Preparation and properties of some ion selective membranes: A review

Recent advances in nanomaterial-based solid-contact ion-selective electrodes

Solid-contact ion-selective electrodes (SC-ISEs) are advanced potentiometric sensors with great capability to detect a wide range of ions for the monitoring of industrial processes and environmental pollutants, as well as the determination of electrolytes for clinical analysis. Over the past decades, the innovative design of ion-selective electrodes (ISEs), specifically SC-ISEs, to improve potential stability and miniaturization for in situ/real-time analysis, has attracted considerable interest. Recently, the utilisation of nanomaterials was particularly prominent in SC-ISEs due to their excellent physical and chemical properties. In this article, we review the recent applications of various types of nanostructured materials that are composed of carbon, metals and polymers for the development of SC-ISEs. The challenges and opportunities in this field, along with the prospects for future applications of nanomaterials in SC-ISEs are also discussed.

Integrating microneedles and sensing strategies for diagnostic and monitoring applications: The state of the art

Microneedles (MNs) offer minimally-invasive access to interstitial fluid (ISF) - a potent alternative to blood in terms of monitoring physiological analytes. This property is particularly advantageous for the painless detection and monitoring of drugs and biomolecules. However, the complexity of the skin environment, coupled with the inherent nature of the analytes being detected and the inherent physical properties of MNs, pose challenges when conducting physiological monitoring using this fluid. In this review, we discuss different sensing mechanisms and highlight advancements in monitoring different targets, with a particular focus on drug monitoring. We further list the current challenges facing the field and conclude by discussing aspects of MN design which serve to enhance their performance when monitoring different classes of analytes.

An ion-selective chemiresistive platform as demonstrated for the detection of nitrogen species in water

The use of ion-selective electrodes (ISE) is a well-established technique for the detection of ions in aqueous solutions but requires the use of a reference electrode. Here, we introduce a platform of ion-selective chemiresistors for the detection of nitrogen species in water as an alternative method without the need for reference electrodes. Chemiresistors have a sensitive surface that is prone to damage during operation in aqueous solutions. By applying a layer of ion-selective membrane to the surface of the chemiresistive device, the surface becomes protected and highly selective. We demonstrate both anion-selective (NO3-, NO2-) and cation-selective (NH4+) membranes. The nitrate sensors are able to measure nitrate ions in a range of 2.2-220 ppm with a detection limit of 0.3 ppm. The nitrite sensors respond between 67 ppb and 67 ppm of nitrite ions (64 ppb detection limit). The ammonium sensors can measure ammonium concentrations in a wide range from 10 ppb to 100 ppm (0.5 ppb detection limit). The fast responses to nitrate and nitrite are due to a mechanism involving electrostatic gating repulsion between negative charge carriers of the film and anions while ammonium detection arises from two mechanisms based on electrostatic gating repulsion and adsorption of ammonium ions at the surface of the p-doped chemiresistive film. The adsorption phenomenon slows down the recovery time of the ammonium sensor. This sensor design is a new platform to continuously monitor ions in industrial, domestic, and environmental water resources by robust chemiresistive devices.

Universal Fully Integrated Wearable Sensor Arrays for the Multiple Electrolyte and Metabolite Monitoring in Raw Sweat, Saliva, or Urine

Fully integrated wearable sensors are capable of dynamically, directly, and independently tracking biomarkers in raw noninvasive biofluids without any other equipment or accessories by integrating the unique on-body monitoring feature with the special complete functional implementation attribute. Sweat, saliva, and urine are three important noninvasive biofluids, and changes in their biomarkers hold great potential for revealing physiological conditions. However, it is still a challenge to design single fully integrated wearable sensor arrays (FIWSAs) that are universally able to concurrently measure electrolytes and metabolites in three of the most common noninvasive biofluids including sweat, saliva, and urine. Here, we propose the first single universal FIWSAs for wirelessly, noninvasively, and simultaneously measuring various metabolites (i.e., uric acid) and electrolytes (i.e., Na⁺ and H⁺) in raw sweat, saliva, or urine under subjects' exercise by integrating the specifically designed microfluidic, sensing, and electronic modules in a seamless manner. We evaluate its utility for noninvasive gout management in healthy subjects and in gout patients through a purine-rich meal challenge and with a medicine-treatment control, respectively. Noninvasive monitoring of multiple electrolytes and metabolites in a variety of raw noninvasive biofluids via such single universal FIWSAs may enrich the understanding of the biomarkers' levels in the body and would also facilitate self-health management.

Overview of Engineering Carbon Nanomaterials Such As Carbon Nanotubes (CNTs), Carbon Nanofibers (CNFs), Graphene and Nanodiamonds and Other Carbon Allotropes inside Porous Anodic Alumina (PAA) Templates

The fabrication and design of carbon-based hierarchical structures with tailored nano-architectures have attracted the enormous attention of the materials science community due to their exceptional chemical and physical properties. The collective control of nano-objects, in terms of their dimensionality, orientation and size, is of paramount importance to expand the implementation of carbon nanomaterials across a large variety of applications. In this context, porous anodic alumina (PAA) has become an attractive template where the pore morphologies can be straightforwardly modulated. The synthesis of diverse carbon nanomaterials can be performed using PAA templates, such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and nanodiamonds, or can act as support for other carbon allotropes such as graphene and other carbon nanoforms. However, the successful growth of carbon nanomaterials within ordered PAA templates typically requires a series of stages involving the template fabrication, nanostructure growth and finally an etching or electrode metallization steps, which all encounter different challenges towards a nanodevice fabrication. The present review article describes the advantages and challenges associated with the fabrication of carbon materials in PAA based materials and aims to give a renewed momentum to this topic within the materials science community by providing an exhaustive overview of the current synthesis approaches and the most relevant applications based on PAA/Carbon nanostructures materials. Finally, the perspective and opportunities in the field are presented.

Activity-Dependent Fluctuations in Interstitial [K+]: Investigations Using Ion-Sensitive Microelectrodes

In the course of action potential firing, all axons and neurons release K⁺ from the intra- cellular compartment into the interstitial space to counteract the depolarizing effect of Na⁺ influx, which restores the resting membrane potential. This efflux of K⁺ from axons results in K⁺ accumulation in the interstitial space, causing depolarization of the K⁺ reversal potential (E_K), which can prevent subsequent action potentials. To ensure optimal neuronal function, the K⁺ is buffered by astrocytes, an energy-dependent process, which acts as a sink for interstitial K⁺, absorbing it at regions of high concentration and distributing it through the syncytium for release in distant regions. Pathological processes in which energy production is compromised, such as anoxia, ischemia, epilepsy and spreading depression, can lead to excessive interstitial K⁺ accumulation, disrupting sensitive trans-membrane ion gradients and attenuating neuronal activity. The changes that occur in interstitial [K⁺] resulting from both physiological and pathological processes can be monitored accurately in real time using K⁺-sensitive microelectrodes, an invaluable tool in electrophysiological studies.

Biosensors: Electrochemical Devices-General Concepts and Performance

This review provides a general overview of different biosensors, mostly concentrating on electrochemical analytical devices, while briefly explaining general approaches to various kinds of biosensors, their construction and performance. A discussion on how all required components of biosensors are brought together to perform analytical work is offered. Different signal-transducing mechanisms are discussed, particularly addressing the immobilization of biomolecular components in the vicinity of a transducer interface and their functional integration with electronic devices. The review is mostly addressing general concepts of the biosensing processes rather than specific modern achievements in the area.

A Bifunctional Fully Integrated Wearable Tracker for Epidermal Sweat and Wound Exudate Multiple Biomarkers Monitoring

Fully integrated wearable electronics that combine the extraordinary feature of incessant and on-body operation with the distinctive external equipment-free trait are the ultimate goal of modern wearables. Epidermal sweat and wound exudate, as two noninvasively accessible biofluids on/surrounding the skin, reflect underlying health conditions. However, the design of universal wearable sensors with the bifunctional capability to monitor both epidermal secretions is still a challenge. Here, a single bifunctional fully integrated wearable tracker for wirelessly, simultaneously, and dynamically in situ measuring multiple epidermal sweat or wound exudate biomarkers is propos. Considering the electrolytes (e.g., Na⁺ , K⁺ , and H⁺ ) and metabolites (e.g., uric acid (UA)) levels in sweat or wound exudate may correlate with health or wound conditions, the dynamic and skin-on tracking of the biomarkers of Na⁺ , K⁺ , pH, and UA levels in sweat under subjects' exercise and in wound exudate during subjects' wound healing are performed through the seamless integration of microfluidic, sensing, and electronic modules. Its applicability is evaluated for noninvasive hyperuricemia management in hyperuricemia/healthy subjects through a purine-rich intake test and for wound management in subjects' infected wounds through a control medical treatment.

Materials discovery of ion-selective membranes using artificial intelligence

Significant attempts have been made to improve the production of ion-selective membranes (ISMs) with higher efficiency and lower prices, while the traditional methods have drawbacks of limitations, high cost of experiments, and time-consuming computations. One of the best approaches to remove the experimental limitations is artificial intelligence (AI). This review discusses the role of AI in materials discovery and ISMs engineering. The AI can minimize the need for experimental tests by data analysis to accelerate computational methods based on models using the results of ISMs simulations. The coupling with computational chemistry makes it possible for the AI to consider atomic features in the output models since AI acts as a bridge between the experimental data and computational chemistry to develop models that can use experimental data and atomic properties. This hybrid method can be used in materials discovery of the membranes for ion extraction to investigate capabilities, challenges, and future perspectives of the AI-based materials discovery, which can pave the path for ISMs engineering.

Recent Literature Review of Significance of Polypyrrole and Its Biocomposites in Adsorption of Dyes from Aqueous Solution

The usage of dyes has been tremendously augmented due to industrialization and human’s intrinsic fascination with colors. Owing to their excessive usage in industries like textiles, food, cosmetics, paints, printing etc., it is indisputably a contributing factor in aquatic pollution. Dyes effluents have emerged as a burgeoning challenge. Owing to issues such as toxicity, mutagenicity, and disturbed photosynthesis associated with dye contamination, it is crucial to look for an explication to deal with this challenge. Polypyrrole-based biocomposites have been reported as good adsorbents for textile wastewater treatment. In the last decade, numerous studies have stated the effective removal of dyes via Polypyrrole-based biocomposites. This review concentrates on the implication of different Polypyrrole-based biocomposites for decontamination of dyes and synthesis methods, characteristics, and mechanism of dyes degradation by these biocomposites from wastewater.

Ion-Selective Organic Electrochemical Transistors: Recent Progress and Challenges

The charged species inside biofluids (blood, interstitial fluid, sweat, saliva, urine, etc.) can reflect the human body's physiological conditions and thus be adopted to diagnose various diseases early. Among all personalized health management applications, ion-selective organic electrochemical transistors (IS-OECTs) have shown tremendous potential in point-of-care testing of biofluids due to low cost, ease of fabrication, high signal amplification, and low detection limit. Moreover, IS-OECTs exhibit excellent flexibility and biocompatibility that enable their application in wearable bioelectronics for continuous health monitoring. In this review, the working principle of IS-OECTs and the recent studies of IS-OECTs for performance improvement are reviewed. Specifically, contemporary studies on material design and device optimization to enhance the sensitivity of IS-OECTs are discussed. In addition, the progress toward the commercialization of IS-OECTs is highlighted, and the recently proposed solutions or alternatives are summarized. The main challenges and perspectives for fully exploiting IS-OECTs toward future preventive and personal medical devices are addressed.

Recent advances in polymeric nanostructured ion selective membranes for biomedical applications

Nano structured ion-selective membranes (ISMs) are very attractive materials for a wide range of sensing and ion separation applications. The present review focuses on the design principles of various ISMs; nanostructured and ionophore/ion acceptor doped ISMs, and their use in biomedical engineering. Applications of ISMs in the biomedical field have been well-known for more than half a century in potentiometric analysis of biological fluids and pharmaceutical products. However, the emergence of nanotechnology and sophisticated sensing methods assisted in miniaturising ion-selective electrodes to needle-like sensors that can be designed in the form of implantable or wearable devices (smartwatch, tattoo, sweatband, fabric patch) for health monitoring. This article provides a critical review of recent advances in miniaturization, sensing and construction of new devices over last decade (2011-2021). The designing of tunable ISM with biomimetic artificial ion channels offered intensive opportunities and innovative clinical analysis applications, including precise biosensing, controlled drug delivery and early disease diagnosis. This paper will also address the future perspective on potential applications and challenges in the widespread use of ISM for clinical use. Finally, this review details some recommendations and future directions to improve the accuracy and robustness of ISMs for biomedical applications.

Spectroelectrochemical Evidence of Interconnected Charge and Ion Transfer in Ultrathin Membranes Modulated by a Redox Conducting Polymer

Previous publications have demonstrated the tuning of ion-transfer (IT) processes across ion-selective membranes (ISMs) with thicknesses in the nanometer order by modulating the oxidation state of a film of a conducting polymer, such as poly(3-octylthiophene) [POT], that is in back-side contact. Attempts on the theoretical description of this charge transfer (CT)-IT system have considered the Nernst equation for the CT, while there is no empirical evidence confirming this behavior. We present herein the first experimental characterization of the CT in POT films involved in different CT-IT systems. We take advantage of the absorbance change in the POT film while being oxidized, to monitor the CT linked to nonassisted and assisted ITs at the sample-ISM interface, from one to three ionophores, therefore promoting a change in the nature and number of the ITs. The CT is visualized as an independent sigmoid in different potential ranges according to the assigned IT. Herein, we have proposed a simple calculation of the empirical CT utilizing the mathematical Sigmoidal-Boltzmann model. The identification of the physical meaning of the mathematical definition of CT opens up new possibilities for the design of sensors with superior analytical features (mainly in terms of selectivity) and the calculation of apparent binding constants in the ISM.

Advances in Sweat Wearables: Sample Extraction, Real-Time Biosensing, and Flexible Platforms

Wearable biosensors for sweat-based analysis are gaining wide attention due to their potential use in personal health monitoring. Flexible wearable devices enable sweat analysis at the molecular level, facilitating noninvasive monitoring of physiological states via real-time monitoring of chemical biomarkers. Advances in sweat extraction technology, real-time biosensors, stretchable materials, device integration, and wireless digital technologies have led to the development of wearable sweat-biosensing devices that are light, flexible, comfortable, aesthetic, affordable, and informative. Herein, we summarize recent advances of sweat wearables from the aspects of sweat extraction, fabrication of stretchable biomaterials, and design of biosensing modules to enable continuous biochemical monitoring, which are essential for a biosensing device. Key chemical components of sweat, sweat capture methodologies, and considerations of flexible substrates for integrating real-time biosensors with electronics to bring innovations in the art of wearables are elaborated. The strategies and challenges involved in improving the wearable biosensing performance and the perspectives for designing sweat-based wearable biosensing devices are discussed.

Recent advances in solid-contact ion-selective electrodes: functional materials, transduction mechanisms, and development trends

This article presents a comprehensive overview of recent progress in the design and applications of solid-contact ion-selective electrodes (SC-ISEs).