Dual Working Electrodes Research Articles

Disposable electrochemical aptasensor with mesoporous carbon spheres modified screen-printed dual-working electrodes for Pb2+ and Hg2+ detection

Electrochemical biosensing combined with screen-printed paper technology provides an effective strategy for the quantitative analysis of metal ions, particularly suitable for in-situ determination. In this study, a disposable, economical and user-friendly screen-printed dual-working electrodes (SPDEs) aptasensor system for the determination of lead ions (Pb2+) and mercury ions (Hg2+) was described. The sensor system consists of dual-working electrodes, a counter electrode and a reference electrode fabricated using screen printing technology. The aptasensor demonstrates high sensitivity and selectivity towards Pb2+ and Hg2+, owing to the larger specific surface area (1334.7 m2/g) and excellent conductivity of mesoporous carbon nanoparticles (MCNs). Additionally, the specific recognition ability and high affinity of G-quadruplex and T-Hg2+-T structures for Pb2+ and Hg2+, respectively, further enhance the performance. Under optimized experimental conditions, the aptasensor achieves a low limit of detection (LOD) of 0.088 ng/mL for Pb2+ and 0.0007 ng/mL for Hg2+ (S/N = 3), a wide linear range (0.1–1000.0 ng/mL for Pb2+ and 0.001–100.0 ng/mL for Hg2+), and high accuracy (relative standard deviation, RSD≤10.0 %) and selectivity. Importantly, the SPDEs aptasensor can detect Pb2+ and Hg2+ in a sample without competition and interference, achieving accuracy comparable to that of commercial inductively coupled plasma mass spectrometry (ICP-MS). These advantages make the SPDEs aptasensor highly suitable for practical applications in environmental monitoring, food safety, and clinical diagnosis.

Electrochemical sensing performance of two CuO nanomaterial-modified dual-working electrodes.

Two CuO nanostructures, namely, nanospheres (CuONSs) and nanochains (CuONCs) with different shapes but similar diameters, were synthesized and characterized. With these two nanomaterials as electrode modifiers, a systematic comparative study was conducted to examine their electrochemical sensing of catechol (CT) using a dual-working electrode system. The results suggest that for CuONS- and CuONC-modified glassy carbon electrodes, the electrode process for the CT redox is diffusion-controlled, and the modification amount and electrolyte pH have a similar effect on the response. However, the CuONCs showed a higher peak current and lower peak potential, as well as a lower detection limit for the electrochemical oxidation of CT. This is explained by the lower charge transfer impedance and higher electroactive surface area of the CuONCs. Notably, an unexpected peak appeared in the cyclic voltammograms when the pH was <4 for the CuONCs and <3 for the CuONSs. For this phenomenon, UV-Vis spectra, zeta potential, and size distribution experiments demonstrated changes in the two CuO nanostructures at lower pH, illustrating that CuONSs can tolerate a higher pH as compared to CuONCs. The multiple comparisons between the two nanomaterials presented here can provide references for the selection of electrochemical sensing materials.

A stretchable wearable sensor with dual working electrodes for reliable detection of uric acid in sweat

Wearable sweat sensors with stretch capabilities and robust performances are desired for continuous monitoring of human health, and it remains a challenge for sweat sensors to detect targets reliably in both static and dynamic states. Herein, a flexible sweat sensor was created using a cost-effective approach involving the utilization of three-dimensional graphene foam and polydimethylsiloxane (PDMS). The flexible electrochemical sensor was fabricated based on PDMS and Pt/Pd nanoparticles modified 3D graphene foam for the detection of uric acid in sweat. Pt/Pd nanoparticles were electrodeposited on the graphene foam to markedly enhance the electrocatalytic activity for uric acid detection. The graphene foam with excellent electrical property and high porosity, and PDMS with an ideal mechanical property endow the sensing device with high stretchability (tolerable strain up to 110 %), high sensitivity (0.87 μA μM−1 cm−2), and stability (remaining unchanged for more than 5000 cycles) for daily wear. To eliminate possible interferences, the wearable sensor was designed with dual working electrodes, and their response difference ensured reliable and accurate detection of targets. This strategy of constructing sweat sensors with dual working electrodes based on the flexible composite material represents a promising way for the development of robust wearable sensing devices.

Electrochemical lateral flow immunosensor with enhanced reproducibility for milk allergen detection

Electrochemical lateral flow platforms are applied for many applications due to their advantages of higher sensitivity in electrochemical detection than in conventional test strips. However, these devices have low reproducibility since the interface between the test strips and the electrode is difficult to replicate. Herein, for the first time, dual-working electrodes on a lateral flow immunoassay (dWE-LFIA) were used as an internal current on a single device, in which the current of both working electrodes was calculated as a normalized current to increase the device-to-device reproducibility. In this work, the detection of β-lactoglobulin, an allergen found in milk, was used as a model for evaluating the efficacy of dWE-LFIA. A study of reproducibility using this device showed a surprising 15-fold %RSD improvement compared to a single electrode on LFIA. Moreover, the analytical performance of this sensor for detecting β-lactoglobulin exhibited a wide linearity range of 1–1000 ng/mL and a detection resolution of 0.31 ng/mL. Therefore, our design of dWE-LFIA exhibited outstanding performance of high reproducibility, had high sensitivity detection, and could be applied and further developed for commercial biosensors in the future.

Integrated solar-powered MEMS-based photoelectrochemical immunoassay for point-of-care testing of cTnI protein

Considering the fact that acute myocardial infarction has shown a trend towards younger age and has become a major health problem, it is necessary to develop rapid screening devices to meet the needs of community health care. Herein, we developed an artificial neural network-assisted solar-powered photoelectrochemical (SP-PEC) sensing platform for rapid screening of cardiac troponin I (cTnI) protein in the prognosis of patients with acute myocardial infarction (AMI) by integrating a self-powered photoelectric signal output system with low-cost screen-printed paper electrodes functionalized with ultrathin Bi2O2S (BOS) nanosheets. An integrated solar-powered PEC immunoassay with micro-electro-mechanical system (MEMS) was constructed without an excitation light source. The quantification of cTnI protein was obtained by the electrical signal changes caused by the electro-oxidation process of H2O2, generated by the classical split immune reaction, on the electrode surface. The test electrodes were developed as dual working electrodes, one for target cTnI testing and the other for evaluating light intensity, to reduce the temporal inconsistency of sunlight. The photoelectrodes were discovered to exhibit satisfactory negative response to target concentrations in the dynamic range of 2.0 pg mL−1-10 ng mL−1 since being regressed in an improved artificial neural network (ANN) model using the pooled dataset of target signals affected by the light source. The difference of hot electron and hole transfer behavior in different thickness of nano-materials was determined by finite element analysis (FEA), which provided a theoretical basis for the development of efficient PEC sensors. This work presents a unique perspective for the design of a revolutionary low-cost bioassay platform by inventively illuminating the PEC biosensor's component process without the use of light.

Gel polymer electrolyte for reversible metal electrodeposition dynamic windows enables dual-working electrodes for faster switching and reflectivity control

Dynamic windows based on reversible metal electrodeposition are an attractive way to enhance the energy efficiency of buildings and show great commercial potential. Dynamic windows that rely on liquid electrolytes are at risk of short circuiting when two electrodes contact, especially at larger-scale. Here we developed a poly (vinyl alcohol) (PVA) gel polymer electrolyte (GPE) with 85% transmittance, that is, sufficiently stiff to act as a separator. The GPE is implemented into windows that exhibit comparable electrochemical and optical properties to windows using a liquid electrolyte. Furthermore, the GPE enables the fabrication of windows with dual-working electrodes (WE) and a metal mesh counter electrode in the center without short-circuiting. Our dual-WE PVA GPE window reaches the 0.1% transmittance state in 101 s, more than twice the speed of liquid windows with one working electrode (207 s). Additionally, each side of the dual-WE GPE window can be tinted individually to demonstrate varied optical effects (i.e., more reflective, or more absorptive), providing users and intelligent building systems with greater control over the appearance and performance of the windows in a single device architecture.

Multiplexed Anodic Stripping Voltammetry Detection of Heavy Metals in Water Using Nanocomposites Modified Screen-Printed Electrodes Integrated With a 3D-Printed Flow Cell.

In this study, we present multiplexed anodic stripping voltammetry (ASV) detection of heavy metal ions (HMIs)—As(III), Cd(II), and Pb(II)—using a homemade electrochemical cell consisting of dual working, reference and counter screen-printed electrodes (SPE) on polyimide substrate integrated with a 3D-printed flow cell. Working and counter electrodes were fabricated by the screen-printing of graphite paste while the Ag/AgCl paste was screen-printed as a reference electrode (Ag/AgCl quasi-reference electrode). The working electrodes were modified with (BiO)2CO3-reduced graphene oxide (rGO)-Nafion [(BiO)2CO3-rGO-Nafion] and Fe3O4 magnetic nanoparticles (Fe3O4MNPs) decorated Au nanoparticles (AuNPs)-ionic liquid (IL) (Fe3O4-Au-IL) nanocomposites separately to enhance HMIs sensing. Electrochemical detection was achieved using square wave ASV technique. The desired structure of the flow electrochemical cell was optimized by the computational fluid dynamic (CFD). Different experimental parameters for stripping analysis of HMIs were optimized including deposition time, deposition potential and flow rate. The linear range of calibration curves with the sensing nanocomposites modified SPE for the three metal ions was from 0–50 μg/L. The limits of detection (S/N = 3) were estimated to be 2.4 μg/L for As(III), 1.2 μg/L for Pb(II) and 0.8 μg/L for Cd(II). Furthermore, the homemade flow anodic stripping sensor platform was used to detect HMIs in simulated river water with a 95–101% recovery, indicating high selectivity and accuracy and great potential for applicability even in complex matrices.

Printed circuit board integrated wearable ion-selective electrode with potential treatment for highly repeatable sweat monitoring

Wearable chemical sensors have recently received great attention, especially on monitoring ion concentration in sweat. However, challenges still remain, such as the nonnegligible potential deviation of the ion-selective electrode (ISE) based potentiometric sensor after multi-use. Herein, we propose an easily prepared and highly integrated wearable solid contact-ISE (SC-ISE), allowing multiple measurements with repeatable open circuit potential (OCP), which is achieved by applying a positive potential on the working electrode. It’s believed that the positive potential alters the oxidation-reduction state of the conducting polymer. The integrated SC-ISE sensor is fabricated on a printed circuit board (PCB) substrate, eliminating external hardware. Preparation of the sensor electrode adopts a standard route, i.e. employing the electroless nickel immersion gold (ENIG) process for plating gold layers. Dual working electrodes have been designed to measure either sodium or potassium ion. This wearable platform has been validated through on-body tests by monitoring ion levels in the real sweat.

Probing the distribution of redox in the diffusion layer of the substrate electrode by the scanning electrochemical microscopy

Taking advantage of the dual working electrodes and the precise positioning of the tip electrode of the scanning electrochemical microscopy, the distribution of ferrocenemethanol in the diffusion layer of the substrate electrode is studied when the substrate potential is applied. When the co-directional potential is applied to the substrate, the closer to the surface of the substrate electrode, the less the amount of ferrocenemethanol. Because the reaction of the substrate electrode and the tip electrode is the same, they compete with each other. When the reverse potential is applied to the substrate electrode, the closer to the surface of the substrate electrode, the more the amount of ferrocenemethanol. Because the reaction of the substrate electrode can regenrate ferrocenemethanol.

Novel electrochemical sensor using a dual-working electrode system for the simultaneous determination of glucose, uric acid and dopamine

Dual working electrodes were constructed for the simultaneous determination of three analytes. A graphene oxide-modified glassy carbon electrode (GO/GCE) was used for adsorptive anodic stripping voltammetry to detect uric acid and dopamine, while a chitosan/glucose oxidase/Prussian blue-graphite modified glassy carbon electrode (Chi/GOx/PB-G/GCE) was used for chronoamperometric glucose detection. The fabrication and operation conditions for both electrodes were optimized. Linearity was obtained in the ranges of 0.10–30 µM and 30–80 µM for dopamine, 0.20–10 µM and 10–30 µM for uric acid and 15–1,500 µM for glucose. The system provided detection limits (LOD = 3σ/S) of 0.080 µM, 0.11 µM, and 5.7 µM for dopamine, uric acid and glucose, respectively. This dual-working electrode system showed good reproducibility and excellent recovery for the simultaneous determination of dopamine, uric acid, and glucose. When used to analyze dopamine, uric acid, and glucose in blood plasma samples, the results agreed well with those from conventional methods (P > 0.05), indicating the potential of this system to simultaneously determine these three analytes in real samples.

Design of dual working electrodes for concentration process in metalloimmunoassay

Electrochemical immunosensing, particularly through a metalloimmunoassay, is a promising approach for development of point-of-care (POC) diagnostics devices. This study investigated the structure of dual working electrodes (W1 and W2), used in a silver nanoparticles-labeled sandwich-type immunoassay and silver concentration process, paying special attention to the position of W1 relative to W2. The new structures of the dual working electrodes were fabricated for efficient silver concentration and evaluated experimentally, which showed that the duration of prereduction before current measurement decreased from 480s to 300s by transforming the position of W1 from 1 line to 2 lines or 6 parts. The experimental results were also compared with numerical simulations based on three-dimensional diffusion, and the prereduction step almost followed the three-dimensional diffusion equation. Using numerical simulations, the ideal structures of dual working electrodes were designed based on relationships between the structures and duration of prereduction or the LOD. In the case of 36 lines at an area ratio of W1 to W1+W2 of 1 to 10, the prereduction duration decreased to 96s. The dual working electrodes designed in this study promise to shorten the total analysis time and lower the LOD for POC diagnostics.

Spatially-Resolved Interfacial Electrochemistry: Ohmic Microscopy

A method is herein described that allows spatially resolved capacitive currents at electrode|electrolyte interfaces to be recorded in situ by monitoring the ohmic drop in the electrolyte, Δφsol, using two microreference electrodes. Measurements were performed in 0.1 M H2SO4 aqueous solutions using Au and Pt either as single or dual working electrodes, that is, connected to one another, in an otherwise conventional three-electrode electrochemical cell. Plots of Δφsol versus E, the potential of the dual Au|Pt electrode with respect to the main reference electrode, recorded during voltammetric cycles, yielded curves bearing features characteristic of the Au|0.1 M H2SO4 or Pt|0.1 M H2SO4 interface depending on whether the microreference electrodes were placed close to the Au or Pt electrode surface, respectively. Extensions of this methodology to measurements in the micrometer domain are discussed briefly.

Disposable screen-printed enzyme sensor for simultaneous determination of starch and glucose

A disposable screen-printed biosensor with dual working electrodes was first established for simultaneous determination of starch and glucose. The electrochemical behavior of the sensor was assessed using cyclic voltammetry and chronoamperometry. The linear response ranges of the sensor were up to 0.4% (w/v) starch and 20 mmol glucose 1−1. Real samples were analysed using the proposed method and the reference method and the correlation coefficient was 0.997.

On-Column Reduction of Catecholamine Quinones in Stainless Steel Columns during Liquid Chromatography

The chromatographic behavior of quinones derived from the oxidation of dopamine and N-acetyldopamine has been studied using liquid chromatography (LC) with both a diode array detector and an electrochemical detector that has parallel dual working electrodes. When stainless steel columns are used, an anodic peak for the oxidation of the catecholamine is observed at the same retention time as a cathodic peak for the reduction of the catecholamine quinone. In addition, the anodic peak exhibits a tail that extends to a second anodic peak for the catecholamine. The latter peak occurs at the normal retention time of the catecholamine. The origin of this phenomenon has been studied and metallic iron in the stainless steel components of the LC system has been found to reduce the quinones to their corresponding catecholamines. The simultaneous appearance of a cathodic peak for the reduction of catecholamine quinone and an anodic peak for the oxidation of the corresponding catecholamine occurs when metallic iron in the exit frit reduces some of the quinones as the latter exits the column. This phenomenon is designated as the "concurrent anodic-cathodic response." It is also observed for quinones of 3,4-dihydroxyphenylalanine, 2,4,5-trihydroxyphenylalanine, 3,4-dihydroxyphenylpropenoic acid, and 3,4-dihydroxybenzoic acid and probably occurs with o- or p-quinones of other dihydroxyphenyl compounds. The use of nonferrous components in LC systems is recommended to eliminate possible on-column reduction of quinones.

The use of differential measurements with a glucose biosensor for interference compensation during glucose determinations by flow injection analysis

A novel detection system for the determination of glucose in the presence of clinically important interferents, based on the use of dual sensors and flow-injection analysis (FIA), is described. The normalisation methodology involves measurement of the interference signal at a reference sensor; this signal can then be subtracted from the glucose sensor signal (post-run) to give a corrected measurement of the glucose concentration. The detection system consists of a thin layer cell with dual glassy carbon working electrodes. One electrode was surface modified to act asglucose biosensor by immobilisation of glucose oxidase (GOx) (from Aspergillus niger) with 1% glutaraldehyde and bovine serum albumin. The second electrode (glucose oxidase omitted) was utilised to measure the interference signal responding only to electroactive species present in the injected sample. A computer controlled multichannel potentiostat was used for potential application and current monitoring duties. The sensor responses were saved in ASCII format to facilitate post-run analysis in Microsoft Excel. Cyclic voltammetry (CV) was utilised to investigate the manner in which the interference signal contributed to the total signal obtained at the biosensor in the presence of glucose. The kinetic parameters Imax and the apparent Michaelis-Menten constant, K′m, were calculated for the sensor operating under flow-injection conditions.

Determination of traces of iron by thin-layer spectroelectrochemistry

The complex of iron with Chrome Azurol S (CAS) was studied using a long path-length thin-layer spectroelectrochemical cell with dual working electrodes. A method for the determination of traces of iron proposed, based on the variation in the absorbance between the oxidized and reduced state of the complex (Δ A), Δ A was proportional to iron concentration over the range 0–3 μg ml −1. Compared with the conventional spectrophotometric determination of iron using CAS, the selectivity was improved because the analytical signal here depended on both the spectral and the electrochemical behaviour of the tested species. Iron was determined in water samples by this method. A concept characterizing the sensitivity of the spectroelectrochemical signals is also presented.

Characterization of multiple carbon fibre microelectrodes in a flow-through cell and amperometric detection with dilute electrolyte for liquid chromatography

A simple, convenient and sensitive flow-through cell incorporating multiple carbon fibres in a polyvinyl chloride tube was constructed for high performance liquid chromatography. The voltammetric behaviour, electrode treatment, stability and hydrodynamic voltammograms of such electrodes are discussed. An in-situ electrochemical pretreatment is proposed for activation and recovery of the activity of the carbon fibre electrode in flow-stream detection. The desirable detector was found to be nearly flow-rate independent. Catecholamines can be detected at concentrations as low as 2 × 10 −9 M. The cell could be used in the mobile phase with little electrolyte. It was found that the solution resistance in the flow pathway was the major source of distortion of the shape of hydrodynamic voltammograms and of high noise at dilute electrolyte. Parallel detection using dual working electrodes is demonstrated for reversed-phase chromatographic separation of catecholamines.

Determination of urinary vanillylmandelic acid by direct injection and coupled-column chromatography with electrochemical detection

An automated column-switching system for determination of vanillylmandelic acid in urine is described. The liquid chromatographic system was composed of two separation columns with different selectivity properties, an octadecyl column coated with tributyl phosphate as stationary liquid phase and a silica-based anion exchanger. Urine samples were injected directly onto the first column, where vanillylmandelic acid was separated from the main part of the sample matrix. The internal standard isovanillylmandelic acid was co-eluting with vanillylmandelic acid, and a fraction of the eluate containing both substances was switched to the second column, where separation was performed. To assess peak purity, detection was performed with dual working electrodes in parallel mode. A relative standard deviation of 3.5% was obtained for determination of human urine samples containing 3 microM vanillylmandelic acid, and less than 0.1 microM could be detected.

Cyclic voltammetry for reversible redox-electrode reactions in thin-layer cells with closely separated working and auxiliary electrodes of the same size

The characteristics of a thin-layer cell with a planar auxiliary electrode placed opposite a planar working electrode are quite similar to those of a thin-layer cell with dual working electrodes, i.e. regeneration of the redox species takes place and a steady-state current is established. Theoretical equations are derived for cyclic voltammetry for a reversible redox system at this thin-layer configuration. The shape of the voltammograms depends on a single dimensionless parameter, p = nFvδ 2/ RTD, where δ is the distance between the working and the auxiliary electrodes, v is the potential sweep rate and D is the diffusion coefficient. When p is less than 2, no peak appears on the forward sweep of the voltammogram. At the other limit, when p is greater than 15 the peak current and peak potential values are the same as those for semi-infinite diffusion. Good agreement between the theoretical and experimental results has been obtained for the hexacyanoferrate(II/III) system. Using voltammetry, both the inter-electrode distance δ and the diffusion coefficient of the substrate may be found simultaneously.

Simultaneous multiple electrode liquid chromatographic—electrochemical assay for catecholamines, indoleamines and metabolites in brain tissue

To enhance the selectivity of liquid chromatographic—electrochemical assays for biogenic amines and metabolites in brain tissue, multiple electrode transducers were investigated. Two configurations of dual working electrodes were examined: parallel—adjacent and series arrangements. Using the raw detector currents with each configuration, peak-height ratios from simultaneously generated chromatograms were calculated to assess the selectivity of the instrument for direct injections of brain tissue supernatant. Ratios were consistent with injections of standards. Nearly coeluting peaks such as norepinephrine and 3-methoxy-4-hydroxyphenylglycol were resolved by using dual detector electrodes in series; only the catecholamines were detected at the downstream electrode owing to their electrochemical reversibility. The scheme was applicable to the assay of norepinephrine, 3,4-dihydroxyphenylacetic acid, dopamine, homovanillic acid, serotonin, 5-hydroxytryptophan and 5-hydroxyindole-3-acetic acid in brain tissue in less than 15 min.