevertheless, DA and PA underwent reversible enough anodic processes while an irreversible electrochemical reaction is involved in the AA oxidation. Satisfactory results were found for both couples of target analytes, whose simultaneous detection was achieved within 230 s and was characterized by good enough repeatability and sensitivity. In particular, this approach appears to be well suited for the rapid and inexpensive assembling of electrochemical detectors for flow analysis systems.

Steady-state characteristics and transient response of MgZnO-based metal-semiconductor-metal solar-blind ultraviolet photodetector with three types of electrode structures

Detailed studies of MgZnO-based metal-semiconductor-metal (MSM) solar-blind ultraviolet photodetector with different electrode structures are performed. A two-dimensional physical model is established based on the Poisson's equation and time-dependent continuity equations, which is verified by our experimental data of conventional electrode MSM detector. The steady-state characteristics and transient response of semicircular and triangular electrode MSM detectors are also investigated by this model. Compared with the conventional electrode, semicircular and triangular electrode devices exhibit a substantial improvement on the photocurrent. At a bias of 10 V, the steady-state saturated photocurrents for semicircular and triangular electrode devices are 14.69 nA and 24.37 nA respectively, corresponding to a 20.5% and 100% increase over the conventional electrode detector. Meanwhile, the transient peak photocurrents reach 31.38 nA and 52.09 nA respectively, both of which are notably larger than that of conventional device.

Laser-processed three dimensional graphitic electrodes for diamond radiation detectors

We have used an original approach for diamond detectors where three dimensional buried graphitic electrodes are processed in the bulk of a diamond substrate via laser-induced graphitization. Prototype made of polycrystalline chemical vapor deposition diamond was fabricated using a nanosecond UV laser. Its charge collection efficiency was evaluated using α-particles emitted by a 241-Americium source. An improved charge collection efficiency was measured proving that laser micro-machining of diamond is a valid option for the future fabrication of three dimensional diamond detectors.

Functional study of glenohumeral ligaments

BackgroundThe glenohumeral ligaments are passive stabilising anatomical structures of the shoulder which, in synergy with the other active and passive stabilising structures, enable joint movement and cohesion. The purpose of this study is to analyse the isolated and synergic function of the glenohumeral ligaments by using a tetrapolar detection system with computer analysis. MethodsIn a study performed on cadavers after anatomical dissection, detector electrodes were positioned on the individual ligaments and recordings were made of bioelectric impedance and, consequently, the resistance, which is an indicator of the state of tension or relaxation of the ligamentous complex. Predefined positions of the upper limb were adopted—neutral adduction, adduction with external rotation, abduction at 45° with neutral and external rotation, and abduction at 90° with neutral and external rotation. ResultsThe superior glenohumeral ligament is important in stabilisation of the glenohumeral joint in adduction and external rotation. The middle glenohumeral ligament is an important stabilising structure in the positions of adduction and external rotation and abduction up to 45° in external rotation. The resistance, and therefore tension, of the inferior glenohumeral ligament, which is negligible in positions of neutral adduction and adduction in external rotation, increases in value for angles between 45° and 90°, indicating the important stabilising function of this ligament in those positions. ConclusionOur experimental study on cadavers, which involved evaluating the resistance of the glenohumeral ligaments by means of tetrapolar detection and computer analysis of the results, contributes to our knowledge of the functional activity of the anterior portion of the joint capsule.

Air-ion counter and mobility spectrometer

Mono-electrode self “zeroing” air-ion counter and mobility (size) scanning spectrometer (CDI-011) based on the Gerdien aspirated condenser principle has been developed. Instrument is intended for short- and long-term indoor and outdoor air-ion concentration measurements and scanning of air-ions by mobility. Measuring small currents (typically 10−14A) generated by the air-ions in outdoor conditions is demanding and causes many problems related to change of temperature, relative humidity, wind and electromagnetic noise. Also, measuring of both ion polarities with mono electrode detector require alternate changes of the polarizing voltage sign which produces capacitive current spikes. Various techniques, including “zeroing” method, have been applied to successfully overcome most of these measuring interferences.

Gate control and amplification of magnetoresistance in a three-terminal device

Gate control and amplification of magnetoresistance are demonstrated at room temperature in a fully epitaxial three-terminal GaAs-based device. In addition to the two ferromagnetic spin injector and detector electrodes of a MnAs/AlAs/GaAs:Mn/AlAs/MnAs vertical spin valve, a third non-magnetic gate electrode (Ti/Au) is placed directly on top of the heavily p-doped GaAs channel layer. The magnetoresistance of the device can be amplified to reach values as high as 500% at room temperature with the application of a bias to the gate terminal, which modulates the spin selectivity of the tunnel barriers. The experimental results are modeled by solving spin drift-diffusion and tunneling equations self consistently.

The relationship between ion current and temperature at the electrode gap

Abstract The relationship between ion current and local temperature was investigated with compressed natural gas (CNG) as a fuel. The ion current was measured using a pair of ignition electrodes and a pair of detector electrodes inside of a constant volume combustion bomb. The average temperature of the whole gas and the temperature at electrode gap were calculated using AVL-FIRE software. Meanwhile, flame development and pressure were recorded by a high-speed camera and a pressure sensor, respectively. The study indicates that, when ignition electrodes were used for detection, the current showed ignition, front-flame and post-flame stages. However, the ignition and part of the front-flame current were lost, when detector electrodes were used. The critical temperature for NO + generation and the appearance of post-flame current was about 2000 K. There were a linear relationship between the temperature and the number of NO + . With the increase in the distance between the two pair electrodes, the ion current and temperature decreased and the appearances of the front-flame and post-flame currents were postponed. The lower the temperature at the electrode gap was, the more obvious the influence of the contact area between the flame and the internal bomb wall on the post-flame current was.

Local and non-local magnetoresistance with spin precession in highly doped Si

We have demonstrated comparison of spin accumulation voltages in local and non-local (NL) magnetoresistance measurements without any spurious megnetoresistive signals. The spin transport length in a local measurement was larger than that in a NL measurement. An intensity of the local signals was explained by a conductivity mismatch theory. Depending on the relative magnetic configurations, Hanle-type spin precession signals in the local and the NL schemes showed a clear difference in signal shapes. The local transporting spins are accelerated in the direction of the electric field, and precess around the direction of the magnetic field under the detector electrode.

Cross-Talk Limits of Highly Segmented Semiconductor Detectors

Cross-talk limits of monolithic highly-segmented semiconductor detectors for high-resolution X-gamma spectrometry are investigated. Cross-talk causes false signal components yielding amplitude losses and fold-dependent shifts of the spectral lines, which partially spoil the spectroscopic performance of the detector. Two complementary electrical models are developed, which describe quantitatively the interchannel cross-talk of monolithic segmented detectors whose electrodes are read out by charge-sensitive preamplifiers. The first is here designated as Cross-Capacitance (CC) model, the second as Split-Charge (SC) model. The CC model builds around the parasitic capacitances C ij linking the preamplifier outputs and the neighbor channel inputs. The SC model builds around the finite-value of the decoupling capacitance C C used to read out the high-voltage detector electrode. The key parameters of the models are individuated and ideas are shown to minimize their impact. Using a quasi-coaxial germanium segmented detector it is found that the SC cross-talk becomes negligible for decoupling capacitances larger than 1 nF, where instead the CC cross-talk tends to dominate. The residual cross-talk may be reduced by minimization of stray capacitances C ij , through a careful design of the layout of the Printed Circuit Board (PCB) where the input transistors are mounted. C ij can be made as low as ~5 fF, but it is shown that even in such case the impact of the CC cross-talk on the detector performance is not negligible. Finally, an algorithm for cross-talk correction is presented and elaborated.

New BNL 3D-Trench electrode Si detectors for radiation hard detectors for sLHC and for X-ray applications

Abstract A new international-patent-pending (PCT/US2010/52887) detector type, named here as 3D-Trench electrode Si detectors, is proposed in this work. In this new 3D electrode configuration, one or both types of electrodes are etched as trenches deep into the Si (fully penetrating with SOI or supporting wafer, or non-fully penetrating into 50–90% of the thickness), instead of columns as in the conventional (“standard”) 3D electrode Si detectors. With trench etched electrodes, the electric field in the new 3D electrode detectors are well defined without low or zero field regions. Except near both surfaces of the detector, the electric field in the concentric type 3D-Trench electrode Si detectors is nearly radial with little or no angular dependence in the circular and hexangular (concentric-type) pixel cell geometries. In the case of parallel plate 3D trench pixels, the field is nearly linear (like the planar 2D electrode detectors), with simple and well-defined boundary conditions. Since each pixel cell in a 3D-Trench electrode detector is isolated from others by highly doped trenches, it is an electrically independent cell. Therefore, an alternative name “Independent Coaxial Detector Array”, or ICDA, is assigned to an array of 3D-Trench electrode detectors. The electric field in the detector can be reduced by a factor of nearly 10 with an optimal 3D-Trench configuration where the junction is on the surrounding trench side. The full depletion voltage in this optimal configuration can be up to 7 times less than that of a conventional 3D detector, and even a factor of two less than that of a 2D planar detector with a thickness the same as the electrode spacing in the 3D-Trench electrode detector. In the case of non-fully penetrating trench electrodes, the processing is true one-sided with backside being unprocessed. The charge loss due to the dead space associated with the trenches is insignificant as compared to that due to radiation-induced trapping in sLHC environment. Since the large electrode spacing (up to 500 μm) can be realized in the 3D-Trench electrode detector due to their advantage of greatly reduced full depletion voltage, detectors with large pixel cells (therefore small dead volume) can be made for applications in photon science (e.g. X-ray).

Highly Sensitive Potentiometric Strip Test for Detecting High Charge Density Impurities in Heparin

Contamination of heparin with oversulfated chondroitin sulfate (OSCS) became a matter of grave concern in the medical field after many fatal responses to OSCS tainted heparin products occurred during the 2007-2008 period. Even though standard lab-based analytical techniques such as nuclear magnetic resonance (NMR) and strong anion-exchange high performance liquid chromatography (SAX-HPLC) have proven useful for monitoring the OSCS content in heparin products, an easy-to-use, quick, portable, and cost-efficient method is still needed for on-site monitoring during and after the heparin production. In this report, a disposable strip-type electrochemical polyion sensor is described for detection of low levels of OSCS contamination in heparin. A magnetic actuator is incorporated into this simple electrode-based microfluidic device in order to create the mixing effect necessary to achieve equilibrium potential changes of the sensor within a microfluidic channel. The planar membrane electrode detector within the sample channel is prepared with a tridodecylmethylammonium chloride (TDMAC)-doped poly(vinyl chloride) (PVC) membrane essentially equivalent to previously reported polyanion-sensitive electrodes. When the concentration of heparin applied to the single-use strip device is 57 mg/mL (in only 20 μL of sample), the same concentration recommended in the NMR analysis protocol for detecting OSCS in heparin, the detection limit is 0.005 wt % of OSCS, which is ca. 20 times lower than the reported detection limit of the NMR method.

Nanoband electrode for high‐performance in‐channel amperometric detection in dual‐channel microchip capillary electrophoresis

A nanoband electrode detector integrated with a dual-channel polydimethylsiloxane microchip is proposed for in-channel amperometric detection in microchip capillary electrophoresis. Gold nanoband electrodes, which were fabricated on SU-8 substrates with a 100-nm-width gold layer, were introduced into the dual-channel microchip to be an electrochemical detector. Due to the nano-sized width of the detector, the noise of the amperometric detection was significantly reduced, and a high separation resolution was achieved for monitoring the analytes. The detection sensitivity of the system was improved by high signal-to-noise ratio, and a low detection limit on microchip was obtained for p-aminophenol (2.09 nM). Because of the high resolution in measuring half-peak width, the plate number that is used to evaluate the separation efficiency was 1.5-fold higher than that using 50-μm-width electrochemical detector. The effect of sample injection time and data acquisition time on separation efficiency was investigated, and an attractive separation efficiency was achieved with a plate number up to 17,500.

High-rate timing RPC with ceramics electrodes

A resistive plate counter for timing purposes in the high-rate environment of the Compressed Baryonic Matter Experiment has been developed at the Forschungszentrum Dresden-Rossendorf. The detector electrodes are made of a ceramics composite. Detector tests have been performed with minimum ionizing single electrons, delivered by the electron accelerator ELBE with a time accuracy of few picoseconds. The ceramics RPC shows an all-time high-rate capability for electron fluxes up to 2.7 × 10 5 s − 1 cm − 2 .

Very Black Infrared Detector from Vertically Aligned Carbon Nanotubes and Electric-Field Poling of Lithium Tantalate

Vertically aligned multiwall carbon nanotubes were grown by water-assisted chemical vapor deposition on a large-area lithium tantalate pyroelectric detector. The processing parameters are nominally identical to those by which others have achieved the "world's darkest substance" on a silicon substrate. The pyroelectric detector material, though a good candidate for such a coating, presents additional challenges and outcomes. After coating, a cycle of heating, electric field poling, and cooling was employed to restore the spontaneous polarization perpendicular to the detector electrodes. The detector responsivity is reported along with imaging as well as visible and infrared reflectance measurements of the detector and a silicon witness sample. We find that the detector responsivity is slightly compromised by the heat of processing and the coating properties are substrate dependent. However, it is possible to achieve nearly ideal values of detector reflectance uniformly less than 0.1% from 400 nm to 4 microm and less than 1% from 4 to 14 microm.

Ceramics high rate timing RPC

A resistive plate counter for timing purposes in the high rate environment of the Compressed Baryonic Matter Experiment has been developed at the Forschungszentrum Dresden-Rossendorf. The detector electrodes are made of a ceramics composite whose volume resistivity can be tuned in the production process over five orders of magnitude. The detector prototype has been tested with single electrons of 32 MeV. It shows an all-time high rate capability for electron fluxes up to 5×10 5 s −1 cm −2.

Development of CE–dual opposite carbon‐fiber micro‐disk electrode detection for peak purity assessment of polyphenols in red wine

A new dual opposite carbon-fiber micro-disk electrode detector was fabricated and tested for hyphenation with CE in the polyphenol determination. Under optimized conditions, CE-dual opposite carbon-fiber micro-disk electrode was found able to baseline separate and determine five important polyphenols (trans-resveratrol, (+)-catechin, (-)-epicatechin, quercetin and gallic acid) in red wine within 16 min with low detection limit (0.031-0.21 mg/L) and satisfactory repeatability (2.0-3.3% RSD, n=5). The opposite dual electrode enables simultaneous determination of CE eluents for current ratio measured at +0.8 and +1.0 V versus Ag/AgCl for the peak purity assessment. The capability to identify the presence of co-migrating impurities in given polyphenol peaks was demonstrated in a mixed standard solution with overlapping (+)-catechin and (-)-epicatechin peaks and in commercial red wine with unknown impurities and confirming the reliability for polyphenol quantitation in red wine with matching migration time and current ratio.

Microfluidic Polymer Chip with an Embedded Ion-Selective Electrode Detector for Nitrate-Ion Assay in Environmental Samples

A nitrate ion-selective electrode (NO(3)(-)-ISE) has been developed based on tetradodecylammonium bromide as an anion exchanger and 2-nitrophenyl octyl ether as a plasticizer. The NO(3)(-)-ISE shows an almost Nernstian response to nitrate ion over a concentration range between 1.0 x 10(-6) and 1.0 x 10(-1) M, with an anionic slope of -57.7 +/- 0.7 mV/decade. The selectivity coefficients of the NO(3)(-)-ISE for nitrate ion against chloride and sulfate (log k(NO(3)(-)Cl(-))(pot) = -2.42 and log k(NO(3)(-)SO(4)(2-))(pot) = -4.33) were obtained. A microfluidic polymer chip was fabricated using polystyrene plates and stainless-steel wires as a template for the channel. The microfluidic polymer chip is composed of a mixing chip and a NO(3)(-)-ISE detector chip. The microfluidic polymer chip, integrated with a NO(3)(-)-ISE detector consisting of the NO(3)(-)-ISE and a Na(+)-ISE as a reference electrode, showed an almost Nernstian response to nitrate ion over a concentration range between 1.0 x 10(-5) and 1.0 x 10(-1) M, with an anionic slope of -54.3 +/- 1.3 mV/decade. The microfluidic polymer chip was then applied to the determination of nitrate ion in environmental water samples, such as a tap water, a well-water sample and water for agricultural use.

Molecular Reaction Imaged by Scanning Atom Probe

Organic molecule system supported on metal substrate was analyzed by atom probe with two-dimensional ion detector and scanning extractor electrode (3D-SAP). The comparison of angular distribution of detected ions between molecular system and common metal tip showed a significant difference when AP analysis was performed by voltage pulsing. The influence of catalytic property of metal substrate also demonstrated by changing the substrate material. [DOI: 10.1380/ejssnt.2010.69]

Synthesis and Electrochemical Sensing Toward Heavy Metals of Bunch-like Bismuth Nanostructures

Large-scale bunch-like bismuth (Bi) nanostructures were the first time to be synthesized via two-step electrochemical deposition. The growth mechanism of the nanostructures was discussed. Such a designed bunch-like Bi electrode has high sensitivity to detect the heavy metal ions due to its unique three-dimensional structures and strong ability of adsorbing the heavy metal ions. The bunch-like Bi electrode’s detection of heavy metals was statically performed using anodic stripping voltammetry (ASV). The detection in the Pb(II) concentration range of 2.5–50 μg/l was also performed. Based on the experimental results, this bunch-like Bi electrode can be considered as an interesting alternative to common mercury electrodes and bismuth film electrodes for possible use in electrochemical studies and electroanalytical applications.

Determination of diethylene glycol in toothpaste by capillary electrophoresis with electrochemical detection

Diethylene glycol (DEG) can be determined in toothpaste via capillary electrophoresis at 16 kV using a fused silica capillary of 75 cm length and of 25 μm diameter along with a copper disc electrode detector operated at + 0.65 V (vs. SCE). DEG, propylene glyco1 and glycerol in a running buffer of pH 9.2 were separated within 17 min. The linear range for DEG is from 840 to to 4.2 μg·mL−1, and the detection limit (at S/N = 3) is 1.6 μg·mL−1 which therefore meets the safety limit. When applied to the analysis of DEG in toothpaste, the recoveries are between 96.9 and 103.0% for spiked samples and thus are quite satisfactory.