Potentiometric response of graphite electrodes coated with modified polymer films

Graphite electrodes coated with chemically-modified polymer films are described. Several different polymers were used, including poly(acrylic acid), poly[triethyl(vinylbenzyl)ammonium chloride], poly[trihexyl(vinylbenzyl)ammonium chloride], and poly[trihexyl(vinylbenzyl)ammonium thiocyanate]. A cation-responsive electrode can be prepared from poly(acrylic acid)-coated graphite. Anion-responsive electrodes can be prepared from graphite coated with polymeric quaternary amines. In these electrodes, the ion-sensing species is irreversibly attached to the polymer (rather than physically entrapped within a polymer matrix); this factor eliminates leaching of the active component, and the addition of a plasticizer is unnecessary. A selective sensor for thiocyanate is described; it yields a Nernstian response over the concentration range 1 × 10^?1–1 × 10^?5 M sodium thiocyanate.     

The interaction of lipid modified pseudopeptides with lipid membranes

We have studied the structure of two lipopeptides based on the simple dipeptide building block L-Phe-D-Oxd. These peptides have been reported previously to form fiber-like materials. The lipopeptides synthesized here had the structures C(n)(2)H((2n+1))CO-L-Phe-D-Oxd-OBn or C(n)(2)H((2n+1))CO-D-Phe-L-Oxd-OBn with n = 5 or 11. Addition of the N-terminal lipid modification did not cause a major disturbance of the structures these molecules form. The lipid modifications themselves showed highly rigid structures as inferred from solid-state (2)H NMR. The peptide backbone showed (13)C NMR chemical shifts in agreement with β-sheet secondary structure. Addition of a lipid modification to the N-terminus is a common motif in biology to attach proteins to the membrane. Therefore, we also investigated the lipopeptides in the presence of synthetic POPC bilayers. Two different molecular species were detected under these circumstances: (i) lipopeptide monomers that showed chain order parameters similar to those of the host membrane, (ii) lipopeptide aggregates that exhibited very similar structures and dynamics as the crystalline aggregates. Overall, the lipopeptides showed a well defined and rigid secondary structure that is in agreement with fibrillar aggregates previously detected for those peptides without the lipid modification.     

Potentiometric pH sensors based on chemically modified electrodes with electropolymerized metal-tetraaminophthalocyanine

Potentiometric pH sensors based on polymer film were prepared by electropolymerization of the monomer nickel(II)-4,4',4',4'-tetraaminophthalocyanine (NiTAPc) or copper(II)-4,4',4',4'-tetraaminophthalocyanine (CuTAPc) on glassy carbon (GC) electrodes. The polymer of metal tetraaminophthalocyanine (p-MTAPc) film coated electrodes show a slope of 55 +/- 1 mV/pH (at 20 degrees C) and nearly Nernstain potentiometric response to pH over the range of pH 1-13. The electrodes possess good potential reproducibility and high selectivity, and are useful sensing devices in pH determination and end-point indication of acid-base potentiometric titration.     

一次性铵离子ISFET的研究

本文报道一种基于四苯硼钠的离子敏感场效应晶体管(ISFET)。并对器件性能的影响因素进行详尽讨论,确立了以邻苯二甲酸二丁酯(DBP)为增型塑剂,器件的性能最佳。ISFET的线性范围为1.0～7.5×10-5mol/L,检出限为6.0×10-5mol/L,斜率为58mV/decade,适宜的pH范围为4.2～8.4。     

Potentiometric microdetermination of aluminium in organic compounds after combustion in a modified oxygen flask

The microdetermination of aluminium in organic compounds by oxygen flask combustion, a simultaneous fusioncombustion procedure was developed, in which the sample in a mixture with KHSO₄ is burnt in a modified oxygen flask under suitable conditions so that the alumina formed is immediately converted into the corresponding water-soluble sulfate. 2.4 ml of 6M HCl are used as absorption solution, in which the combustion residue is completely dissolved by boiling. The solution is then transferred to a titration cell, neutralized with NaOH in the presence of methyl red, and the Al(III) is finally determined in a buffered 40% (V/V) dioxane solution by potentiometric titration with 0.1 M NaF. The results obtained were accurate within ±0.13%; the recoveries of Al are in the range of 99.00 to 99.90%; the standard deviation amounts to 0.06%. The potentiometric titration of Al(III) with fluoride as well as the conditions of the oxygen flask combustion of organic aluminium compounds are discussed.     

Potentiometric determination of lysine in aqueous solutions using MF-4SK modified perfluorinated membranes

A selective potentiometric sensor was developed on the basis of MF-4SK modified perfluorinated sulfonic cation-exchange membranes for determining lysine monohydrochloride in mixed aqueous solutions of neutral amino acids. It was shown that the treatment of MF-4SK membranes in ethylene glycol increased the sensitivity of the sensor. The use of MF-4SK perfluorinated sulfonic cation-exchange membranes for determining lysine in aqueous solutions is based on a protolytic reaction; as a result of this reaction, single-charged lysine ions from solution are transferred into doubly charged ions in the membrane phase. The Donnan potential at an individual boundary between the studied solution and the membrane is the sensor response. The response time was 10–15 min. The concentration constants of the sensor selectivity to lysine in the presence of glycine, alanine, and leucine did not exceed 0.019. The relative error of determining lysine monohydrochloride in the studied solutions of neutral amino acids was 2–5%.     

Potentiometric response and mechanism of anionic recognition of heterocalixarene-based ion selective electrodes

The ion selective electrode (ISE)-based potentiometric approach is shown to be an effective means of characterizing the anion recognition sites in the molecular receptor calix[2]pyridino[2]pyrrole (CPP). In particular, potentiometric pH-measurements involving the use of experimental PVC-membranes based on CPP revealed the existence of both mono- and diprotonated forms of the receptor under readily accessible conditions. Based on these analyses, apparent surface protonation constants for this heterocalixarene were found to lie between 8.5-8.9 (pK_B1) and 3.3-3.8 (pK_B2). CPP was found to interact with targeted anionic analytes based on both coulombic and hydrogen bond interactions, as inferred from varying the kinds of ionic sites present within the membrane phase. Potentiometric selectivity studies revealed that CPP preferred “Y-shaped” anions (e.g. acetate, lactate, benzoate) over spherical anions (e.g. fluoride and chloride), fluoride over chloride within the set of spherical anions, and the ortho-isomer over the corresponding meta- and para-isomers in the case of hydroxybenzoate (salicylate and congeners). In the context of this study, the advantages of potentiometric determinations of acetylsalicylic acid using optimized PVC-membranes based on CPP relative to more conventional PVC-membrane ISEs based on traditional anion exchanger were also demonstrated.     

Potentiometric applications of the response of a sodium-selective glass electrode to silver

The use of a sodium-sensitive glass electrode for the determination of silver ion is demonstrated.     

Potentiometric

Ohne Zusammenfassung     

ISFET immunosensor improvement using amine-modified polystyrene nanobeads

Antigen-based sensing is recognized as a rapid and sensitive analysis among bioresearch groups. The potential of “on-site” analysis in such devices has been accompanied by some problems. Fabrication of silicon compatible and highly sensitive biosensors has been the center of excessive research within the past few years. In this paper, we report fabrication of two types of sensitive liquid oxide semiconductor (LOS) biosensors using nanostructures. These devices have been manufactured and characterized as immunosensors. These two types of sensors have been produced using different platforms for immobilization of proteins; one based on a functionalized silicon dioxide surface by 3-aminopropyltriethoxysilane (APTES) and another on the basis of using 50-nm amine-modified polystyrene nanobeads. The polystyrene platform not only benefits from its nanosize and high surface to volume ratio but also does not need any new protocol than what is already used for traditional immunosensing system. These sensors measure the change of threshold voltage of the semiconductor inversion inside the capacitor due to the bonding of antibodies to the linked peptides on the surface. Measurements showed that the sensitivity of 50-nm polystyrene-based sensor is much more than the oxide-based one. The nanobeads were then chosen to cover the gate of the ISFET for the amplified sensing. The ISFET devices were biased in a subthreshold region to demonstrate the maximum sensitivity to the accumulated charge on the gate. Repeatable results after different stress tests were obtained, which proves the suitability and reliability of the polystyrene nanobead platform for this application. Finally, a calibration curve has been derived that can be used for real sample measurements. The detection limit of 1.0152 μg/ml was calculated for the fabricated sensor.

Open image in new window

Graphical abstract

     

硅钨酸-丁氯喘ISFET的研制与应用

以硅钨酸为活性物质 ,邻苯二甲酸二辛酯为增塑剂制成的 5%聚氯乙烯四氢呋喃溶液 ,涂在离子敏感场效应晶体管 ( ISFET)的栅极上 ,形成对药物敏感的场效应晶体管 ( Drug FET)。由该 Drug FET制成的化学传感器对盐酸丁氯喘的线性响应范围为 1 .0 0× 1 0 - 5～ 1 .50× 1 0 - 1mo L/L,斜率为 60 m V/Δpc,适宜的 p H范围为 4.5～8.2 ,检测下限为 8.50× 1 0 - 6 mo L/L。用该传感器分析了丁氯喘片剂的含量 ,和分光光度法测定的结果相一致     

Proteomics annotation of lipid rafts modified by virus infection

Lipid rafts are sphingolipid- and cholesterol-enriched membrane microdomains, which are involved in entry, assembly and budding of various types of viruses. Identification of rafts associated proteins modified by virus infection could therefore provide novel insights into the mechanisms of virus infection as well as the development of new biomarkers for diagnosis and drug development. Proteomic approaches, such as LC-ESI-MS/MS, two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), two-dimensional difference gel electrophoresis (2D-DIGE), isotope-coded affinity tags (ICAT), Proteolytic 1?O Labeling, isotope Tags for Relative and Absolute Quantification (iTRAQ), Stable Isotope Labeling with Amino acids in Cell culture (SILAC) and Multidimensional Protein Identification Technology (MudPIT), provide the large scale and unbiased platform to determine the dynamic profiles of the lipid rafts proteome. In this review, we summarized the research advance regarding modern proteomics analysis of host lipid rafts alterations in response to diverse virus infection.     

Characteristics of reference electrodes using a polymer gate ISFET

A new type of ISFET with a Parylene gate as a site-free and ion-blocked membrane has been proposed for a reference electrode. The reference ISFET should be insensitive to the variation of ion concentrations of all ions or a specific ion in the electrolyte and should have a constant gate surface potential. In this paper, the operation of this reference ISFET is analysed by the site binding model and the conditions required to make the gate surface potential constant are examined. In general, the surface potential of an electrolyte-insulator-semiconductor (EIS) system is determined by two factors, i.e., the available surface site density of the insulator and the total charge density of the semiconductor, and it can be made constant by controlling the total charge density of the semiconductor. The preliminary experimental results on the electrolyte-Parylene-Si diode and ISFET are in good agreement with the theoretical calculations and suggest that a reference ISFET could be realized by using the Parylene gate.     

Potentiometric pH response of membranes prepared with various aminated-poly (vinyl chloride) products

The preparation and potentiometric pH response properties of membranes formulated with various aminated-poly(vinyl chloride) (PVC-NH₂) products are described. Products containing secondary and/or primary amino functional groups are obtained by modifying PVC with mono- and/or diamines, respectively. Blank membranes prepared with either type of aminated-polymer exhibit nearly Nernstian potentiometric pH responses over different pH ranges. In general, membranes based on diamino products exhibit pH response over a wider range (5–10.5) than membranes formulated with monoamino products (<8.0). These potentiometric results are used to estimate the basicity of the various primary and secondary amino sites in the membrane phases.Dedicated to Professer W. Simon on the occasion of his 60th birthday     

Photocurable ISFET for anionic surfactants. Monitoring of photodegradation processes

The preparation of a new ion-selective field-effect transistor (ISFET) based on a photocurable membrane sensitive to anionic surfactants is described. The membrane is formed by an urethane-acrylate matrix with 2-cyanophenyl octyl ether as the plasticiser. When compared to conventional ion-selective electrodes, the prepared ISFETs do not show significant differences in sensitivity and reproducibility (P=0.05). When calibrating with dodecylbenzenesulfonate (DBS(-)) the prepared ISFETs show a nernstian behaviour, with a slope of 57.5 mV per decade. The linear working range is 1.0x10(-3) to 3.0x10(-6) M DBS(-) and the detection limit is 1.2x10(-6) M. The response times were below 0.7 min in all cases (95% of the step change). As the application, photodegradation processes using titanium dioxide dispersions, were monitored for two common anionic surfactants: DBS(-), being aromatic, and the more alkylic dodecylsulfate, DS(-). The determination of surfactant concentration was performed following a standard addition methodology, using ISFETs as the sensors, and without any previous separation stages. The degradation kinetics in both cases are first-order processes, with half-life times (t(0.5)) of 31.5 min for DBS(-) and 52.0 min for DS(-).     

Assembly of lipid bilayers on silica and modified silica colloids by reconstitution of dried lipid films

A method is presented for the assembly of lipid bilayers on silica colloids via reconstitution of dried lipid films solvent-cast from chloroform within packed beds of colloids ranging from 100 nm to 10 μm in diameter. Rapid solvent evaporation from the packed bed void volume results in uniform distribution of dried lipid throughout the colloidal bed. Fluorescence measurements indicate that significant, if not quantitative, retention of DOPC or DPPC films cast between sub-bilayer and multilayer quantities occurs when the colloids are redispersed in aqueous solution. Phospholipid bilayers assembled in this manner are shown to effectively passivate the surface of 250 nm colloids to nonspecific adsorption of bovine serum albumin. The method is shown to be capable of preparing supported bilayers on colloid surfaces that do not generally support vesicle fusion such as poly(ethylene glycol) (PEG) modified silica colloids. Bilayers of lipids that have not been reported to self-assemble by vesicle fusion, including gel-phase lipids and single-chain diacetylene amphiphiles, can also be formed by this method. The utility of the solid-core support is demonstrated by the facile assembly of supported lipid bilayers within fused silica capillaries to generate materials that are potentially suitable for the analysis of membrane interactions in a microchannel format.