Electrochemical properties of photocurable membranes for all-solid-state chemical sensors

The development of ion-selective electrodes with inner solid contact is described using photocurable acrylated polyurethane matrices and electron-ion exchanger (EI), which provides a reversible transition from electrical conductivity in the metal to ionic conductivity in the membrane phase. The application of a photocurable polymer matrix gives the possibility to use modern photolithographic techniques for the formation of all-solid-state chemical sensors. The influence of the polymer matrix and of the preparation of the membrane on the electro-chemical properties of calcium-selective membrane sensors is shown. For carbonate-selective membranes the possibility of improvement of electrochemical characteristics by incorporation of the anionic additive tetrakis (4-chlorophenyl) borate was studied. Received: 14 June 1997 / Revised: 23 September 1997 / Accepted: 9 October 1997     

Dissolvable membranes as sensing elements for microfluidics based biological/chemical sensors

We demonstrate a chemical and biological sensing mechanism in microfluidics that transduces chemical and biological signals to electrical signals with large intrinsic amplification without need for complex electronics. The sensing mechanism involves a dissolvable membrane separating a liquid sample chamber from an interdigitated electrode. Dissolution of the membrane (here, a disulfide cross-linked poly(acrylamide) hydrogel) in the presence of a specific target (here, a reducing agent-dithiothreitol) allows the target solution to flow into contact with the electrode. The liquid movement displaces the air dielectric with a liquid, leading to a change (open circuit to approximately 1 kOmega) in the resistance between the electrodes. Thus, a biochemical event is transduced into an electrical signal via fluid movement. The concentration of the target is estimated by monitoring the difference in dissolution times of two juxtaposed sensing membranes having different dissolution characteristics. No dc power is consumed by the sensor until detection of the target. A range of targets could be sensed by defining membranes specific to the target. This sensing mechanism might find applications in sensing targets such as toxins, which exhibit enzymatic activity.     

Electrochemical sensors for real-world applications

Journal of Solid State Electrochemistry -     

Enzyme-entrapping membranes for enzyme sensors

A reliable method of physically immobilizing enzymes in cellulose triacetate (TAC) membranes was developed. The method has several advantages compared with analogous ones currently employed; it was possible to prepare enzyme sensors based on immobilized glucose oxidase (GOD) for determination of glucose in standard solutions and control sera, and based on GOD and invertase for determination of sucrose.     

Electrochemical plasmonic sensors

The enormous progress of nanotechnology during the last decade has made it possible to fabricate a great variety of nanostructures. On the nanoscale, metals exhibit special electrical and optical properties, which can be utilized for novel applications. In particular, plasmonic sensors including both the established technique of surface plasmon resonance and more recent nanoplasmonic sensors, have recently attracted much attention. However, some of the simplest and most successful sensors, such as the glucose biosensor, are based on electrical readout. In this review we describe the implementation of electrochemistry with plasmonic nanostructures for combined electrical and optical signal transduction. We highlight results from different types of metallic nanostructures such as nanoparticles, nanowires, nanoholes or simply films of nanoscale thickness. We briefly give an overview of their optical properties and discuss implementation of electrochemical methods. In particular, we review studies on how electrochemical potentials influence the plasmon resonances in different nanostructures, as this type of fundamental understanding is necessary for successful combination of the methods. Although several combined platforms exist, many are not yet in use as sensors partly because of the complicated effects from electrochemical potentials on plasmon resonances. Yet, there are clearly promising aspects of these sensor combinations and we conclude this review by discussing the advantages of synchronized electrical and optical readout, illustrating the versatility of these technologies.     

Element profiles in galvanostatically polarized K+-selective all-solid-state sensors with poly(vinyl chloride)-based membranes

The influence of galvanostatic polarization on ion concentration profiles in all-solid-state ion-selective sensors was studied. As a model system K⁺-selective electrode with poly(vinyl chloride)-based membrane, ionophore–valinomycin and polypyrrole doped by chloride ions as ion-to-electron transducer was selected. The ion exchanger—a typical component of ion-selective membrane—was replaced by lipophilic salt: tetradodecylammonium tetrakis(4-chlorophenyl) borate to avoid spontaneous extraction of potassium ions. Potassium, sodium, and chlorine distribution within the sensor phases were studied using laser ablation micro-sampling followed by inductively coupled plasma mass spectrometry measurements. The experiments revealed accumulation of potassium ions in course of cathodic galvanostatic polarization, with concentration decreasing by moving inside the ion-selective membrane. The surface content of K⁺ ions was found to be linearly dependent on applied current. Influence of sequential anodic galvanostatic polarization or open circuit conditioning applied after cathodic polarization revealed only limited recovery of the initial concentration profiles in the membrane.     

Development of photocurable compositions with special properties

New photopolymerizable compositions (PPC) based on radically curable acrylic monomers and oligomers and cationically curable epoxy oligomers are developed. The properties of these compositions are studied, and the possibility of their application in technology of 3D-prototyping and coating of fiberglass plastics is shown.     

Electrochemical sensors for monitoring environmental pollutants

Stricter environmental controls on the emission and discharge of chemical pollutants are creating an increased demand for the development of improved chemical sensor devices. Although electrochemical sensors show great promise for this task, their utility has been constrained by a number of practical problems, the most serious being the effect of surface adsorption of impurities leading to non-reproducible response. This review presents a survey of recent advances in electrochemical sensor technology which have attempted to improve the performance of these devices. Three main areas of development have been addressed; advances in sensor design and measurement techniques, novel approaches to conferring electrode selectivity and the use of microminiaturization and microelectronics fabrication techniques. Recent applications and future prospects for the measurement of toxic metals, organics and gases including volatile organic compounds are surveyed.     

Electrochemical sensors for oxidative stress monitoring

Electrochemical sensors are ideally suited for the detection of reactive oxygen and nitrogen species (ROS and RNS) generated during biological processes. This review discusses the latest work in the development of electrochemical microsensors for ROS/RNS and their applications for monitoring oxidative stress in biological systems. The performance of recent designs of microelectrodes and electrode materials is discussed along with their functionality in preclinical models of drug efficacy, mitochondrial distress, and endothelial dysfunction. Challenges and opportunities in translating this methodology to study the pathophysiology associated with various diseases are discussed.     

Electrochemical sensors for environmental gas analysis

The application of electrochemical sensors for measurement of concentration of pollutant gases in air in the part-per-billion (10⁹) range is reviewed. Performance-limiting factors, particularly the effects of extremes and of relatively rapid changes in ambient temperature and humidity, are noted. Variations in composition of the electrolyte in the meniscus at the electrode–gas interface and instability of the solid–liquid–gas contact line, causing important variations in current due to background electrode reactions, are deduced and suggested as the reason for the performance limitations. Suggestions are made for mitigation through instrument design.     

Electrochemical properties of all-solid-state lithium batteries with amorphous titanium sulfide electrodes prepared by mechanical milling

Amorphous titanium trisulfide (TiS₃) active materials were prepared by ball milling of an equimolar mixture of crystalline titanium disulfide (TiS₂) and sulfur. A high-resolution transmission electron microscope image revealed no periodic lattice fringes on the amorphous TiS₃. The all-solid-state lithium secondary batteries using a sulfide solid electrolyte and the amorphous TiS₃ electrode showed high capacity of greater than 300 mAh g^?1 for 10 cycles. The amorphous TiS₃ had a higher capacity than the mixture of crystalline TiS₂ and S, which was used as the starting material of amorphous TiS₃. The X-ray diffraction patterns and the Raman spectra of the amorphous TiS₃ electrode after the first and tenth charge–discharge measurements were similar to those before the measurement. The amorphous structure of TiS₃ did not change greatly during the first few cycles. The all-solid-state cells with the amorphous TiS₃ electrode showed higher initial coulombic efficiency because the amorphous TiS₃ active material retained its structure during the initial electrochemical test.     

Rapid bioanalysis with chemical sensors: novel strategies for devices and artificial recognition membranes

The increasing importance of biological analytes in chemistry has triggered the development of a vast number of techniques for rapidly assessing them. Aside from microbiological test methods, a wide range of analytical sensor and detection methods are being developed. Within this article, we review the literature on this topic from the last five years, stressing two main aspects of method development. The first aspect is the design of novel analytical strategies and transducers to generate signals more sensitively, more rapidly and more efficiently. Most of the progress in this field has focused on electrochemical detection, although novel approaches to optical and mass-sensitive measurements have been reported. Second, we provide an overview of two main approaches to creating artificial interaction layers for sensors based on tailored interaction sites in polymeric or biomimetic systems. The most prominent of these approaches is (molecular) imprinting, where selectivity is achieved by directly templating a polymer material with the target analyte or a model compound, thus achieving biomimetic interaction sites within both thin films and particles.     

Electrochemical properties of hydrophilic weak-acid membranes from hydrolysed polyacrylonitrile—I. Effect of cross-linking and chemical composition

Gels cross-linked to various degrees and containing various amounts of nitrile, amide and carboxylic groups were prepared by polymerizing acrylonitrile at various concentrations in aqueous 70 per cent ZnCl₂ solution and by hydrolysis of polymers for various times in HCl vapours. Chemical characteristics of gels, concentration membrane potentials, membrane functions and permselectivities in KCl solutions were determined. It was proved that under the conditions used (pH close to 7, content of acrylic acid in the copolymer only 1·4–3·9 mole %). cross-linking is the decisive factor for permselectivity and ideality of the membrane functions. Cross-linking yielded almost 100 per cent permselectivity values and a slope of the membrane function of about 55 mV/decade. Further hydrolysis impairs the ideality of membranes, since the increase in swelling outweighs the effect of the increase in concentration of the active groups. Variability of the density of the ionizable groups is not sufficient to explain differences in the behaviour of the membranes under investigation.     

Electrochemical non-enzymatic glucose sensors

The electrochemical determination of glucose concentration without using enzyme is one of the dreams that many researchers have been trying to make come true. As new materials have been reported and more knowledge on detailed mechanism of glucose oxidation has been unveiled, the non-enzymatic glucose sensor keeps coming closer to practical applications. Recent reports strongly imply that this progress will be accelerated in ‘nanoera’. This article reviews the history of unraveling the mechanism of direct electrochemical oxidation of glucose and making attempts to develop successful electrochemical glucose sensors. The electrochemical oxidation of glucose molecules involves complex processes of adsorption, electron transfer, and subsequent chemical rearrangement, which are combined with the surface reactions on the metal surfaces. The information about the direct oxidation of glucose on solid-state surfaces as well as new electrode materials will lead us to possible breakthroughs in designing the enzymeless glucose sensing devices that realize innovative and powerful detection. An example of those is to introduce nanoporous platinum as an electrode, on which glucose is oxidized electrochemically with remarkable sensitivity and selectivity. Better model of such glucose sensors is sought by summarizing and revisiting the previous reports on the electrochemistry of glucose itself and new electrode materials.     

Electrochemical sensors for sulfur- and lead-containing gases

The possibility of using solid-electrolyte transducers with nonstoichiometric electrodes was studied, and the effect of the material and nonstoichiometry of lead monochalkogenides as measurement electrodes on the work of transducers was considered. The reliability of the results obtained was substantiated by comparing the calculated thermodynamic properties of the measurement electrodes with the corresponding reference values. The effect of nonstoichiometry was assessed from coulometric titration curves. It was noticed that the defect type affects the sensitivity of the transducer. The effect of the surface of the measurement electrode on the process of gas analysis was assessed. The applicability region for the transducers under study was indicated.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 2, 2005, pp. 193–197.Original Russian Text Copyright © 2005 by Leushina, Makhanova.Presented at the International Forum Analytics and Analysts, Voronezh, 2003.This revised version was published online in April 2005 with corrections to the author names and book review format.     

Lipophilic and immobilized anionic additives in solvent polymeric membranes of cation-selective chemical sensors

Lipophilic borate salts are frequently used as anionic additives in potentiometric and optical cation-selective sensors based on solvent polymeric membranes. The lifetime of such membranes may be limited owing to chemical decomposition and leaching of the components. Borate salts, in particular, are decomposed in the presence of acids in the membrane. Adequately substituted borate salts and sulphonic acids, such as sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, sodium tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate and dinonylnaphthalenesulphonic acid (DNSS), are shown to be sufficiently stable as membrane additives. Furthermore, lipoholic mobile or immoblizied sulphonic acids [DNNS or poly(2-acrylamido-2-methyl-1-propanesulphonic acid-co-styrene), respectively were also tested as anionic additives. Their influence on the selectivity behaviour of the sensor is attributed to their strong association with positively charged species in the membrane phase. It may be kept small by choosing ionophores that from stable complexes with the analyte.     

硫醇－磷脂混合双层膜的电化学性质及其与蜂毒素的相互 作用研究

报道了硫醇－磷脂混合双层膜的循环伏安和电化学交流阻抗行为研究,并用电化学方法考察了蜂毒素与其相互作用,实验中通过冷冻表面沾有磷脂溶液的硫醇单层膜制备混合双层膜,研究表明双层膜在电极表面形成致密的绝缘层,阻碍了电极表面的电子传递,在双层膜体系上引入的蜂毒素可在膜表面上形成孔洞,破坏膜的绝缘性,降低膜电阻,增加膜电容,使带负电的探针Fe(CN)6^3-的氧化还原反应速度加快。     

Electrochemical properties and structure of ion-exchange membranes upon thermochemical treatment

The effect of temperature-induced morphological changes on the electrochemical and physicochemical properties of the heterogeneous sulfo cation-exchange membrane MK-40 in aqueous, alkaline, and acidic media is subjected to comparative analysis. The deviation between the surface and volume microstructure of swollen membrane samples after their chemical conditioning and thermochemical treatment are visualized by a scanning electron microscope. The porosity and the fraction of the ion-exchange component in membranes subjected to heating in water and aggressive media are observed to increase more noticeably in their surface layer as compared with their volume. The maximum effect thus modified structural characteristics on the transport (conductivity, diffusion permeability, selectivity) and physicochemical (exchange capacity, water content, density, linear sizes) properties is observed for MK-40 membrane samples when heated in a sulfuric acid solution. The effect of thermal destruction of inert polymers (divinylbenzene, caprone) involved in the membrane composition on the transport characteristics is revealed.     

Electrochemical properties and spectrophotometry of membranes based on holmium tetraphenylporphyrinchloride

Protolytic properties of holmium tetraphenylporphyrinchloride were studied by the method of two-phase spectrophotometric titration with potentiometric monitoring of pH of the medium. Apparent constants of the heterophase reaction of the exchange of an anion for the hydroxide ion were determined. It was found that the membranes based on holmium tetraphenylporphyrinchloride with dibutyl phthalate as a solvent-softener are selective to ions of alkaline earth metals (Ca²⁺ and Ba²⁺) in the region of pH > 7 over the concentration range from 1 up to 1×10⁻⁴ M. Selectivity coefficients were determined by two independent methods: the method of biion potentials and the method of mixed solutions. The found selectivity series coincides with traditional Hofmeister series for cations.