Potentiometric Detection Research Articles

Rapid DNA electrochemical biosensing platform for label-free potentiometric detection of DNA hybridization

This paper described a novel electrochemical DNA biosensor for rapid specific detection of nucleic acids based on the sulfonated polyaniline (SPAN) nanofibre and cysteamine-capped gold nanoparticle (CA-G(NP)) layer-by-layer films. A precursor film of 3-mercaptopropionic acid (MPA) was firstly self-assembled on the Au electrode surface. CA-G(NP) was covalently deposited on the Au/MPA electrode to obtain a stable substrate. SPAN nanofibre and CA-G(NP) were alternately layer-by-layer assembled on the stable substrate by electrostatic force. Cyclic voltammetry was used to monitor the consecutive growth of the multilayer films by utilizing [Fe(CN)(6)](3-/4-) as the redox indicator. The (CA-G(NP)/SPAN)(n) films showed satisfactory ability of electron transfer and excellent redox activity in neutral media. Negatively charged probe ssDNA was immobilized on the outer layer of the multilayer film (CA-G(NP)) through electrostatic affinity. Chronopotentiometry and electrochemical impedance spectroscopy were employed to obtain the direct electrochemical readout for probe ssDNA immobilization and hybridization using [Fe(CN)(6)](3-/4-) in solution as the mediator. While electrochemical impedance spectroscopy led to the characterization of the electron-transfer resistance at the electrode, chronopotentiometry provided the total resistance at the interfaces of the modified electrodes. A good correlation between the total electrode resistances and the electron-transfer resistances at the conducting supports was found. Chronopotentiometry was suggested as a rapid transduction means (a few seconds). Based on the (CA-G(NP)/SPAN)(n) films, the target DNA with 20-base could be detected up to 2.13x10(-13)mol/L, and the feasibility for the detection of base-mismatched DNA was also demonstrated.

Polypyrrole-based potentiometric phosphate biosensor

A phosphate biosensor based on potentiometric detection mode is described. Purine nucleoside phosphorylase (PNP) and xanthine oxidase (XOD) were immobilised into polypyrrole films for potentiometric measurement of phosphate in 0.05 M barbitone buffer (pH 7.8) which contain 10 mM inosine. A minimum detectable amount of 1.0 μM phosphate and a linear concentration range of 5–25 μM were achieved enabling sensitive potentiometric detection and a wide linear concentration range. The presence of uric and ascorbic acids had the least effect on the performance of the PPy–PNP–XOD–Fe(CN) 6 4− biosensor and therefore will not have any effect on phosphate measurement at levels normally present in water.

Determination of inorganic anions in mushrooms by ion chromatography with potentiometric detection

A simple method for determination of common inorganic anions in mushroom samples has been developed by using suppressed ion chromatography with a pH detection unit. The detection unit which was constructed in such a way that practically no additional dispersion occurred consisted of a flow-through quinhydrone pH sensor and a small reference electrode. Chromatographic separation was performed in the order F−, Cl−, NO2−, Br−, PO43−, ClO3−, NO3−, and SO42−, at room temperature by using Ion Pac AS 9-HC anion exchange column. Anion extracts from dried mushroom samples at room temperature were homogenized and filtered before injection. Under optimized analytical conditions, the detection limits of the method were between 2 × 10−6 and 3 × 10−4 M, depending on the anion studied. The results showed that the concentrations of fluoride and bromide in all mushroom samples were below their limit of detection. Nitrite was found to be the lowest abundant ion, while the most abundant ion was sulfate in all the mushroom samples studied.

Potentiometric Detection of DNA Hybridization using Enzyme-Induced Metallization and a Silver Ion Selective Electrode

Here, we report on a highly sensitive potentiometric detection of DNA hybridization. The new assay uses a low-volume solid-contact silver ion-selective electrode (Ag(+)-ISE) to monitor the depletion of silver ions induced by the biocatalytic reaction of the alkaline-phosphatase enzyme tag. The resultant potential change of the Ag(+)-ISE, thus, serves as the hybridization signal. Factors affecting the potentiometric hybridization response have been optimized to offer a detection limit of 50 fM (0.2 amol) DNA target. The new potentiometric assay was applied successfully to the monitoring of the 16S rRNA of E. coli pathogenic bacteria to achieve a low detection limit of 10 CFU in the 4 microL sample. Such potentiometric transduction of biocatalytically induced metallization processes holds great promise for monitoring various bioaffinity assays involving common enzyme tags.

Single interface flow system with potentiometric detection for the determination of nitrate in water and vegetables

In this work a single interface flow system (SIFA) with potentiometric detection was for the first time implemented and applied to the determination of nitrate in waters and plant extracts. The analytical potential of the SIFA system was exploited not only to transport the sample towards detection but also to carry out, in a reproducible and automated way, the tasks associated with sample pre-treatment, namely ionic strength, pH adjustment and interfering species suppression. The advantageous aspects of combining a SIFA system with potentiometry with enhanced simplicity, ease of implementation and automation were further discussed and emphasised. The obtained results showed relative deviations lower than 5%, for both types of samples, with sampling rates of about 40 h −1. In addition, an innovative and straightforward process for constructing plastic membrane ion selective electrodes with a tubular configuration able to be coupled to flow-based analytical systems is also proposed. The developed approach, consisting of assembling the electrode inside a flow tubing connector is very simple to implement, robust, particularly adequate to be combined with flow methodologies and maintains all dynamic and analytical characteristics exhibited by previous assembling processes.

Batch and hydrodynamic monitoring of vitamin C using novel periodate selective sensors based on a newly synthesized Ni(II)-Schiff bases complexes as a neutral receptors

A highly selective membrane electrodes based on a two newly synthesized nickel (II) Schiff bases, [NiL 1] and [NiL 2] where L 1 and L 2 are N,N/bis(salicylaldehyde)4,5-dimethyl-1,2-phenylenediamine (H 2L 1) and N,N/bis(salicylaldehyde)4,5-dichloro-1,2-phenylenediamine (H 2L 2) were used as a neutral carrier ionophores for static and hydrodynamic potentiometric mode of operations for the determination of periodate. Under static mode of operation, the sensors displayed a near-Nernstian slope of −66.1 ± 0.8 and −59.9 ± 1.1 mV decade −1 of activity and detection limits to 5.2 × 10 −6 and 7.3 × 10 −6 mol L −1 for the sensors based on [NiL 1] and [NiL 2], respectively. Under hydrodynamic mode of operation (FIA), the slope of the calibration plot, limit of detection, and working linear range were −71.1 mVdecade −1 of activity, 7.3 × 10 −6 and 1.0 × 10 −5 to 1.0 × 10 −3 mol L −1, respectively. The response time of the sensors in whole concentration ranges was very short (<10 s). The response of the sensors was independent on the pH range of 3–8. A tubular version was further developed and coupled to a flow injection system for ascorbic acid (AA) determination in beverages and pharmaceutical preparations. This approach was achieved by selecting a 50-cm reactor and an overall flow of 3 mL min −1, and injecting volume 100 μL of AA standards in a 1.0 × 10 −4 mol L −1 IO 4 − solution. Under these conditions, a linearity range of 2–13 μg mL −1, with a slope of 4.97 mV (mg/L) −1 ( r 2 = 0.9995), detection limit 0.9 mg L −1 and a reproducibility of ±1.1 mV ( n = 5) was recorded. This simple and inexpensive flow injection analysis manifold, with a good potentiometric detector, enabled the analysis of ∼50 samples h −1 without requiring pretreatment procedures. An average recovery of 98.8% and a mean standard deviation of 1.3% were obtained.

Comparison Between Potentiometric and Stripping Voltammetric Detection of Trace Metals: Measurements of Cadmium and Lead in the Presence of Thalium, Indium, and Tin

Recent advances in ion-selective electrodes have pushed the detection limits of direct potentiometry to the nanomolar concentration range. Here we present a direct comparison of the sensitivity and selectivity of potentiometric and stripping-voltammetric measurements of cadmium and lead. While both techniques offer a similar sensitivity, the potentiometric method offers higher selectivity in the presence of excess of metal ions (e.g., thallium, tin) that commonly interfere in the stripping-voltammetric operation. Because of the complementary nature of the potentiometric and stripping-voltammetric methods, it is recommended that these techniques will be selected based on the specific analytical problem or used in parallel to provide additional analytical information.

Comparison of enzyme immobilisation methods for potentiometric phosphate biosensors

The development of two phosphate biosensors is described and compared for potentiometric detection of phosphate. Purine nucleoside phosphorylase (PNP) and xanthine oxidase (XOD) were co-immobilised by chemical cross-linking with glutaraldehyde (GLA) and bovine serum albumin (BSA), and via entrapment into polypyrrole (PPy) films by galvanostatic polymerisation. The BSA-GLA film was made with 4.5% v/v GLA and 6.8% w/v BSA with a drying time of 30min, while polypyrrole entrapment was achieved with 0.5M pyrrole by using a polymerisation time of 200s. A mole ratio of 1:8 (6.2U/mL XOD: 49.6U/mL PNP) was used for both methods of enzyme immobilisation. Sensitive potentiometric measurements obtained for phosphate with the BSA-GLA-PNP-XOD biosensor were compared with those of PPy-PNP-XOD-Fe(CN)64− biosensor. A minimum detectable concentration of 0.1mg/L phosphate and a linear concentration range of 0.5–2.5mg/L were achieved with the PPy-PNP-XOD-Fe(CN)64− biosensor. In comparison, a minimum detectable concentration of 2mg/L and a linear concentration range of 4–12mg/L were achieved with the BSA-GLA immobilisation. The presence of uric and ascorbic acids had the least effect on the performance of the PPy-PNP-XOD-Fe(CN)64− biosensor, but will not have any effect on phosphate measurement with both biosensors at levels normally present in water.

Potentiometric VOC detection in air using 8YSZ-based oxygen sensor modified with SmFeO 3 catalytic layer

Potentiometric oxygen sensor was fabricated and applied to detect several volatile organic compounds (VOCs; acetic acid, methylethylketone (MEK), ethanol, benzene, toluene, o- and p-xylene) at sub-ppm levels in the temperatures range of 400–500 °C. The electromotive force (EMF) linearly changed with the logarithm of VOC concentration. Especially for ethanol and MEK, the sensitivity and EMF at 1 ppm were distinctly lowered for the sensor with the SmFeO 3 coated Pt working electrode. It seems that ethanol and MEK were more easily oxidized on the SmFeO 3 surface than the other VOCs. A discriminative detection of ethanol and MEK apart from the others could be achieved with the combination of two types of the sensors, Pt|8YSZ|Pt(ref.) and SmFeO 3/Pt|8YSZ|Pt(ref.).

Silacrown modified xerogels as functional hybrid materials for carbon composite electrodes

The entrapment of the ionophore 1,1-dimethylsila-17-crown-6 (DMS17C6) in a polysiloxane matrix derived from the 3-(trimethoxysilyl) propyl methacrylate (MAPTS) and tetramethoxysilane (TMOS) alkoxysilanes, yields a functional hybrid material suitable for the development of bulk-modified electrodes. The resulting sensors exhibit a long-time stability, robustness and a suitable electroanalytical performance in the potentiometric detection of alkali metal ions (i.e. Li+, Na+ and K+) in aqueous solution. Due to their cross-sensitivity property, these DMS17C6-based sensors exhibit a potentiometric response towards all the tested cations, but they show a higher selectivity towards K+ than that observed for analogous 18C6-based sensors. L’inclusion de l’ionophore 1,1-diméthylsila-17-couronne-6 (DMS17C6) dans une matrice de polysiloxane preparée au départ des alkoxysilanes : 3-(triméthoxysilyl)propyl méthacrylate (MAPTS) et tétraméthoxysilane (TMOS), conduit à la formation d’un matériau hybride fonctionnel d’intérêt pour le développement des électrodes ionosélectives. Les capteurs qui en résultent sont robustes en montrant une bonne stabilité à long terme, et une réponse électroanalytique appropriée pour la détection potentiométrique des ions alcalins (c’est-à-dire, Li+, Na+ et K+) dans des solutions aqueuses. En raison de leur propriété de sensibilité croisée, ces capteurs à base du DMS17C6 montrent une réponse potentiométrique adéquate vers tous les cations examinés, mais elles montrent une sélectivité plus élevée vers K+ que des capteurs similaires basés dans l’ionophore 18-couronne-6 (18C6).

Organically nanoporous silica gel based on carbon paste electrode for potentiometric detection of trace Cr(III)

A new ion-selective electrode (ISE) for the detection of trace chromium(III) was designed by using 2-acetylpyridine and nanoporous silica gel (APNSG)-functionalized carbon paste electrode (CPE). The presence of APNSG acted as not only a paste binder, but also a reactive material. With 7.5 wt% APNSG proportions, the developed electrode exhibited wide dynamic range of 1.0 × 10 −8 to 1.0 × 10 −3 M toward Cr(III) with a detection limit of 8.0 × 10 −9 M and a Nernstian slope of 19.8 ± 0.2 mV decade −1. The as-prepared electrode displayed rapid response (∼55 s), long-time stability, and high sensitivity. Moreover, the potentiometric responses could be carried out with wide pH range of 1.5–5.0. In addition, the content of Cr(III) in food samples, e.g. coffee and tea leaves, has been assayed by the developed electrode, atomic absorption spectrophotometer (AAS) and atomic emission spectrometer (ICP-AES), respectively, and consistent results were obtained. Importantly, the response mechanism of the proposed electrode was investigated by using AC impedance and UV–vis spectroscopy.

Determination of nitrogen dioxide, sulfur dioxide, ozone, and ammonia in ambient air using the passive sampling method associated with ion chromatographic and potentiometric analyses.

Concentrations of nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), and ammonia (NH3) were determined in the ambient air of Al-Ain city over a year using the passive sampling method associated with ion chromatographic and potentiometric detections. IVL samplers were used for collecting nitrogen and sulfur dioxides whereas Ogawa samplers were used for collecting ozone and ammonia. Five sites representing the industrial, traffic, commercial, residential, and background regions of the city were monitored in the course of this investigation. Year average concentrations of ≤59.26, 15.15, 17.03, and 11.88 μg/m3 were obtained for NO2, SO2, O3, and NH3, respectively. These values are lower than the maxima recommended for ambient air quality standards by the local environmental agency and the world health organization. Results obtained were correlated with the three meteorological parameters: humidity, wind speed, and temperature recorded during the same period of time using the paired t test, probability p values, and correlation coefficients. Humidity and wind speed showed insignificant effects on NO2, SO2, O3, and NH3 concentrations at 95% confidence level. Temperature showed insignificant effects on the concentrations of NO2 and NH3 while significant effects on SO2 and O3 were observed. Nonlinear correlations (R 2 ≤ 0.722) were obtained for the changes in measured concentrations with changes in the three meteorological parameters. Passive samplers were shown to be not only precise (RSD ≤ 13.57) but also of low cost, low technical demand, and expediency in monitoring different locations.

Determination of ascorbic acid by polypyrrole potentiometric detector in ion chromatography

A potentiometric detector, based on electrodeposition of polypyrrole onto Pt electrode, was investigated in this study. The chromatographic performance of the PPy detector was investigated in ion chromatography. The resulting PPy detector exhibited good performance for AA determination with a wide linear range (1.0 × 10 −6 to 1.0 × 10 −2 M), a highly reproducible response (R.S.D. of 2.45%), without any interference and long-term stability. The calculated detection limit was 7.0 × 10 −5 mM at 3 σ. The calibration results showed good Nernstian behavior and also satisfactory low detection limit. In order to verify the reliability of the PPy detector, it was applied to the determination of AA in pharmaceutical samples. The results were satisfactory and agreed closely with the manufacturers’ stated contents. The PPy electrode can be used as an alternative novel potentiometric detector material for determination of AA in standards and pharmaceutical samples.

Tb3+-enhanced Potentiometric Detection of Single Nucleotide Polymorphism by Field Effect Transistors

Abstract The use of Tb3+ as a center ion and media to introduce more exogenously negative charges onto double-stranded DNA (dsDNA), can greatly enhance potentiometric signals produced by the shift of gate voltage of field effect transisitor (FET). Furthermore, different affinities of Tb3+ to normal and mismatched dsDNAs amplified the signal difference between their detections, which can improve the discrimination of single nucleotide polymorphism.

Potentiometric DO detection in water by ceramic sensor based on sub-micron RuO2 sensing electrode

An alumina sensor using sub-micron RuO2 sensing electrode (SE) was fabricated and examined for potentiometric dissolved oxygen (DO) detection in water at a temperature range of 9–35 °C. The electromotive force (emf) response at these temperatures was linear to the logarithm of DO concentration in the range from 0.6 to 8.0 ppm (log[O2], −4.71 to −3.59). RuO2-SE displays a Nernstian slope of −41 mV per decade at pH 8.0. It was also found that the response/recovery time to DO changes were sluggish as the water temperature cools down. Response time T90 to DO changes increased from 8 min at a temperature of 23 °C to about 30 min at a temperature of 9 °C. The proton conductivity of hydrous RuO2 appears to be due to the dissociative adsorption of water and the formation of acidic OH groups in Ru (III,IV) cluster ions. In strong alkaline solutions, the sensor’s emf exhibited a mixed potential of fast and slow electrochemical reactions involving DO, RuO42− and OH− ions. The results also revealed that as pH of the solution increases to pH 10.0–13.0, the response/recovery rate becomes faster, stabilizing more or less quickly depending upon the solution alkalinity. Scanning electron microscopy, energy dispersive X-ray-analysis and impedance spectroscopy techniques were used to examine respectively the morphology, crystalline structure and electrochemical behaviour of sub-micron RuO2 oxides.

Potentiometric enzyme immunoassay using miniaturized anion-selective electrodes for detection

An enzyme-linked immunosorbent assay (ELISA) for prostate specific antigen (PSA) detection in human serum was developed based on the potentiometric detection of 6,8-difluoro-4-methylumbelliferone (DiFMU). The assays were carried out in anti-human PSA capture antibody modified microtiter plates (150 microL volume). After incubation in the PSA-containing serum samples, beta-galactosidase-labeled PSA tracer antibody was added. The beta-galactosidase label catalyzed the hydrolysis of 6,8-difluoro-4-methylumbelliferyl-beta-D-galactopyranoside (DiFMUG) and the resulting DiFMU(-) anion was detected by potentiometric microelectrodes with anion-exchanger membrane. The selectivity of the anion-exchanger electrode is governed by the lipophilicity of the anions in the sample. Since DiFMU(-) is much more lipophilic (log P = 1.83) than any of the inorganic anions normally present in the working buffers and occurs in its anionic form at the physiological pH (pK(a) = 4.19), it was chosen as the species to be detected. The potentiometric ELISA-based method detects PSA in serum with a linear concentration range of 0.1-50 ng/mL. These results confirm the applicability of potentiometric detection in diagnostic PSA assays. Owing to simple methodology and low cost, potentiometric immunoassays seem to offer a feasible alternative to the development of in vitro diagnostic platforms.

Unique potentiometric detection systems for HPLC determination of some steroids in human urine

Isocratic HPLC with potentiometric detection is used for the determination of some 17-ketosteroids (17-KS), e.g., androsterone, dehydroepiandrosterone and estrone, and their respective sulfated conjugates (17-KSS). Glassy carbon or composite electrodes containing a mixture of graphite and poly(vinyl chloride), PVC, were used as substrate electrodes. These substrates were covered either by montmorillonite or potassium tetrakis(p-chlorophenyl) borate containing PVC-based rubber phase membranes. The neutral 17-KS compounds were derivatized with Girard's reagent P (GP) to obtain cationic pyridinium acetohydrazones prior to the HPLC/potentiometric detection assay. No side reactions were observed, and the GP itself was not interfering. The method yielded accurate and reproducible results and was applicable to samples containing down to micromolar concentrations. Next, the 17-KSS compounds, acting as anionic charged molecules, were determined directly in human urine samples with the HPLC/potentiometry combination without preliminary derivatization. For this purpose, a new anion-sensitive potentiometric electrode was developed using a macrocyclic polyamine containing, PVC-based, rubber phase membrane. The three 17-KSS compounds were also determined accurately down to micromolar concentrations. Especially, the main androgen metabolites as dehydroepiandrosterone sulfate and androsterone sulfate could be selectively determined with a developed potentiometric sensor in human urine samples without time-consuming cleanup and preconcentration step.

Microtitrimetric determination of a drug content of pharmaceuticals containing olanzapine in non-aqueous medium

Two simple, rapid, reliable and cost-effective methods based on titrimetry in non-aqueous medium are described for the determination of olanzapine in pharmaceuticals. In these methods, the drug dissolved in the glacial acetic acid was titrated with the acetous perchloric acid with visual and potentiometric end point detection, crystal violet being used as the indicator for visual titration. The methods are applicable over 1-15 mg range of olanzapine. The procedures were applied to determine olanzapine in pharmaceutical products and the results were found to be in a good agreement with those obtained by the reference method. Associated pharmaceutical materials did not interfere. The precision results, expressed by inter-day and intra-day relative standard deviation values, were satisfactory, higher than 2%. The accuracy was satisfactory as well. The methods proved to be suitable for the analysis of olanzapine in bulk drug and in tablets. The accuracy and reliability of the methods were further ascertained by recovery studies via a standard addition technique with percent recoveries in the range 97.51-103.7% with a standard deviation of less than 2%.

Nitrogen speciation by microstill flow injection analysis

A sequential determination of ammonia, nitrite, and nitrate has been carried out using a flow injection manifold incorporating a Microstill. The nitrogen speciation method has been designed using inorganic acid and base reagents, thus avoiding colorimetric reactions whose associated reagents and products are environmentally unacceptable. The robust manifold requires just three valves to switch measurement conditions for each species. UV irradiation was selected for nitrate reduction and gave acceptable resolution of nitrate and nitrite ions. In solutions containing comparable concentrations of both species, reduction of nitrate by UV irradiation gives a systematic error for nitrate due to nitrite interference at the 95% confidence level, nitrite being partially oxidised to nitrate during sample processing. At 98% confidence the error was not significant. A glass microelectrode provided potentiometric detection in an ammonium chloride post-still collector stream. Ammonium chloride provided adequate baseline recovery when switching from acidic to basic distillation conditions, although resulting in an increase in detection limits over those found for a single analyte by the Microstill technique. The final speciation procedure gave working ranges of 0.03-10 mg/L for ammonia-N, 0.05-5 mg/L for nitrite-N and 0.1-10 mg/L for nitrate-N. The three N species were determined in 12 min for each water sample. The system has had limited trials in river waters containing ammonia and nitrate. Good precision and recoveries were obtained for the two species in the samples tested.

Hydrophobicity‐aided potentiometric detection of catecholamines, beta‐agonists, and beta‐blockers in a mixed‐solvent capillary electrophoresis system

A series of cationic drug-like substances with distinct basicity, hydrogen-bonding ability, and hydrophobicity, including three catecholamines, two beta-agonists, and thirteen beta-blockers, was successfully detected in a capillary electrophoresis system using an end-capillary coupled potentiometric sensor consisting of a PVC-based liquid membrane deposited directly on a 100 mum diameter copper rod. The electrophoretic separation was performed on a 72 cm x 75 microm id uncoated fused-silica capillary with an acidic background electrolyte containing phosphoric acid in a water-acetonitrile mixture, pH* 2.8. Samples were injected electrokinetically at 5.0 kV for 10 s and a running voltage of 19.5 kV was applied. Excluding the bufuralol/practolol pair, baseline separation of all substances was achieved in the developed CE system within 9 minutes. A linear relationship (R(2) 0.8752) between the sensitivity of the applied potentiometric detector and the parameter log P characterising the hydrophobicity of the analytes was demonstrated. The best observable limits of detection (LODs) were obtained for the highly hydrophobic substances, i. e. bufuralol (8.10 x 10(-8) M injected concentration, S/N = 3), propranolol, alprenolol, and clenbuterol (ca. 1.10 x 10(-7) M). In the case of hydrophilic catecholamines and carbuterol their LODs with potentiometric detection were lowered by a factor of almost one thousand, reaching a value of 6.6 x 10(-5) M.