Polymeric Membrane Electrodes Research Articles

A Polymeric Liquid Membrane Electrode Responsive to 3,3′,5,5′-Tetramethylbenzidine Oxidation for Sensitive Peroxidase/Peroxidase Mimetic-Based Potentiometric Biosensing

The oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) has great utility in bioanalysis such as peroxidase/peroxidase mimetic-based biosensing. In this paper, the behaviors of TMB oxidation intermediates/products in liquid/liquid biphasic systems have been investigated for the first time. The free radical, charge transfer complex, and diimine species generated by TMB oxidation are all positively charged under acidic and near-neutral conditions. Electron paramagnetic resonance and visible absorbance spectroscopy data demonstrate that these cationic species can be effectively transferred from an aqueous phase into a water-immiscible liquid phase functionalized by an appropriate cation exchanger. Accordingly, sensitive potential responses of TMB oxidation have been obtained on a cation exchanger-doped polymeric liquid membrane electrode under mildly acidic and near-neutral conditions. By using the membrane electrode responsive to TMB oxidations, two sensitive potentiometric biosensing schemes including the peroxidase-labeled sandwich immunoassay and G-quadruplex DNAzyme-based DNA hybridization assay have been developed. The obtained detection limits for the target antigen and DNA are 0.02 ng/mL and 0.1 nM, respectively. Coupled with other advantages such as low cost, high reliability, and ease of miniaturization and integration, the proposed polymeric liquid membrane electrode holds great promise as a facile and efficient transducer for TMB oxidation and related biosensing applications.

Electrochemical Determination of Perchlorate Ion By Polymeric Membrane and Coated Graphite Electrodes Based on Zinc Complexes of Macrocyclic Ligands

The quick determination of trace quantities of ionic species, by simple methods, is of special interest in analytical chemistry. Ion selective electrodes based on solvent polymeric membranes with incorporation of ion carriers are shown to be very useful tools for chemical, clinical and environmental analyses as well as in process monitoring [1-3]. In addition to the cation-selective electrodes, recently the design and synthesis of sensory molecules for anion-selective electrodes has become a challenging subject [4]. For a truly anion-selective electrode, a strong interaction between the ionophore and the anion is required in order to complex anion in a selective fashion. Potentiometric response of the membranes doped with these complexes is believed to be based on the coordination of analyte anion with carrier molecule.The electrode characteristics and selectivities of PVC-based perchlorate selective coated graphite electrode (CGE) and polymeric membrane electrode (PME) incorporating the synthesized zinc complexes of 6,7:13,14-Dibenzo-2,4,9,11-tetramethyl-1,5,8,12-tetraazacyclotetradecane-1,4,6,8,11,13-hexaene (I1) and 6,7:13,14-Dibenzo-2,4,9,11-tetramethyl-1,5,8,12-tetramethylacrylate-1,5,8,12-tetraazacyclotetradecane-6,13-diene (I2) are reported here. Several membranes having different compositions of PVC, plasticizers, ionic additives and ionophores were fabricated and the best response was observed for the membrane having composition I2: PVC: BA: HTAB in the ratio of 7: 32: 59: 2 (w/w; mg). The PME shows good performance characteristics in terms of detection limit of 5.4 × 10− 7 mol L− 1, working concentration range of 8.3 × 10− 7 to 1.0 × 10− 2 mol L− 1 and slope 58.7 ± 0.3 mV decade− 1 of activity. Thus the CGE with same membrane composition was prepared and its potentiometric response characteristics were compared. The electrode exhibits Nernstian slope for perchlorate ions over wide concentration ranges i.e. 8.3 × 10-7 to 1.0 × 10-2 mol L-1 (with PME) and 1.0 × 10-7 to 1.0 × 10-2 mol L-1(with CGE) and response time of 12 s and 9 s for PME and CGE respectively. The proposed electrodes generated constant potentials in the pH range of 3.0-8.0 for PME and 2.5-9.0 for CGE. The high selectivity of CGE for perchlorate ions permits its use in the determination of perchlorate ions in various samples such as water and human urine samples.Fig. 1. (a) Structure of zinc complex of 6,7:13,14-Dibenzo-2,4,9,11-tetramethyl-1,5,8,12-tetraazacyclotetradecane-1,4,6,8,11,13-hexaene (I1) (b) Structure of zinc complex of 6,7:13,14-Dibenzo-2,4,9,11-tetramethyl-1,5,8,12-tetramethylacrylate-1,5,8,12-tetraaza-cyclotetradecane-6,13-diene (I2).Table 1. Response characteristics of the perchlorate ion-selective electrodes based on PME and CGEPropertiesPotentiometric ResponsePMECGEOptimized membrane composition (w/w; mg)(I2: PVC: BA : HTAB) ≡ (7: 32: 59: 2)(I2: PVC: BA : HTAB) ≡ (7: 32: 59: 2)Working concentration range ( mol L-1)8.3 ´ 10-7 -1.0 ´ 10-2 1.0 ´ 10-7–1.0 ´ 10-2 Detection limit ( mol L-1)5.4 ´ 10-7 8.4 ´ 10-8 Slope (mV decade-1 of activity)58.7 ± 0.359.3 ± 0.2Response time (s)129Life span30 days65 dayspH range3.0 - 8.02.5 - 9.0

Determination of Er3+ Ion at Nano Level Based on Newly Synthesized Schiff Base As a Neutral Carrier By Coated Graphite Electrode

The rare earth elements (REEs) are mainly of two series Lanthanides and Actinides. Despite of their name REEs are not so rare in environment, they widely distributed in throughout the earth’s crust in low concentration. The REEs have significant industrial application as competitive to transition elements and wide application have been found in bioinorganic, inorganic chemistry. Erbium is mainly used as laser beams to resurfacing skin, transdermal drug delivery, transdermal peptide delivery, skin vaccination and enhances the RNA delivery. It is estimated that the erbium concentration of the earth’s crust reaches 24 ppm. The commercial sources of erbium are monazite and bastnasite. Even though the conclusion of the investigators, the rare earth elements are considered as low acute toxicity rating, these causes several problems to living species. Due to their enhanced discharge, toxic properties and other adverse effects, determination of erbium is essential in a variety of environmental samples.A number of instrumental techniques such as second order derivative spectrophotometry, third-derivative spectrophotometry, X-ray fluorescence, graphite furnace atomic spectrometry techniques, inductively coupled plasma mass spectrometry, rutherford backscattering spectrometry and spectrophotometric determination are available for its estimation. These methods provide accurate determination of erbium content but involve large infrastructure backup and support of expertise. We found ion-selective electrode to overcome these problems. Ion-selective electrodes are electrochemical ideal sensors in many respects for use in the analysis of industrial and environmental samples.Plasticized membranes using N-(-3-((thiazol-2-ylimino)methyl)benzylidene)thiazol-2-amine (S1) and 5-((-3-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)-benzylidene)amino)-1,3,4-thiadiazole-2-thiol (S2) have been prepared and explored as Er3+ selective electrodes. Effect of various plasticizers viz. dibutylphthalate (DBP), tri-n-butylphosphate (TBP), dioctylphthalate (DOP), acetophenone (AP), 1-chloronapthalene (1-CN), o-nitrophenyloctylether (o-NPOE), and anion excluders viz. sodium tetraphenylborate (NaTPB) and potassium tetrakis-p-(chlorophenyl)borate (KTpClPB) was studied in detail and improved performance was observed. Optimum performance was observed for the membrane electrode having a composition of S2: PVC: o-NPOE: KTpClPB in the ratio of 4: 38: 55: 3 (w/w, mg). The performance of the polymeric membrane electrode (PME) based on S2 was compared with coated graphite electrode (CGE). The electrodes exhibit Nernstian slope for Er (III) ions with limit of detection of 5.4 × 10-8 mol L−1 for PME and 6.1 × 10-9 mol L−1 for CGE. The response time for PME and CGE was found to be 12 s and 9 s respectively. The potentiometric responses are independent of the pH of the test solution in the pH range 4.0-9.0 for PME and 3.0-9.5 for CGE. The CGE could be used for a period of 7 weeks. The practical utility of the CGE has been demonstrated by its usage as an indicator electrode in potentiometric titration of EDTA with Er (III) solution and determination of F- ion in mouthwash solution. The proposed electrode was also successfully applied to the determination of Er3+in water, binary mixtures. Table 1. Response characteristics of Er3+ ion selective electrodes based on PME and CGE. PropertiesElectrode ResponsePMECGEWorking concentration range (mol L-1)7.9 × 10-8 - 1.0 × 10-1 9.4 × 10-9 - 1.0 × 10-1 Detection limit (mol L-1)5.4 × 10-8 6.1 × 10-9 Slope (mV decade-1 of activity)19.8 ± 0.419.6 ± 0.3Response time (s)129pH range4.0-9.03.0-9.5Fig. 1. Structure of ligands N-(-3-((thiazol-2-ylimino)methyl)benzylidene)thiazol-2-amine (S1) and 5-((-3-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)-benzylidene)amino)-1,3,4-thiadiazole-2-thiol (S2)

Electrochemical determination of perchlorate ion by polymeric membrane and coated graphite electrodes based on zinc complexes of macrocyclic ligands

The electrode characteristics and selectivities of PVC-based perchlorate selective coated graphite electrode (CGE) and polymeric membrane electrode (PME) incorporating the synthesized zinc complexes of 6,7:13,14-dibenzo-2,4,9,11-tetramethyl-1,5,8,12-tetraazacyclotetradecane-1,4,6,8,11,13-hexaene (I1) and 6,7:13,14-dibenzo-2,4,9,11-tetramethyl-1,5,8,12-tetramethylacrylate-1,5,8,12-tetraazacyclotetradecane-6,13-diene (I2) are reported here. Several membranes having different compositions of PVC, plasticizers, ionic additives and ionophores were fabricated and the best response was observed for the membrane having composition I2:PVC:BA:HTAB in the ratio of 7:32:59:2 (w/w; mg). The response characteristics of PME based on the above mentioned membrane was also compared with CGE. The electrode exhibits a Nernstian response for perchlorate ions over wide concentration ranges i.e. 8.3×10−7 to 1.0×10−2molL−1 (with PME) and 1.0×10−7 to 1.0×10−2molL−1 (with CGE) and response time of 12s and 9s for PME and CGE, respectively. Furthermore, the electrodes generated constant potentials in the pH range of 3.0–8.0 for PME and 2.5–9.0 for CGE. The high selectivity of CGE for perchlorate ions permits its use in the determination of perchlorate ions in water and human urine samples.

Nitrite‐Selective Electrode Based On Cobalt(II) tert‐Butyl‐Salophen Ionophore

AbstractA series of polymeric nitrite‐selective electrodes containing a new lipophilic ionophore Co(II) tert‐butyl‐salophen is reported. The stability of Co(II) ionophores within a PVC‐based membrane was investigated by leaching experiments. Different membrane compositions were explored in order to reach the lowest possible limit of detection for a PVC‐based nitrite selective polymeric membrane electrode containing this ionophore. The optimal electrode showed a limit of detection of 2×10−6 M and exhibited four orders of magnitude of discrimination over nitrate, chloride and bromide. The electrodes were evaluated in undiluted human urine and attest to the robustness of the ionophore.

Construction and performance characteristics of polymeric membrane electrode and coated graphite electrode for the selective determination of Fe3 + ion

Novel Fe3+ ion-selective polymeric membrane electrodes (PMEs) were prepared using three different ionophores N-(4-(dimethylamino)benzylidene)thiazol-2-amine [L1], 5-((3-methylthiophene-2yl) methyleneamino)-1,3,4-thiadiazole-2-thiol [L2] and N-((3-methylthiophene-2yl)methylene)thiazol-2-amine [L3] and their potentiometric characteristics were discussed. Effect of various plasticizers and anion excluders was also studied in detail and improved performance was observed. The best performance was obtained for the membrane electrode having a composition of L2:PVC:o-NPOE:NaTPB as 3:38.5:56:2.5 (w/w; mg). A coated graphite electrode (CGE) was also prepared with the same composition and compared. CGE is found to perform better as it shows a wider working concentration range of 8.3×10−8–1.0×10−1molL−1, a lower detection limit of 2.3×10−8molL−1, and a near Nernstian slope of 19.5±0.4mVdecade−1 of activity with a response time of 10s. The CGE shows a shelf life of 6weeks and in view of high selectivity, it can be used to quantify Fe3+ ion in water, soil, vegetable and medicinal plants. It can also be used as an indicator electrode in potentiometric titration of EDTA with Fe3+ ion.

BEHAVIOR OF A POLYMERIC LIQUID MEMBRANE ION- SELECTIVE ELECTRODE FOR CHLORIDE ION

Chloride selective polymeric liquid membrane electrode has been developed by using Bis-(2-ethylhexyl) Sebacate (DOS) as plasticizer and 2-[5-(4-nitrophenyl) furyl]-4,5-diphenyl imidazole (FFDFIN) as ionophore. Some parameters of evaluation of the electrode are presented in this work. The constructed electrode showed fast potentiometric response to chloride ion in the concentration range from 10-6 to 10-2 mol.dm-3 with Nernstian slope of -63.43 ± 0.85 mV/decade, response time of 25 seconds and life time of 15 days.

Preparation of a new aluminum (III) selective electrode based on a hydrazone-containing benzimidazole derivative as a neutral carrier

A new aluminium (III) polymeric membrane electrode containing (E)-N′-(4-(dimetlylamino)benzylidene)-1H-benzo[d]midazobe-2-hydrazide (L) as a carrier has been prepared. The influence of membrane ingredients including ionophore, PVC, plasticizers and anionic excluders (NaTPB and KTpClPB) on the electrode response has been investigated. The best performance was obtained with a membrane composition of carrier L:DBP:PVC ratio of 1.00:65.99:33.01 (%, w/w). The sensor exhibited a Nernstian response for Al3+ ion ranging from 1.0×10−7 to 1.0×10−1M with a detection limit of 5.6×10−8M and a slope of 20.7mV/decade. It showed a relatively fast response time (10s), suitable reproducibility and stability, and good selectivity towards Al3+ ion. The prepared electrode was used as an indicator electrode in potentiometric titration of Al3+ with EDTA and in the determination of Al3+ ion in waste water and vermicelli.

Construction of a Solid Contact Polymeric Membrane Electrode for pH Measurements in Acidic Media

A recently new synthesized azo Schiff base was studied to characterize its ability as a cation carrier in PVC membrane solid contact electrode. The coated glassy carbon electrode (CGCE) prepared with the azo Schiff base showed excellent response characteristics to hydrogen ions. The electrode exhibited Nernstian slope of 58.8 mV/decade over a wide concentration range of H+ ion from 2.0 × 10−7 to 1.8 × 10−1 M. It possessed fast response time, satisfactory reproducibility, appropriate lifetime, and most importantly, good selectivity toward H+ relative to a wide variety of other cations. The cations that usually interfere in the function of pH glass electrode such as Na+ and K+ didn't show any significant interference on the response of the proposed electrode. The effect of different non-aqueous media on the response of electrode was investigated. The electrode was applied as an indicator electrode in acid-base titration. The applicability of the electrode was tested by determination of H+ in milk as a good matrix solution and the results were compared with those obtained by the glass pH-electrode.

Study of Cobalt(III) Corrole as the Neutral Ionophore for Nitrite and Nitrate Detection via Polymeric Membrane Electrodes.

Cobalt(III) 5, 10, 15-tris(4-tert-butylphenyl) corrole was synthesized and incorporated into plasticized poly(vinyl chloride) membranes and studied as a neutral carrier ionophore via potentiometry. This cobalt(III) complex has binding affinity to nitrite, and the resulting membrane electrode yields reversible and Nernstian response toward nitrite. Enhanced nitrite selectivity is observed over other anions, including lipophilic anions such as thiocyanate and perchlorate when an appropriate amount of lipophilic cationic sites are added to the membrane phase. Detection limit to nitrite is ca. 5 µM. Using tributylphosphate as the plasticizer with the cobalt(III) corrole species yields electrodes with enhanced nitrate selectivity.

Cyanex based uranyl sensitive polymeric membrane electrodes

Novel uranyl selective polymeric membrane electrodes were prepared using three different low-cost and commercially available Cyanex extractants namely, bis(2,4,4-trimethylpentyl) phosphinic acid [L1], bis(2,4,4-trimethylpentyl) monothiophosphinic acid [L2] and bis(2,4,4-trimethylpentyl) dithiophosphinic acid [L3]. Optimization and performance characteristics of the developed Cyanex based polymer membrane electrodes were determined. The influence of membrane composition (e.g., amount and type of ionic sites, as well as type of plasticizer) on potentiometric responses of the prepared membrane electrodes was studied. Optimized Cyanex-based membrane electrodes exhibited Nernstian responses for UO₂(2+) ion over wide concentration ranges with fast response times. The optimized membrane electrodes based on L1, L2 and L3 exhibited Nernstian responses towards uranyl ion with slopes of 29.4, 28.0 and 29.3 mV decade(-1), respectively. The optimized membrane electrodes based on L1-L3 showed detection limits of 8.3 × 10(-5), 3.0 × 10(-5) and 3.3 × 10(-6) mol L(-1), respectively. The selectivity studies showed that the optimized membrane electrodes exhibited high selectivity towards UO₂(2+) ion over large number of other cations. Membrane electrodes based on L3 exhibited superior potentiometric response characteristics compared to those based on L1 and L2 (e.g., widest linear range and lowest detection limit). The analytical utility of uranyl membrane electrodes formulated with Cyanex extractant L3 was demonstrated by the analysis of uranyl ion in different real samples for nuclear safeguards verification purposes. The results obtained using direct potentiometry and flow-injection methods were compared with those measured using the standard UV-visible and inductively coupled plasma spectroscopic methods.

Electroanalytical and naked eye determination of Cu2 + ion in various environmental samples using 5-amino-1,3,4-thiadiazole-2-thiol based Schiff bases

Novel polydentate Schiff bases 4-(5-mercapto-1,3,4-thiadiazol-2-ylimino)pentan-2-one (S1) and (2-(indol-3-yl)vinyl)-1,3,4-thiadiazole-2-thiol (S2) were synthesized and explored as Cu2+ selective polymeric membrane electrodes (PME) using different plasticizers and anionic excluders. The potentiometric data revealed that the PME having the membrane composition (S2: NaTPB: TBP: PVC as 4: 2: 58: 36 (w/w; mg)) is shown to have good results. Thus the coated graphite electrode (CGE) with the same composition as the best PME was also fabricated and investigated as Cu2+ selective electrode. It was found that CGE showed better response characteristics than PME with respect to low detection limit (1.2×10−8molL−1), near Nernstian slope (29.8±0.4mV decade−1 of activity), wide working concentration range (6.4×10−8–1.0×10−1molL−1), long shelf life (90days) and fast response time (9s). The CGE was used successfully as an indicator electrode for the potentiometric determination of Cu2+ ion against EDTA and also used to quantify Cu2+ ion in soil, water, medicinal plants, vegetables and edible oil samples. The Schiff base S2 is used as chemosensor for the selective determination of Cu2+ ion.

Electroanalytical performance of Cd(II) selective sensor based on PVC membranes of 5,5′‐(5,5′‐(benzo[c][1,2,5]thiadiazole‐4,7‐diyl)bis(thiophene‐5,2‐diyl))bis(N1,N1,N3,N3‐tetraphenylbenzene‐1,3‐diamine)

The construction and performance characteristics of polymeric membrane electrodes based on neutral ionophore 5,5′‐(5,5′‐(benzo[c][1,2,5]thiadiazole‐4,7‐diyl)bis(thiophene‐5,2‐diyl))bis‐(N1,N1,N3,N3‐tetraphenylbenzene‐1,3‐diamine) (L) for quantification of cadmium ions, are described. Effect of plastisizers dibutylpthalate (DBP), tri‐n‐butylphosphate (TBP), dioctylpthalate (DOP), o‐nitrophenyloctyl ether (o‐NPOE), 1‐chloronaphthalene (CN) and ionic additives sodium tetraphenylborate (NaTPB), potassium tetrakis p‐(chlorophenyl)borate (KTpClPB) was studied. Best performance was obtained with the membrane having a composition L : PVC : DBP : NaTPB ≡ 2 : 37 : 59 : 2 (w/w; mg). The membrane electrode exhibits Nernstian response in the concentration range 6.3 × 10−8 to 1.0 × 10 −1 mol L−1 with detection limit 3.6 × 10−8 mol L−1 and is not affected by H+ ions over a wide pH range 3.0–10.0. The electrode possess a fast response time of 10 s and shelf life period of 3 months. The analytical utility of the proposed electrode has demonstrated by its application in the determination of cadmium in water, medicinal plants and soil samples. It could also be used successfully as an indicator electrode in the potentiometric titration of Cd2+ with EDTA (ethylenediaminetetraacetic acid).

New Polymeric Membrane Electrode for Clarithromycin Determination

New polymeric membrane electrodes has been developed for the determination of Clarithromycin. The electrodes were constructed by incorporating the Clarithromycintetraphenylborate ion pair complex into a polyvinylchloride matrix plasticized by four plasticizers, Di-octyl phthalate (DOP); Di-butyl phosphate (DBP); Acetophenone (AP); Di-butyl phthalate (DBPH). These electrodes give sub- Nernstian slopes (51.206, 53.930, 58.104 and 58.484 mV/decade) and linear ranges from (1×10 -5 -1×10 -3 , 1×10 -5 -1×10 -3 , 5×10 -5 -1×10 -3 and 1×10 -5 -1×10 -3 M) respectively. The best electrode was based on DBPH plasticizer which gave a slope 58.484 mV/decade, correlation coefficient 0.9961, detection limit of 9×10 -6 M, lifetime 20 day and displayed good stability and reproducibility and used to determine the Clarithromycin in pharmaceutical samples. The interferences measurements were studied using the separated method for selectivity coefficient determination. The pH and life time of the electrodes were also studied.

Biologically active Schiff bases as potentiometric sensor for the selective determination of Nd3+ ion

Novel multidentate Schiff bases 5-((1-(3-(3-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)-1H-indol-1-yl)propyl)-1H-indol-3-yl)methyleneamino)-1,3,4-thiadiazole-2-thiol (S1) and N-((1-(3-(3-((thiazol-2-ylimino)methyl)-1H-indol-1-yl)propyl)-1H-indol-3-yl)methylene)thiazol-2-amine (S2) were synthesized for the construction of Nd3+ ion-selective electrode. The polymeric membrane electrodes (PME) were fabricated along with various plasticizers and additive. It is found that the PME based on S1 having the composition (S1: (potassium tetrakis p-(chloro phenyl)borate) KTpClPB: (o-nitrophenyloctyl ether) o-NPOE: PVC≡4:2:58:36, w/w, mg) is found to be better. Thus, the coated graphite electrode (CGE) was constructed with the same composition and the results were compared with PME. The CGE is found to be better in comparison to PME with respect to all the potentiometric characteristics such as low detection limit (1.1×10−8molL−1), wide working concentration range (3.1×10−8–1.0×10−1molL−1), near Nernstian slope (19.8±0.3mVdecade−1 of activity), low response time (10s), shelf life time (105 days) and wide pH range (3.5–8.0). Both the PME and CGE were used for the quantifying the Nd3+ ion in various samples such as water, soil samples, binary mixtures and as an indicator electrode using EDTA. PME and CGE were also used for the determination of F− ion in mouth wash solution and tooth paste sample. Further the antibacterial activity of Schiff bases were examined by broth micro-dilution method and found that these are antibiotics against Staphylococcus aureus (Gram positive) and Escherichia coli (ATCC25922) (Gram negative).

Polymeric Membrane Neutral Phenol-Sensitive Electrodes for Potentiometric G-Quadruplex/Hemin DNAzyme-Based Biosensing

The first potentiometric transducer for G-quadruplex/hemin DNAzyme-based biosensing has been developed by using potential responses of electrically neutral oligomeric phenols on polymeric membrane electrodes. In the presence of G-quadruplex/hemin DNAzyme and H(2)O(2), monomeric phenols (e.g., phenol, methylphenols, and methoxyphenols) can be condensed into oligomeric phenols. Because both substrates and products are nonionic under optimal pH conditions, these reactions are traditionally not considered in designing potentiometric biosensing schemes. However, in this paper, the electrically neutral oligomeric phenols have been found to induce highly sensitive potential responses on quaternary ammonium salt-doped polymeric membrane electrodes owing to their high lipophilicities. In contrast, the potential responses to monomeric phenolic substrates are rather low. Thus, the G-quadruplex/hemin DNAzyme-catalyzed oxidative coupling of monomeric phenols can induce large potential signals, and the catalytic activities of DNAzymes can be probed. A comparison of potential responses induced by peroxidations of 13 monomeric phenols indicates that p-methoxyphenol is the most efficient substrate for potentiometric detection of G-quadruplex/hemin DNAzymes. Finally, two label-free and separation-free potentiometric DNA assay protocols based on the G-quadruplex/hemin DNAzyme have been developed with sensitivities higher than those of colorimetric and fluorometric methods. Coupled with other features such as reliable instrumentation, low cost, ease of miniaturization, and resistance to color and turbid interferences, the proposed polymeric membrane-based potentiometric sensor promises to be a competitive transducer for peroxidase-mimicking DNAzyme-involved biosensing.

Novel thiocyanate ion-selective electrodes based on a copper(II) complex of p-hydroxyacetophenone thiosemicarbazone as a carrier

A complex of copper(II) with p-hydroxyacetophenone thiosemicarbazone has been used to fabricate a polymeric membrane electrode (PME) and coated glassy carbon electrode (CGCE). The proposed electrodes showed excellent response characteristics to thiocyanate ions over a wide concentration range from 1.0 × 10−7 to 1.0 × 10−1 M for PME and 1.0 × 10−6 to 1.0 × 10−2 M for CGCE. Nernstian slopes exhibited were −59.7 ± 0.3 mV decade−1 for PME and −53.6 ± 0.4 mV decade−1 for CGCE with low detection limits of 4.3 × 10−8 and 4.1 × 10−7 M, respectively. The PME membrane electrode provides a more sensitive and stable device than the CGCE electrode. The PME has a wide functional pH range (2.5–10.5), fast response time (5 s), and could be used for approximately 4 months without any considerable divergence in the potential. The selectivity coefficient was determined by a matched potential method and fixed interference method. A good discriminating ability towards the SCN− ion compared to other anions has been observed. PME was successfully applied as an indicator electrode for potentiometric titration of thiocyanate ion with AgNO3. Further, the electrode was successfully applied to determine the thiocyanate content in physiological fluids (urine samples).

A polymeric membrane electrode for the detection of perchlorate in water at the sub-micro-molar level

A highly sensitive polymeric membrane electrode was synthesized for the detection of perchlorate in water. The membranes were characterized for thickness, potentiometric responses, and response time. Factors such as interfering anions, humic acid, and pH that may affect the performance of the electrode were investigated. The membrane electrode exhibited favorable selectivity toward perchlorate over interfering anions such as chloride, nitrate, sulfate, and bicarbonate in water and had a response time of ca. 5 s over the perchlorate concentration (activity) range of 10−6 to 10−1 M and a Nernstian slope of 58.5 ± 0.4 mV at room temperature. The potentiometric response of the electrode was pH independent in the range of 3.0 to 11.0 and had a perchlorate detection limit of 7.0 × 10−7 M (or 70 ppb). The polymeric membrane electrode was able to detect perchlorate ion at the sub-micro-molar level under conditions mimicking those of natural water systems.

Potentiometric Selectivity Of Polymer-Membrane Electrodes Based On Lanthanum With Tributyl phosphate (TBP) as Ionophore

Potentiometric Selectivity Of Polymer-Membrane Electrodes Based On Lanthanum With Tributyl phosphate (TBP) as Ionophore

Bending deformation characteristics of actuator with anion exchange polymer membrane and polyaniline electrode

To remove the metal electrode and comprise all-organic ionic polymer actuators, tri-layer actuators with anion exchange membranes and conducting polymer electrode were purposely fabricated by the simple attaching method with or without an adhesive layer. Three grades of Neosepta were used as the anion exchange membrane, and polyaniline (PANi) as the electrode. Despite the oxidation/reduction occurring, PANi functioned as the electrode for the actuators. The bending displacement of 7 mm was measured, which was comparable to that of the typical Nafion actuator. As the initial bending direction was the same as an actuator with a cation exchange membrane, the bending characteristics of the actuators and structural change in PANi during actuation were investigated. Open image in new window