Interdigitated Electrode Array Based Sensors for Monitoring of Caesium

High-sensitivity electrochemical enzyme-linked assay on a microfluidic interdigitated microelectrode

An interdigitated microelectrode array (IDA) biamperometric titration is presented for the microdetermination of formaldehyde. It is based on a direct titration of formaldehyde with hydroxylamine under the formation of formaldoxime. The released hydrogen cations react with hydroxyl anions in 0.1 M NaOH. The interdigitated pair of two individually polarizable microelectrodes serves as a biamperometric end-point indicator. Hydroxylamine together with dissolved free oxygen behave as a quasi reversible mixed redox system, therefore a significant increase of current flowing between the IDA segments polarized by 100 mV is observed when the first excess of titrant appears in the titrated solution. Because of the small dimension of the IDA sensor this principle can be extended for a microanalytical variant of this method. Formaldehyde contents down to 10−3 M in small volume waste water samples could be determined by this technique. These samples usually contain carboxylic acids which interfere in iodimetric determinations, but do not influence the titration of formaldehyde with hydroxylamine.

Experimental studies of sorption on water treatment from ammonium ions by a calcined sorbent based on ash-and-slag waste from thermal power engineering have been carried out. The calcined sorbent was obtained by calcining samples of ash-and-slag from coal combustion at the Novocherkassk State District Power Plant at a temperature of 600 оC for 30 min. The sorption capacity of a sorbent with a dose of 2.0 g per 50 mL of a model solution, a stirrer speed of 200 rpm, pH 7, and sorption time from 10 to 180 minutes was studied. The influence of the initial concentration of model solutions with the content of ammonium ions 5, 20, 50 and 100 mg/L on the amount of adsorption and treatment efficiency was studied. The highest treatment efficiency of 60% was obtained for an initial concentration of ammonium ions in a solution of 20 mg/L. Processing of experimental data was carried out according to the models of pseudo-first, pseudo-second-order and intra-particle diffusion kinetics. The best description of the experimental data was obtained using the pseudo-first order model, which has the highest value of the coefficient of determination. The adsorption equilibrium in the system ammonium ions – calcined sorbent was studied for the initial concentration of ammonium ions in solution: 5, 20, 30, 50, 100, 200, 300 mg/L. Processing of experimental data on equilibrium was carried out on the basis of two-parameter adsorption isotherms: Langmuir, Freindlich and Temkin. The value of the coefficient of determination according to the Langmuir isotherm is the largest R2 = 0.9904. Dependences between the cleaning efficiency at adsorption equilibrium and the initial concentration of ammonium ions in solution for the system ammonium ions – calcined sorbent are obtained. With an increase in the initial concentration of ammonium ions in the solution, the treatment efficiency at low initial concentrations increases, and decreases with increasing concentration.

Rapid analysis of perchlorate, chlorate and bromate ions in concentrated sodium hypochlorite solutions

A microfluidic flow cell with embedded gold interdigitated array microelectrode (IDAM) was developed and integrated with magnetic nanoparticle-antibody conjugates (MNAC) into an impedance biosensor to rapidly detect pathogenic bacteria in ground beef samples. The flow cell consisting of a detection microchamber and inlet and outlet microchannels was fabricated by bonding an IDAM chip to a poly(dimethylsiloxane) (PDMS) microchannel. The detection microchamber with a dimension of 6 mm × 0.5 mm × 0.02 mm and a volume of 60 nL was used to collect bacterial cells in the active layer above the microelectrode for sensitive impedance change. MNAC were prepared by conjugating streptavidin-coated magnetic nanoparticles with biotin-labeled polyclonal goat anti-E. coli antibodies and were used in the separation and concentration of target bacteria. The cells of E. coli O157:H7 inoculated in a food sample were first captured by the MNAC, separated, and concentrated by applying a magnetic field, washed, and then suspended in mannitol solution and finally injected through the microfluidic flow cell for impedance measurement. This impedance biosensor was able to detect as low as 1.6 × 102 and 1.2 × 103 cells of E. coli O157:H7 cells present in pure culture and ground beef sample, respectively. The total detection time from sampling to measurement was 35 min. Equivalent circuit analysis indicated that the bulk medium resistance, double layer capacitance, and dielectric capacitance were responsible for the impedance change due to the presence of E. coli O157:H7 cells on the surface of IDAM. Sample pre-enrichment, secondary antibodies on the microelectrode surface, and redox probes were not required in this impedance biosensor.

Dynamics of diffusive soil phosphorus in two grassland experiments determined both in field and laboratory conditions

IntroductionBipolar electrochemistry is an attractive technique to realize simultaneous multiplexed detection. In bipolar electrochemical systems, a potential gradient is formed in a solution. When an isolated electrode (bipolar electrode: BPE) that is not in contact with an external device is placed in the potential gradient, potential difference is generated at the interface between the BPE and the solution (Figure 1(A)), which can be a motive force to make anodic and cathodic reactions to proceed on the BPE (Figure 1(B)) [1]. The progress of reduction reactions on the cathodic pole can be measured by coupling the reaction with electrochemiluminescence (ECL) [2]. Although the simple single electrode configuration is attractive in realizing a large array of BPEs, an issue is that the interfacial potential difference on the BPE is not controlled intentionally. In other words, the potential profile in the solution can vary as expressed by 1, 2, and 3, although the potential difference between the two poles is the same for all cases (Figure 1(C)). To solve this problem, we used an ion-selective membrane (ISM) on a part of the BPE. The ISM has an effect to fix the interfacial potential difference there without current generation through the interface (Figure 1(D)). Method Arrays of BPEs were formed with platinum (Pt) or gold (Au). An ISM was formed on a part of each BPE. The surface of the BPE was insulated with polyimide layer except for the anodic and cathodic poles and the active area of the ISM. We previously tested the use of thin-film Ag/AgCl instead of the ISM. However, a problem was that current flowed through the interface due to its non-polarized nature, affecting the ECL intensity. With regard to this, current does not flow through the ISM/solution interface. The location of the ISM was changed with BPEs of the same length (Figure 2(A)). Otherwise, BPEs of different lengths were fabricated, and the location of the ISM was kept constant between the ISM and the cathodic pole (Figure 2(B)).The active areas on the BPEs were cleaned and the cleanliness was checked by taking cyclic voltammograms (CV) in a solution containing 100 mM KCl and 10 mM K3[Fe(CN)6]. To form the ISM, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS) was first coated on an exposed area of the BPE. To form the ISM, 20 µl of Na+ ionophore cocktail containing 89.5% 2-Nitrophenyl octyl ether, 10.0% sodium ionophore II, and 0.5% sodium tetraphenylborate (w/w) (Sigma-Aldrich (Japan)) was dissolved in 79.3% polyvinyl chloride (PVC) and tetrahydrofuran (PVC/THF) solution. The solution was dropped onto the PEDOT/PSS layer to form the ISM and was dried.Figure 3 shows the setup used for the experiment. Pt wires (diameter: 0.5 mm) were used for the driving electrodes. The distance between the driving electrodes was 30 mm. For ECL, 10 mM PBS (pH 6.9) containing 5.0 mM tripropylamine (TPA) and 1.0 mM [Ru(bpy)3]2+ was used. As an analyte, oxygen dissolved in the solution was used. To change the interfacial potential difference at the ISM, Na+ ions of different concentrations were added to the solution. Before injecting the solution in the reaction chamber, the solution was stirred for at least 30 min to saturate air. Pictures of ECL were taken immediately after the application of the voltage with 60 s exposure. The experiments were conducted at 25°C. Results and Conclusions The potential of the ISM was checked using a BPE with an ISM by measuring the potential in NaCl solutions of various concentrations with respect to a commercial liquid junction Ag/AgCl electrode. Figure 4 shows the dependence of the potential of the ISE on the concentration of Na+ ions. The slope was 59.0 mV/decade, which was very close to the value expected from the Nernst equation. The effect of placing the ISM on a part of the BPE was investigated using BPEs of the same length. ECL intensity changed depending on the location of the ISM (Figure 5). Figure 6 shows ECL observed using BPEs of different length maintaining the distance between ISM and the cathodic pole. In both cases, the effect of placing the ISM was clearly observed and the ECL intensity was strongest when the distance between the ISM and the anodic pole is longer. These results indicate that the ECL intensity can actually be controlled by the ISM. We have tested other electrode configurations. The results will also be presented.The potential control developed in this study is also effective to control the electrode potentials in closed BPE systems in which solutions are separated in different compartments.

Bipolar electrochemistry is promising in realizing simultaneous multiplexed detection. In open bipolar systems, a potential gradient is formed in a solution. When an isolated electrode (bipolar electrode: BPE) that is not in contact with an external device is placed in the potential gradient, interfacial potential difference develops between the BPE and the solution (Figure 1A). As a result, oxidation and reduction reactions occur simultaneously on both poles (Figure 1B) [1]. The progress of the reduction reaction on the cathodic pole can be measured by coupling the reaction with a reaction that generates electrochemiluminescence (ECL) [2]. However, a problem with this method is that the interfacial potential difference on the BPE is not precisely controlled. In other words, the potential profile with respect to the electrode potential changes (Figure 1C). To solve this problem, we used an ion-selective membrane (ISM) on a part of the BPE. The ISM has an effect to fix the interfacial potential difference at the location without current generation through the interface (Figure 1D).Arrays of BPEs were formed with gold and Na+ ISM was formed on a part of each BPE. The surface of the BPE was insulated with a polyimide layer except for the anodic and cathodic poles and the active area of the ISM. To form the ISM, a layer of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS) was first coated on an exposed area of the BPE. The Na+ ISM was formed on the PEDOT/PSS layer. The solution to form the ISM contained 43.97 wt% polyvinyl chloride (PVC) dissolved in 1 mL tetrahydrofuran (THF). 53.38 wt% of nitrophenyl octyl ether (NPOE), 2.04 wt% of sodium ionophore X, and 0.61 wt% (w/w) of sodium tetrakis(4-fluorophenyl)borate (NaTFPB) were added to the PVC solution and mixed well. After forming the ISM, its peripheries were fixed with a silicone adhesive.In the experimental setup shown in Figure 1A, platinum wires (diameter: 0.5 mm) were used for the driving electrodes. The distance between the driving electrodes was 30 mm. To cause the ECL reaction, 10 mM phosphate buffer solution (pH 6.9) containing 5.0 mM tripropylamine (TPA) and 1.0 mM [Ru(bpy)3]2+ was used. Oxygen dissolved in the solution was used as an analyte. The experiments were conducted at 25°C.To control the potential of the BPEs, we previously used Ag/AgCl for the potential control. However, a problem was that current flowed through the non-polarizable metal/solution interface, affecting the ECL intensity. With regard to this, the ISM is superior because current does not flow. The effect of placing the ISM on a part of the BPE was first examined using BPEs of the same length and changing the location of the ISM (Figure 2). The ion selective electrode (ISE) was effective and the ECL intensity changed by changing the location of the ISE. The effect of the ISM was also demonstrated using folded double BPE structures with the ISM formed at either or both ends. Brighter ECL was observed with the folded structure compared with a single BPE. From these experiments, the effect of placing the ISM on BPEs was clearly observed. As an application to biosensing, we also tested the detection of glucose by immobilizing glucose oxidase and osmium polymer on the cathodic pole. The ECL was also observed accompanying the production of hydrogen peroxide by glucose oxidase and following the reduction of hydrogen peroxide.The effect of placing the ISM was also examined in closed bipolar systems. In the closed bipolar systems, solutions in the cathode and anode side are separated in different compartments. In this study, 15 mm-long electrodes were used and the electrodes extended in the two compartments. The anodic pole was exposed to the solution for ECL, whereas the cathodic pole was immersed in a Na2SO4 solution. A voltage (2.4 V) was applied between the driving electrodes immersed at the end of the solutions. The brightest ECL was observed on the BPE with the ISM nearest to the cathodic pole. The result indicates that the ISM is also effective in controlling the potential for closed bipolar systems.[1] S. E. Fosdick, K. N. Knust, K. Scida, R. M. Crooks. Bipolar electrochemistry. Angewandte Chemie International Edition, 52 (2013) 10438-10456. doi:10.1002/anie.201300947[2] K. F. Chow, F. Mavré, R. M. Crooks. Wireless electrochemical DNA microarray sensor. Journal of the American Chemical Society, 130 (2008) 7544-7545. doi:10.121/ja802013q Figure 1

Fluoride ions are used in battery electrolytes in fluoride shuttle batteries. Since organic solvents are used in battery electrolytes, there is a growing demand to develop appropriate methods for quantifying fluoride ion concentration in organic solvents. In this study, a fluoride ion-selective electrode (ISE) for organic solutions is proposed as an electrode of the second kind. A Ag|AgF electrode was made via the anodization of a silver wire in propylene carbonate (PC) containing dissolved fluoride ions. The resultant electrode exhibits a stable linear response of the open circuit potential to the logarithm of the fluoride ion concentration in PC solutions over a range of 10-4-10-2 mol dm-3. The lower and upper limits of the linear response were interpreted in terms of the solubility and the formation of a silver fluoride complex. The use of this electrode of the second kind is suitable for the analysis of fluoride ions in organic solutions and is a promising concept for the development of ISEs for the detection of ions in organic solutions under highly restrictive conditions.

Ion exchange in solute transport has traditionally been estimated, using constant values. The exchange coefficient relating the exchange between an ion in solution and one on the soil or solid phase is treated like an equilibrium constant. Concentrations of ions in solution are corrected for ionic strength of the solution by applying activity coefficients and using the activity of the ion but there is no way to correct for the “surface phase activity”. Several have provided correction factors such a Vaneslow (1932), Krishnamoorthy and Overstreet (Soil Sci 69:41, 1950) and Gaines and Thomas (1953) to explain the distribution of ions in systems. This paper identifies a further addition to the Gaines-Thomas equation. It is additionally proposed that it is possible to determine exchange coefficients as functions of solution characteristics and variable retardation factors that are a function of the ion solution concentration. These strategies are an attempt to account for surface phase activity and the impact of multiple ions in solution.

Electrogenerated chemiluminescence (ECL) from a solution of ruthenium (II) tris(2,2'-bipyridyl) Ru(bpy)/sub 3//sup 2+/ generated at an interdigitated microelectrode array (IDA) and detected with an on-chip integrated silicon photodiode is reported. This novel approach combines the analytical properties of IDAs with the high sensitivity and selectivity of ECL reactions, together with the convenience in using an integrated photometric device.

This paper reports the design, fabrication and testing of a microchip wherein interdigitated microelectrode arrays (IMEA) were integrated with bipolar semiconductor photodiode array (PDA) chip to fabricate a highly compact embodiment for on-chip handling of solutions and electrochemiluminescence (ECL) detection. A 12 x 12 micro array of photodiodes, each coupled with an interdigitated microelectrode array (IMEA), an array of current amplifiers, and a photodiode element-addressing circuit were integrated into a single 2 x 2 cm² IC chip. Each photodiode had dimensions of 300 x 300 μm² and the photodiode-to-photodiode distance was 100 μm. The chip was successfully applied to the on-chip quantification of electro-chemiluminescing probe-labeled single stranded oligonucleotides. The minimum detectable limit at signal/noise ≥ 3 was found to be 5 x 10⁻¹⁴ moles of oligonucleotides with a sample volume as low as 5 microl (i.e., 10 fmole/μl). The attractive features of the developed IMEA-PDA microchip are that a plurality of samples can be analyzed simultaneously using a chip and that for a given sample the data can be averaged from values obtained from multiple, individually addressed pixels. These in turn bring in speed and statistical confidence in analysis. The IMEA-PDA microchip system has the potential to be used as a versatile and highly compact chemical analysis tool for chemical sensing and metrology applications.

The thermal effects of mixing of aqueous calcium chloride with sodium citrate and ethylenedi-aminetetraacetate in the absence and presence of sodium oxalate have been measured at 25°C. The thermal effects of dilution of aqueous calcium chloride solutions were determined. The thermal effects of calcium oxalate precipitation and formation of calcium complexes with citrate and ethylenediaminetetraacetate ions were calculated. The 1% solution of sodium citrate inhibited the formation of CaC2O4 (s); in a 1% solution of sodium ethylenediaminetetraacetate with [Ca2+][C2O 4 2− ] > 10−5, the endothermal formation of the [CaEdta]2− complex quickly changed to exothermal precipitation. The 3 and 5% solutions of complexons showed a pronounced inhibiting effect on the formation of urinary stones even when the concentration of calcium and oxalate ions in solution exceeded the product of solubility of CaC2O4 by four and more orders of magnitude.

Limitations of Nickel Hypophosphite Electroless Nickel Processes

A small-volume voltammetric detection of 4-aminophenol (PAP) has been developed using an interdigitated array (IDA) microelectrode cell in order to apply the IDA to electrochemical enzyme immunoassay. The signal of PAP at the IDA was steady state, and its magnitude was amplified compared with that of the usual single electrode due to redox cycling of PAP between the two finger sets of the IDA. A linear relationship between PAP concentration and cathodic limiting current was obtained from 1 to 1000 microM, reproducibly. The minimum sample volume in the measurement was reduced to 800 nL. High sample throughput of less than 1-min detection time per sample was achieved on 2-10-microL PAP samples. This IDA cell was applied to the electrochemical enzyme immunoassay of mouse IgG. Alkaline phosphatase was used as the enzyme label. The mouse IgG concentration was evaluated by detecting the concentration of PAP, which is the product of enzymatic reaction of the substrate, 4-aminophenyl phosphate (PAPP). Anti-mouse IgG was covalently immobilized on the glass surface of the small-volume immunowells by carbodiimide coupling. The assay range was 10-1000 ng/mL using 10-microL sample and 20-microL substrate solutions.