Polymers in sensor applications

Åbo Akademi University, Process Chemistry Centre, c/o Laboratory of Analytical Chemistry, Biskopsgatan 8, FI-20500 Turku-Åbo, Finland; Faculty of Material Science and Ceramics, AGH-University of Science and Technology, Al. Mickiewicza 30, PL-30059 Cracow, Poland; and Åbo Akademi University, Process Chemistry Centre, c/o Center for Process Analytical Chemistry and Sensor Technology (ProSens), Biskopsgatan 8, FI-20500 Turku-Åbo, Finland

Potentiometric Ion Sensors

The study of electrochemical behavior of bioactive molecules has become one of the most rapidly developing scientific fields. Biotechnology and biomedical engineering fields have a vested interest in constructing more precise and accurate voltammetric/amperometric biosensors. One rapidly growing area of biosensor design involves incorporation of carbon-based nanomaterials in working electrodes, such as one-dimensional carbon nanotubes, two-dimensional graphene, and graphene oxide. In this review article, we give a brief overview describing the voltammetric techniques and how these techniques are applied in biosensing, as well as the details surrounding important biosensing concepts of sensitivity and limits of detection. Building on these important concepts, we show how the sensitivity and limit of detection can be tuned by including carbon-based nanomaterials in the fabrication of biosensors. The sensing of biomolecules including glucose, dopamine, proteins, enzymes, uric acid, DNA, RNA, and H2O2 traditionally employs enzymes in detection; however, these enzymes denature easily, and as such, enzymeless methods are highly desired. Here we draw an important distinction between enzymeless and enzyme-containing carbon-nanomaterial-based biosensors. The review ends with an outlook of future concepts that can be employed in biosensor fabrication, as well as limitations of already proposed materials and how such sensing can be enhanced. As such, this review can act as a roadmap to guide researchers toward concepts that can be employed in the design of next generation biosensors, while also highlighting the current advancements in the field.

http://pubs.acs.org/doi/pdf/10.1021/acsnano.5b05690

Engineered Carbon-Nanomaterial-Based Electrochemical Sensors for Biomolecules

Conducting polymers, i.e., electroactive conjugated polymers, are useful both as ion-to-electron transducers and as sensing membranes in solid-state ion-selective electrodes. Recent achievements over the last few years have resulted in significant improvements of the analytical performance of solid-contact ion-selective electrodes (solid-contact ISEs) based on conducting polymers as ion-to-electron transducer combined with polymeric ion-selective membranes. A significant amount of research has also been devoted to solid-state ISEs based on conducting polymers as the sensing membrane. This review gives a brief summary of the progress in the area in recent years.

Conducting Polymer‐Based Solid‐State Ion‐Selective Electrodes

In the thematic review dedicated to polyoxometalate (POM) chemistry published in Chemical Reviews in 1998, no contribution was devoted to theory This is not surprising because computational modelling of molecular metal-oxide clusters was in its infancy at that time Nowadays, the situation has completely changed and modern computational methods have been successfully applied to study the structure, electronic properties, spectroscopy and reactivity of POM clusters Indeed, the progress achieved during the past decade has been spectacular and herein we critically review the most important papers to provide the reader with an almost complete perspective of the field

Structure, properties and reactivity of polyoxometalates: a theoretical perspective

Segmented sandwich membrane method of studying stoichiometry and stability constants of ion−ionophore complexes in ion-selective membranes is considered in detail. The experimental data (reported earlier in Russian) concerning complexes of various ions with valinomycin, with H+-selective neutral ionophore hexabutyltriamidophosphate, and with anion-binding neutral ionophore p-hexyl trifluoroacetylbenzoate is presented in a compact form. Advantages of titration technique in the sandwich membrane method (the presence of an internal criterion of reliability, and the possibility of direct determination of complex stoichiometry coefficients) are specially addressed. Biases of the estimates of the constants caused by ion-pair formation in real membranes and by diffusion potential are analyzed by means of computer simulations. The possibility of revealing two coexisting complexes with different compositions is also discussed.

Potentiometric Estimation of the Stability Constants of Ion−Ionophore Complexes in Ion-Selective Membranes by the Sandwich Membrane Method: Theory, Advantages, and Limitations

The advantages and disadvantages of the PVC matrix of ion-selective electrodes are briefly discussed. Some of newly designed ion-selective electrodes (ISEs) with PVC membranes are mentioned. Emphasis is laid on what seems to be known about PVC membranes and on some of the problems which remain unsolved, as yet. The selectivity patterns of neutral carrier-based membranes and the so-called anion interference with the cationic response of the membranes are discussed in the frame of a thermodynamical approach. It is shown that this approach, especially taking into account the possibility for any ion to present in a membrane a number of different species (‘multi-species approach’) allows to describe in detail the selectivity as well as the anion interference. Among the problems which remain unsolved, three questions are discussed: (i) whether the diffusion potential contributes significantly to the membrane potential; (ii) what is the origin of the cation permselectivity of neutral carrier-based membranes, and (iii) what is the role of the PVC in membranes beside its mechanical role.

Ion-selective electrodes in PVC matrix

The recent advances in the theory and practice of potentiometric, conductometric and optical sensors based on ionophores are critically reviewed. The role of the heterogeneity of the sensor/sample systems is emphasized, and it is shown that due to this heterogeneity such sensors respond to the analyte activities rather than to concentrations. The basics of the origin of the response of all three kinds of ionophore-based sensors are briefly described. The use of novel sensor materials, new preparation and application techniques of the sensors as well as advances in theoretical treatment of the sensor response are analyzed using literature sources published mainly from 2012 to 2014. The basic achievements made in the past are also addressed when necessary for better understanding of the trends in the field of ionophore-based sensors. The bibliography includes 295 references.

http://iopscience.iop.org/article/10.1070/RCR4506/pdf

Advances and trends in ionophore-based chemical sensors

An overview is presented on the materials for the membranes of the ionophore-based ion-selective electrodes (ISEs). The basics of these membranes are briefly discussed. Bearing in mind that polyvinylchloride (PVC) is so far predominating as the ionophore-based ISE membrane matrix, and the limited life-time of these electrodes is due to an insufficient lipophilicity of the membrane components, the plasticizers in the first place, a discussion is presented on polymers alternative to PVC and ionophores immobilized on the polymer backbone. Data are presented on ISEs with membranes based on perfluorocompounds, which are especially important for the medical and biological applications. Studies are briefly described where instead of the replacement of PVC with self-plasticized polymers, the low-molecular plasticizers are replaced with polymeric analogs, retaining PVC as the polymeric matrix. Use of ionic liquids as the ISE membrane components is discussed, together with the interpretation of the literature data on the regularities in the functioning of such electrodes. Issues, studied mostly from the material science view are discussed throughout the review in their relation to electrochemistry.

Materials for the ionophore-based membranes for ion-selective electrodes: Problems and achievements (review paper)

Linear Nernstian response is obtained for a neutral ionophore-based Ca2+-selective electrode down to 10−10 M CaCl2 by means of galvanostatic polarization. The densities of the applied cathodic curr...

Konstantin N. Mikhelson

Papers

Potentiometric Estimation of the Stability Constants of Ion−Ionophore Complexes in Ion-Selective Membranes by the Sandwich Membrane Method: Theory, Advantages, and Limitations

Ion-selective electrodes in PVC matrix

Advances and trends in ionophore-based chemical sensors

Materials for the ionophore-based membranes for ion-selective electrodes: Problems and achievements (review paper)

Obtaining Nernstian Response of a Ca2+-Selective Electrode in a Broad Concentration Range by Tuned Galvanostatic Polarization