Biosensors-Recent Advances and Future Challenges in Electrode Materials

A life cycle assessment approach to minimize environmental impact for sustainable printed sensors

A printed hybrid sensor tag for applications in disposable healthcare and environmental monitoring optimized toward sustainability is presented. Following a systematic Life Cycle Assessment according to ISO 14040:2006 guidelines, the global warming potential associated with various substrate-, electrode-, and sensing materials, as well as manufacturing and end-of-life strategies, are evaluated. Results show that the utilization of bio-based polyethylene and copper inks can minimize the global warming potential most effectively by up to 39% from 42gCO2eq to 25.7gCO2eq per sensor tag. Among manufacturing methods, screen printing coupled with intense pulse light curing emerges as the most eco-efficient combination. Recycling is the most sustainable end-of-life option, although infrastructure challenges impede its full implementation. The silicon sensor chip needed for data communication has been identified as environmental hotspot. This study offers a comprehensive environmental evaluation of sustainable printed sensors and highlights critical challenges and opportunities for the electronics industry, particularly in relation to material selection, recycling strategies, and system-level considerations.

Applications and prospects of biomaterials in diabetes management

Diabetes is a widespread metabolic disorder that presents considerable challenges in its management. Recent advancements in biomaterial research have shed light on innovative approaches for the treatment of diabetes. This review examines the role of biomaterials in diabetes diagnosis and treatment, as well as their application in managing diabetic wounds. By evaluating recent research developments alongside future obstacles, the review highlights the promising potential of biomaterials in diabetes care, underscoring their importance in enhancing patient outcomes and refining treatment methodologies.

Interplay of Surface Charge and Pore Characteristics in the Immobilization of Lactate Oxidase on Bulk Nanoporous Gold Electrodes

Immobilization of enzymes on (nano)porous metal carriers provides the foundation for an advanced design of bioelectrodes suitable for catalysis and sensing. However, interactions upon adsorption are still poorly understood, and so the efficient coupling of the enzymes to the electrode surface remains one of the major challenges. Here, we present a comprehensive study of the immobilization behavior of Aerococcus viridans l-lactate oxidase (LOx) on nanoporous gold (npAu) in dependence of electrode modification with differently charged self-assembled monolayers (SAMs). The highest activity (up to 14 U/g) and electrocatalytic response (sensitivity of 3.9 μA mM-1) were observed for a sulfonate-terminated SAM. This is contrary to enzyme behavior on conventional polymer carriers, and thus, the effect is specific to the metal electrodes. We propose the capture of the negatively charged LOx in a dense counterion layer in close proximity to the strongly negatively charged gold surface. Adsorption on positively charged amine-terminated SAMs resulted in a similar immobilization yield but gave much lower activity (4-fold). Importantly, the effect of the sulfonate SAM was strongly dependent on the npAu electrode pore size: the highest LOx activity (in U/cm2) was found with pores (diameter of ∼170 nm) supposedly large enough to facilitate enzyme diffusion into the porous structure during immobilization. Electrochemical sensing of H2O2 produced by the LOx reaction showed a 2.5-fold higher sensitivity for l-lactate on the negatively charged surface. Lixiviation studies supported the proposed layer capture and revealed a faster decline in the electrode activity with sulfonate surface modification. Collectively, the present study reveals enhanced activity of LOx on sulfonate-charged gold surfaces and a strong pore size dependence. These findings deepen the understanding of the immobilization behavior of LOx on charged nanoporous metals and have importance for the advanced design of enzyme electrodes.

Electrochemical methods for evaluation of therapeutic monoclonal antibodies: A review

Biopharmaceuticals are complex pharmaceutical drug products produced by biotechnology in living systems. Small changes in the production process can induce differences in the structure of the active ingredient, which may have a strong impact on its pharmacological properties. Therefore, quality assurance of biopharmaceuticals results in a high analytical effort. Strict quality and stability monitoring of potentially critical quality attributes (CQAs) is required. Electrochemical methods have been contributing to the expansion of sensors and biosensors due to their advantages, such as cost-effectiveness and easy operation. Here, we discuss the recent developments in sensors and biosensors using electrochemical techniques employed for the determination of biopharmaceuticals, namely monoclonal antibodies (mAb) and fragments of mAbs. In the frame of this information, this review aims to critically address electrochemical sensors and biosensors for the analysis of biopharmaceuticals reported since 2016. Electrochemical bio(sensors) development has been mainly based on gold and aptamers, respectively, as the most used electrode material and biorecognition element. Also, Bevacizumab (BEVA) was the main therapeutic mAb detected and 69% of the works described a (bio)sensor) that can be applied to therapeutic drug monitoring.

Electrochemically Induced Nanoscale Stirring Boosts Functional Immobilization of Flavocytochrome P450 BM3 on Nanoporous Gold Electrodes

Enzyme-modified electrodes are core components of electrochemical biosensors for diagnostic and environmental analytics and have promising applications in bioelectrocatalysis. Despite huge research efforts spanning decades, design of enzyme electrodes for superior performance remains challenging. Nanoporous gold (npAu) represents advanced electrode material due to high surface-to-volume ratio, tunable porosity, and intrinsic redox activity, yet its coupling with enzyme catalysis is complex. Here, the study reports a flexible-modular approach to modify npAu with functional enzymes by combined material and protein engineering and use a tailored assortment of surface and in-solution methodologies for characterization. Self-assembled monolayer (SAM) of mercaptoethanesulfonic acid primes the npAu surface for electrostatic adsorption of the target enzyme (flavocytochrome P450 BM3; CYT102A1) that is specially equipped with a cationic protein module for directed binding to anionic surfaces. Modulation of the SAM surface charge is achieved by electrochemistry. The electrode-adsorbed enzyme retains well the activity (33%) and selectivity (complete) from in-solution. Electrochemically triggered nanoscale stirring in the internal porous network of npAu-SAM enhances speed (2.5-fold) and yield (3.0-fold) of the enzyme immobilization. Biocatalytic reaction is fueled from the electrode via regeneration of its reduced coenzyme (NADPH). Collectively, the study presents a modular design of npAu-based enzyme electrode that can support flexible bioelectrochemistry applications.

Biosensors for early stroke detection

This article aims to provide a comprehensive review of the latest advances in biosensor technology for early stroke diagnosis. Analyzing current research from authoritative databases highlights the significance of biosensors in improving stroke detection and treatment outcomes, discusses their diagnostic capabilities, and addresses the challenges that must be overcome for broader clinical application. This review utilizes updated information and valid research from ISI, Google Scholar, Science Direct, Scopus, and PubMed to examine recent developments in biosensors applicable to early stroke diagnosis. The results indicate that biosensors are crucial for the early detection of strokes, and enhance treatment efficacy. The biosensors studied in this research serve as rapid and non-intrusive diagnostic instruments with exceptional precision and detection capabilities. Cutting-edge biosensors can identify distinct stroke-related biomarkers, offering rapid and non-invasive diagnostic solutions to improve stroke care outcomes. Despite these advancements, significant challenges remain regarding the sensitivity, specificity, and reliability of biosensors. These issues must be resolved to facilitate their widespread implementation in clinical settings.

Electrochemical biosensors in early detection of Parkinson disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder affecting the motor system, with symptoms including tremors, rigidity, bradykinesia, and postural instability. Affecting over six million people globally, PD's pathophysiology is marked by the loss of dopaminergic neurons in the substantia nigra. Early diagnosis is crucial for effective management, yet current methods are limited by low sensitivity, high cost, and the need for advanced equipment. Electrochemical biosensors have emerged as promising tools for early PD diagnosis, converting biological reactions into measurable electrical signals for evaluating PD biomarkers. Advances in nanotechnology and material science have led to innovative sensing platforms with enhanced sensitivity and selectivity. Key biomarkers such as alpha-synuclein (α-syn), dopamine (DA), and microRNAs (miRNAs) have been targeted using these biosensors. For instance, gold nanoparticle-modified graphene immunosensors have shown ultra-sensitive detection of α-syn, while graphene-based biosensors have demonstrated high sensitivity for DA detection. Additionally, nanobiosensors for miR-195 and electrochemical aptasensors have shown potential for early PD diagnosis. The integration of nanomaterials like gold nanoparticles, quantum dots, and carbon nanotubes has further advanced the field, enhancing electrochemical activity and sensitivity. These developments offer a reliable, rapid, and cost-effective approach for early PD diagnosis, paving the way for better management and treatment. Continued research is essential for the commercialization and clinical integration of these biosensors, ultimately improving patient outcomes.

How can heteroatoms boost the performance of photoactive nanomaterials for wastewater purification?

Photocatalysis, as an alternative for treating persistent water pollutants, holds immense promise. However, limitations hinder sustained treatment and recycling under varying light conditions. This comprehensive review delves into the novel paradigm of metal and non-metal doping to overcome these challenges. It begins by discussing the fundamental principles of photocatalysis and its inherent limitations. Understanding these constraints is crucial for developing effective strategies. Band gap narrowing by metal and non-metal doping modifies the band gap, enabling visible-light absorption. Impurity energy levels and oxygen vacancies influenced the doping energy levels and surface defects. Interfacial electron transfer and charge carrier recombination are the most important factors that impact overall efficiency. The comparative analysis of nanomaterials are reviewed on various, including nanometal oxides, nanocarbon materials, and advanced two-dimensional structures. The synthesis process are narratively presented, emphasizing production yields, selectivity, and efficiency. The review has potential applications in the environment for efficient pollutant removal and water purification, economic cost-effective and scalable production and technological advancement catalyst design, in spite of its challenges in material stability, synthesis methods and optimizing band gaps. The novelty of the review paper is on the proposal of a new paradigm of heterojunctions of doped metal and non-metal photocatalysts to promise highly efficient water treatment. This review bridges the gap between fundamental research and practical applications, offering insights into tailored nano photocatalysts.

Development of a label-free, sensitive gold nanoparticles-poly(adenine) aptasensing platform for colorimetric determination of aflatoxin B1 in corn

In this work, a sensitive colorimetric bioassay method based on a poly(adenine) aptamer (polyA apt) and gold nanoparticles (AuNPs) was developed for the determination of aflatoxin B1 (AFB1). The polyA apt, adsorbed on the AuNPs, especially can bind to the analyte while deterring non-specific interactions. This nano aptasensor uses cationic polymer poly(diallyl dimethyl ammonium chloride) (PDDA), as an aggregating agent, to aggregate gold nanoparticles. PolyA apt-decorated gold nanoparticles (AuNPs/polyA apt) show resistance to PDDA-induced aggregation and maintains their dispersed state (red color) with the optical absorbance signal at λ = 520 nm. However, in the presence of AFB1 in the assay solution, the specific aptamer reacts with high affinity and folds into its three-dimensional form. Aggregation of AuNPs induced by PDDA caused their optical signal shift to λ = 620 nm (blue color). AFB1 concentration in the bioassay solution determines the amount of optical signal shift. Therefore, optical density ratio in two wavelengths (A620/520) can be used as a sturdy colorimetric signal to detect the concentration of aflatoxin B1. AFB1 was linearly detected between 0.5 and 20 ng mL-1, with a detection limit of 0.09 ng mL-1 (S/N = 3). The fabricated aptasensor was applied to the detection of AFB1 in real corn samples.

Electrochemical Detection of Bisphenol A Based on Gold Nanoparticles/Multi-Walled Carbon Nanotubes: Applications on Glassy Carbon and Screen Printed Electrodes

Bisphenol A (BPA) has been classified as an endocrine-disrupting substance that may cause adverse effects on human health and the environment. The development of simple and sensitive electrochemical biosensors is crucial for the rapid and effective quantitative determination of BPA. This work presents a study on electrochemical sensors utilizing gold nanoparticle-modified multi-walled carbon nanotubes (CNT/AuNPs). Glassy carbon electrodes (GCEs) and screen-printed electrodes (SPEs) were conveniently modified and used for BPA detection. AuNPs were electrodeposited onto the CNT-modified electrodes using the galvanostatic method. The electrodes were properly modified and characterized by using Raman spectroscopy, cyclic voltammetry (CV), and electrochemical impedance analysis (EIS). The electrochemical response of the sensors was studied using differential pulse voltammetry (DPV) and constant potential amperometry (CPA) for modified GCE and SPE electrodes, respectively, and the main analytical parameters were studied and optimized. Problems encountered with the use of GCEs, such as sensor degradation and high limit of detection (LOD), were overcome by using modified SPEs and a flow injection device for the measurements. Under this approach, an LOD as low as 5 nM (S/N = 3) was achieved and presented a linear range up to 20 μM. Finally, our investigation addressed interference, reproducibility, and reusability aspects, successfully identifying BPA in both spiked and authentic samples, including commercial and tap waters. These findings underscore the practical applicability of our method for accurate BPA detection in real-world scenarios. Notably, the integration of SPEs and a flow injection device facilitated simplified automation, offering an exceptionally efficient and reliable solution for precise BPA detection in water analysis laboratories.

Continuous and Non-Invasive Lactate Monitoring Techniques in Critical Care Patients

Lactate, once merely regarded as an indicator of tissue hypoxia and muscular fatigue, has now gained prominence as a pivotal biomarker across various medical disciplines. Recent research has unveiled its critical role as a high-value prognostic marker in critical care medicine. The current practice of lactate detection involves periodic blood sampling. This approach is invasive and confined to measurements at six-hour intervals, leading to resource expenditure, time consumption, and patient discomfort. This review addresses non-invasive sensors that enable continuous monitoring of lactate in critical care patients. After the introduction, it discusses the iontophoresis system, followed by a description of the structural materials that are universally employed to create an interface between the integumentary system and the sensor. Subsequently, each method is detailed according to its physical principle, outlining its advantages, limitations, and pertinent aspects. The study concludes with a discussion and conclusions, aiming at the design of an intelligent sensor (Internet of Medical Things or IoMT) to facilitate continuous lactate monitoring and enhance the clinical decision-making support system in critical care medicine.

Hybrid Impedimetric Biosensors for Express Protein Markers Detection

Impedimetric biosensors represent a powerful and promising tool for studying and monitoring biological processes associated with proteins and can contribute to the development of new approaches in the diagnosis and treatment of diseases. The basic principles, analytical methods, and applications of hybrid impedimetric biosensors for express protein detection in biological fluids are described. The advantages of this type of biosensors, such as simplicity and speed of operation, sensitivity and selectivity of analysis, cost-effectiveness, and an ability to be integrated into hybrid microfluidic systems, are demonstrated. Current challenges and development prospects in this area are analyzed. They include (a) the selection of materials for electrodes and formation of nanostructures on their surface; (b) the development of efficient methods for biorecognition elements' deposition on the electrodes' surface, providing the specificity and sensitivity of biosensing; (c) the reducing of nonspecific binding and interference, which could affect specificity; (d) adapting biosensors to real samples and conditions of operation; (e) expanding the range of detected proteins; and, finally, (f) the development of biosensor integration into large microanalytical system technologies. This review could be useful for researchers working in the field of impedimetric biosensors for protein detection, as well as for those interested in the application of this type of biosensor in biomedical diagnostics.

Innovative Biosensing Approaches for Swift Identification of Candida Species, Intrusive Pathogenic Organisms

Candida is the largest genus of medically significant fungi. Although most of its members are commensals, residing harmlessly in human bodies, some are opportunistic and dangerously invasive. These have the ability to cause severe nosocomial candidiasis and candidemia that affect the viscera and bloodstream. A prompt diagnosis will lead to a successful treatment modality. The smart solution of biosensing technologies for rapid and precise detection of Candida species has made remarkable progress. The development of point-of-care (POC) biosensor devices involves sensor precision down to pico-/femtogram level, cost-effectiveness, portability, rapidity, and user-friendliness. However, futuristic diagnostics will depend on exploiting technologies such as multiplexing for high-throughput screening, CRISPR, artificial intelligence (AI), neural networks, the Internet of Things (IoT), and cloud computing of medical databases. This review gives an insight into different biosensor technologies designed for the detection of medically significant Candida species, especially Candida albicans and C. auris, and their applications in the medical setting.

The Use of Crystalline Carbon-Based Nanomaterials (CBNs) in Various Biomedical Applications

This review study aims to present, in a condensed manner, the significance of the use of crystalline carbon-based nanomaterials in biomedical applications. Crystalline carbon-based nanomaterials, encompassing graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, and graphene quantum dots, have emerged as promising materials for the development of medical devices in various biomedical applications. These materials possess inorganic semiconducting attributes combined with organic π-π stacking features, allowing them to efficiently interact with biomolecules and present enhanced light responses. By harnessing these unique properties, carbon-based nanomaterials offer promising opportunities for future advancements in biomedicine. Recent studies have focused on the development of these nanomaterials for targeted drug delivery, cancer treatment, and biosensors. The conjugation and modification of carbon-based nanomaterials have led to significant advancements in a plethora of therapies and have addressed limitations in preclinical biomedical applications. Furthermore, the wide-ranging therapeutic advantages of carbon nanotubes have been thoroughly examined in the context of biomedical applications.

Opportunities and challenges for sweat-based monitoring of metabolic syndrome via wearable technologies

Metabolic syndrome is a prevalent condition in adults over the age of 65 and is a risk factor for developing cardiovascular disease and type II diabetes. Thus, methods to track the condition, prevent complications and assess symptoms and risk factors are needed. Here we discuss sweat-based wearable technologies as a potential monitoring tool for patients with metabolic syndrome. We describe several key symptoms that can be evaluated that could employ sweat patches to assess inflammatory markers, glucose, sodium, and cortisol. We then discuss the challenges with material property, sensor integration, and sensor placement and provide feasible solutions to optimize them. Together with a list of recommendations, we propose a pathway toward successfully developing and implementing reliable sweat-based technologies to monitor metabolic syndrome.

Metabolic syndrome is a risk factor for developing cardiovascular disease and type II diabetes. Lyzwinski, Elgendi and colleagues discuss the potential role of sweat-based wearable technologies for monitoring metabolic syndrome along with engineering challenges towards implementation and optimization

Electrochemical, optical and mass-based immunosensors: A comprehensive review of Bacillus anthracis detection methods

A biosensor is an analytical device whose main components include transducer and bioreceptor segments. The combination of biological recognition with the ligand is followed by transformation into physical or chemical signals. Many publications describe biological sensors as user-friendly, easy, portable, and less time-consuming than conventional methods. Among major categories of methods for the detection of Bacillus anthracis, such as culture-based microbiological method, polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA), microarray-based techniques sensors with bioreceptors have been highlighted which particular emphasis is placed on herein. There are several types of biosensors based on various chemical or physical transducers (e.g., electrochemical, optical, piezoelectric, thermal or magnetic electrodes) and the type of biological materials used (e.g., enzymes, nucleic acids, antibodies, cells, phages or tissues). In recent decades, antibody-based sensors have increasingly gained popularity due to their reliability, sensitivity and rapidness. The fundamental principle of antibody-based sensors is mainly based on the molecular recognition between antigens and antibodies. Therefore, immunosensors that detect B. anthracis surface antigens can provide a rapid tool for detecting anthrax bacilli and spores, especially in situ. This review provides a comprehensive summary of immunosensor-based methods using electrochemical, optical, and mass-based transducers to detect B. anthracis.

Interdomain Linker of the Bioelecrocatalyst Cellobiose Dehydrogenase Governs the Electron Transfer

Direct bioelectrocatalysis applied in biosensors, biofuel cells, and bioelectrosynthesis is based on an efficient electron transfer between enzymes and electrodes in the absence of redox mediators. Some oxidoreductases are capable of direct electron transfer (DET), while others achieve the enzyme to electrode electron transfer (ET) by employing an electron-transferring domain. Cellobiose dehydrogenase (CDH) is the most-studied multidomain bioelectrocatalyst and features a catalytic flavodehydrogenase domain and a mobile, electron-transferring cytochrome domain connected by a flexible linker. The ET to the physiological redox partner lytic polysaccharide monooxygenase or, ex vivo, electrodes depends on the flexibility of the electron transferring domain and its connecting linker, but the regulatory mechanism is little understood. Studying the linker sequences of currently characterized CDH classes we observed that the inner, mobile linker sequence is flanked by two outer linker regions that are in close contact with the adjacent domain. A function-based definition of the linker region in CDH is proposed and has been verified by rationally designed variants of Neurospora crassa CDH. The effect of linker length and its domain attachment on electron transfer rates has been determined by biochemical and electrochemical methods, while distances between the domains of CDH variants were computed. This study elucidates the regulatory mechanism of the interdomain linker on electron transfer by determining the minimum linker length, observing the effects of elongated linkers, and testing the covalent stabilization of a linker part to the flavodehydrogenase domain. The evolutionary guided, rational design of the interdomain linker provides a strategy to optimize electron transfer rates in multidomain enzymes and maximize their bioelectrocatalytic performance.

Highly responsive and sensitive non-enzymatic electrochemical sensor for the detection of β-NADH in food, environmental and biological samples using AuNP on polydopamine/titanium carbide composite

In this study, a polydopamine/titanium carbide adorned with gold nanoparticles (Au@PDA/TiC) composite was prepared by a simple stirring technique and it was used for the dual-technique detection of β-Nicotinamide adenine dinucleotide (NADH). The Au@PDA/TiC-modified glassy carbon electrode (GCE) oxidized NADH at a very low oxidation potential of approximately 0.60 V vs Ag/AgCl in pH = 7.0 (0.1 M PBS) via the transfer of two electrons and one proton (from NADH to NAD⁺). Based on the (i-t) amperometry mode, NADH can be quantified with a linear range of 0.018-674 μM and LOD of 0.0062 µM. In addition to the DPV mode, the electrochemical sensor had a linearity of 5-450 µM with a LOD of 3.17 µM. The developed sensor exhibited remarkable analytical performances concerning high sensitivity, electrocatalytic activity, low detection limit, wide linearity, appreciable specificity, repeatability, stability, reproducibility, and adequate recovery results in food, environmental and biological samples.

Biomarkers as Biomedical Bioindicators: Approaches and Techniques for the Detection, Analysis, and Validation of Novel Biomarkers of Diseases

A biomarker is any measurable biological moiety that can be assessed and measured as a potential index of either normal or abnormal pathophysiology or pharmacological responses to some treatment regimen. Every tissue in the body has a distinct biomolecular make-up, which is known as its biomarkers, which possess particular features, viz., the levels or activities (the ability of a gene or protein to carry out a particular body function) of a gene, protein, or other biomolecules. A biomarker refers to some feature that can be objectively quantified by various biochemical samples and evaluates the exposure of an organism to normal or pathological procedures or their response to some drug interventions. An in-depth and comprehensive realization of the significance of these biomarkers becomes quite important for the efficient diagnosis of diseases and for providing the appropriate directions in case of multiple drug choices being presently available, which can benefit any patient. Presently, advancements in omics technologies have opened up new possibilities to obtain novel biomarkers of different types, employing genomic strategies, epigenetics, metabolomics, transcriptomics, lipid-based analysis, protein studies, etc. Particular biomarkers for specific diseases, their prognostic capabilities, and responses to therapeutic paradigms have been applied for screening of various normal healthy, as well as diseased, tissue or serum samples, and act as appreciable tools in pharmacology and therapeutics, etc. In this review, we have summarized various biomarker types, their classification, and monitoring and detection methods and strategies. Various analytical techniques and approaches of biomarkers have also been described along with various clinically applicable biomarker sensing techniques which have been developed in the recent past. A section has also been dedicated to the latest trends in the formulation and designing of nanotechnology-based biomarker sensing and detection developments in this field.

Integration of nanomaterial sensing layers on printable organic field effect transistors for highly sensitive and stable biochemical signal conversion

Organic field effect transistor (OFET) devices are one of the most popular candidates for the development of biochemical sensors due to their merits of being flexible and highly customizable for low-cost large-area manufacturing. This review describes the key points in constructing an extended-gate type OFET (EGOFET) biochemical sensor with high sensitivity and stability. The structure and working mechanism of OFET biochemical sensors are described firstly, emphasizing the importance of critical material and device engineering to higher biochemical sensing capabilities. Next, printable materials used to construct sensing electrodes (SEs) with high sensitivity and stability are presented with a focus on novel nanomaterials. Then, methods of obtaining printable OFET devices with steep subthreshold swing (SS) for high transconductance efficiency are introduced. Finally, approaches for the integration of OFETs and SEs to form portable biochemical sensor chips are introduced, followed by several demonstrations of sensory systems. This review will provide guidelines for optimizing the design and manufacturing of OFET biochemical sensors and accelerating the movement of OFET biochemical sensors from the laboratory to the marketplace.

TEER and Ion Selective Transwell-Integrated Sensors System for Caco-2 Cell Model

Monitoring of ions in real-time directly in cell culture systems and in organ-on-a-chip platforms represents a significant investigation tool to understand ion regulation and distribution in the body and ions' involvement in biological mechanisms and specific pathologies. Innovative flexible sensors coupling electrochemical stripping analysis (square wave anodic stripping voltammetry, SWASV) with an ion selective membrane (ISM) were developed and integrated in Transwell™ cell culture systems to investigate the transport of zinc and copper ions across a human intestinal Caco-2 cell monolayer. The fabricated ion-selective sensors demonstrated good sensitivity (1 × 10^-11 M ion concentration) and low detection limits, consistent with pathophysiological cellular concentration ranges. A non-invasive electrochemical impedance spectroscopy (EIS) analysis, in situ, across a selected spectrum of frequencies (10-10⁵ Hz), and an equivalent circuit fitting were employed to obtain useful electrical parameters for cellular barrier integrity monitoring. Transepithelial electrical resistance (TEER) data and immunofluorescent images were used to validate the intestinal epithelial integrity and the permeability enhancer effect of ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) treatment. The proposed devices represent a real prospective tool for monitoring cellular and molecular events and for studies on gut metabolism/permeability. They will enable a rapid integration of these sensors into gut-on-chip systems.

Applications of Nanoporous Gold in Therapy, Drug Delivery, and Diagnostics

Nanoporous gold (np-Au) has promising applications in therapeutic delivery. The promises arise from its high surface area-to-volume ratio, ease of tuning shape and size, ability to be modified by organic molecules including drugs, and biocompatibility. Furthermore, np-Au nanostructures can generate the photothermal effect. This effect can be used either for controlled release of drugs of therapeutic importance or for destroying cancer cells by heating locally. Despite the enormous potential, the research on the therapeutical use of the np-Au is still in its early stage. In this review, we discuss the current progress and future directions of np-Au for therapeutic applications.

Cleaning of LTCC, PEN, and PCB Au electrodes towards reliable electrochemical measurements

Surface cleaning of the working electrode has a key role in improved electrochemical and physicochemical properties of the biosensors. Herein, chemical oxidation in piranha, chemical cleaning in potassium hydroxide-hydrogen peroxide, combined (electro-) chemical alkaline treatment, and potential cycling in sulfuric acid were applied to gold finish electrode surfaces deposited onto three different substrates; low temperature co-fired ceramics (LTCC), polyethylene naphthalate (PEN), and polyimide (PI), using three different deposition technologies; screen printing, inkjet printing, and electroplating (printed circuit board technology, PCB) accordingly. The effects of the (electro-) chemical treatments on the gold content and electrochemical responses of LTCC, PEN, and PCB applicable for aptamer-based sensors are discussed. In order to assess the gold surface and to compare the efficiency of the respective cleaning procedures; cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were employed. LTCC sensors electrochemically cycled in sulfuric acid resulted in the most gold content on the electrode surface, the lowest peak potential difference, and the highest charge transfer ability. While, for PEN, the highest elemental gold and the lowest peak-to-peak separation were achieved by a combined (electro-) chemical alkaline treatment. Gold content and electrochemical characteristics on the PCB surface with extremely thin gold layer could be slightly optimized with the chemical cleaning in KOH + H₂O₂. The proposed cleaning procedures might be generally applied to various kinds of Au electrodes fabricated with the same conditions comparable with those are introduced in this study.

Brain Wave-Like Signal Modulator by Ionic Nanochannel Rectifier Bridges

Smart modulation of bioelectric signals is of great significance for the development of brain-computer interfaces, bio-computers, and other technologies. The regulation and transmission of bioelectrical signals are realized through the synergistic action of various ion channels in organisms. The bionic nanochannels, which have similar physiological working environment and ion rectification as their biological counterparts, can be used to construct ion rectifier bridges to modulate the bioelectric signals. Here, the artificial smart ionic rectifier bridge with light response is constructed by anodic aluminum oxide (AAO)/poly (spiropyran acrylate) (PSP) nanochannels. The output ion current of the rectifier bridge can be switched between "ON" and "OFF" states by irradiation with UV and visible (Vis) light, and the conversion efficiency (η) of the system in "ON" state is ≈70.5%. The controllable modulation of brain wave-like signal can be realized by ionic rectifier bridge. The ion transport properties and processes of ion rectifier bridges are explained using theoretical calculations based on Poisson-Nernst-Planck (PNP) equations. These findings have significant implications for the understanding of the intelligent ionic circuit and combination of artificial smart ionic channels to organisms, which provide new avenues for development of intelligent ion devices.

Development of GO/Co/Chitosan-Based Nano-Biosensor for Real-Time Detection of D-Glucose

Electrochemical nano-biosensor systems are popular in the industrial field, along with evaluations of medical, agricultural, environmental and sports analysis, because they can simultaneously perform qualitative and quantitative analyses with high sensitivity. However, real-time detection using an electrochemical nano-biosensor is greatly affected by the surrounding environment with the performance of the electron transport materials. Therefore, many researchers are trying to find good factors for real-time detection. In this work, it was found that a composite composed of graphite oxide/cobalt/chitosan had strong stability and electron transfer capability and was applied to a bioelectrochemical nano-biosensor with high sensitivity and stability. As a mediator-modified electrode, the GO/Co/chitosan composite was electrically deposited onto an Au film electrode by covalent boding, while glucose oxidase as a receptor was immobilized on the end of the GO/Co/chitosan composite. It was confirmed that the electron transfer ability of the GO/Co/chitosan composite was excellent, as shown with power density analysis. In addition, the real-time detection of D-glucose could be successfully performed by the developed nano-biosensor with a high range of detected concentrations from 1.0 to 15.0 mM. Furthermore, the slope value composed of the current, per the concentration of D-glucose as a detection response, was significantly maintained even after 14 days.

Controlled, partially exfoliated, self-supported functionalized flexible graphitic carbon foil for ultrasensitive detection of SARS-CoV-2 spike protein

This paper reports on an ultrasensitive and label-free electrochemical immunosensor for monitoring the SARS-CoV-2 spike protein (SARS-CoV-2 SP). A self-supported electrode, which can simultaneously serve as an antibody immobilization matrix and electron transport channel, was initially fabricated by a controlled partial exfoliation of a flexible graphitic carbon foil (GCF). Mild acidic treatment enabled the partial oxidation and exfoliation (down to a few layers) of the flexible GCF; this also provided a high percentage of oxygen functionality and an enhanced surface roughness. The substrate electrode was further functionalized with ethylenediamine (EDA) to provide a suitable platform with even a higher surface roughness, for the covalent immobilization of an anti-SARS-CoV-2 antibody. The change in the current response for the [Fe(CN)6]3-/4- redox couple, induced by the binding of SARS-CoV-2 SP to the antibody immobilized on the electrode surface, was used to determine the SARS-CoV-2 SP concentration. The immunosensor thus prepared could detect SARS-CoV-2 SP within 30 min with high reproducibility and specificity over a wide concentration range (0.2-100 ng/mL). Detection limits of 25 pg/mL and 27 pg/mL were found in a phosphate buffer solution (pH 7.4), and diluted blood plasma, respectively. The immunosensor was also employed to detect SARS-CoV-2 SP in artificial human saliva.

Methodological Approaches for Monitoring Five Major Food Safety Hazards Affecting Food Production in the Galicia-Northern Portugal Euroregion

The agri-food industry has historically determined the socioeconomic characteristics of Galicia and Northern Portugal, and it was recently identified as an area for collaboration in the Euroregion. In particular, there is a need for action to help to ensure the provision of safe and healthy foods by taking advantage of key enabling technologies. The goals of the FOODSENS project are aligned with this major objective, specifically with the development of biosensors able to monitor hazards relevant to the safety of food produced in the Euroregion. The present review addresses the state of the art of analytical methodologies and techniques-whether commercially available or in various stages of development-for monitoring food hazards, such as harmful algal blooms, mycotoxins, Listeria monocytogenes, allergens, and polycyclic aromatic hydrocarbons. We discuss the pros and cons of these methodologies and techniques and address lines of research for point-of-care detection. Accordingly, the development of miniaturized automated monitoring strategies is considered a priority in terms of health and economic interest, with a significant impact in several areas, such as food safety, water quality, pollution control, and public health. Finally, we present potential market opportunities that could result from the availability of rapid and reliable commercial methodologies.

Carbon Materials in Electroanalysis of Preservatives: A Review

Electrochemical sensors in electroanalysis are a particularly useful and relatively simple way to identify electroactive substances. Among the materials used to design sensors, there is a growing interest in different types of carbon. This is mainly due to its non-toxic properties, low cost, good electrical conductivity, wide potential range, and the possibility of using it in both aqueous and nonaqueous media. The electrodes made of carbon, and especially of carbon modified with different materials, are currently most often used in the voltammetric analysis of various compounds, including preservatives. The objective of this paper is to present the characteristics and suitability of different carbon materials for the construction of working electrodes used in the voltammetric analysis. Various carbon materials were considered and briefly discussed. Their analytical application was presented on the example of the preservatives commonly used in food, cosmetic, and pharmaceutical preparations. It was shown that for the electroanalysis of preservatives, mainly carbon electrodes modified with various modifiers are used. These modifications ensure appropriate selectivity, high sensitivity, low limits of detection and quantification, as well as a wide linearity range of voltammetric methods of their identification and determination.

A Dual Approach of an Oil-Membrane Composite and Boron-Doped Diamond Electrode to Mitigate Biofluid Interferences

Electrochemical biosensors promise a simple method to measure analytes for both point-of-care diagnostics and continuous, wearable biomarker monitors. In a liquid environment, detecting the analyte of interest must compete with other solutes that impact the background current, such as redox-active molecules, conductivity changes in the biofluid, water electrolysis, and electrode fouling. Multiple methods exist to overcome a few of these challenges, but not a comprehensive solution. Presented here is a combined boron-doped diamond electrode and oil–membrane protection approach that broadly mitigates the impact of biofluid interferents without a biorecognition element. The oil–membrane blocks the majority of interferents in biofluids that are hydrophilic while permitting passage of important hydrophobic analytes such as hormones and drugs. The boron-doped diamond then suppresses water electrolysis current and maintains peak electrochemical performance due to the foulant-mitigation benefits of the oil–membrane protection. Results show up to a 365-fold reduction in detection limits using the boron-doped diamond electrode material alone compared with traditional gold in the buffer. Combining the boron-doped diamond material with the oil–membrane protection scheme maintained these detection limits while exposed to human serum for 18 h.

Recent Advances in Enzymatic and Non-Enzymatic Electrochemical Glucose Sensing

The detection of glucose is crucial in the management of diabetes and other medical conditions but also crucial in a wide range of industries such as food and beverages. The development of glucose sensors in the past century has allowed diabetic patients to effectively manage their disease and has saved lives. First-generation glucose sensors have considerable limitations in sensitivity and selectivity which has spurred the development of more advanced approaches for both the medical and industrial sectors. The wide range of application areas has resulted in a range of materials and fabrication techniques to produce novel glucose sensors that have higher sensitivity and selectivity, lower cost, and are simpler to use. A major focus has been on the development of enzymatic electrochemical sensors, typically using glucose oxidase. However, non-enzymatic approaches using direct electrochemistry of glucose on noble metals are now a viable approach in glucose biosensor design. This review discusses the mechanisms of electrochemical glucose sensing with a focus on the different generations of enzymatic-based sensors, their recent advances, and provides an overview of the next generation of non-enzymatic sensors. Advancements in manufacturing techniques and materials are key in propelling the field of glucose sensing, however, significant limitations remain which are highlighted in this review and requires addressing to obtain a more stable, sensitive, selective, cost efficient, and real-time glucose sensor.

Analytical Parameters of a Novel Glucose Biosensor Based on Grafted PFM as a Covalent Immobilization Technique

Bioanalytical methods, in particular electrochemical biosensors, are increasingly used in different industrial sectors due to their simplicity, low cost, and fast response. However, to be able to reliably use this type of device, it is necessary to undertake in-depth evaluation of their fundamental analytical parameters. In this work, analytical parameters of an amperometric biosensor based on covalent immobilization of glucose oxidase (GOx) were evaluated. GOx was immobilized using plasma-grafted pentafluorophenyl methacrylate (pgPFM) as an anchor onto a tailored HEMA-co-EGDA hydrogel that coats a titanium dioxide nanotubes array (TiO2NTAs). Finally, chitosan was used to protect the enzyme molecules. The biosensor offered outstanding analytical parameters: repeatability (RSD = 1.7%), reproducibility (RSD = 1.3%), accuracy (deviation = 4.8%), and robustness (RSD = 2.4%). In addition, the Ti/TiO2NTAs/ppHEMA-co-EGDA/pgPFM/GOx/Chitosan biosensor showed good long-term stability; after 20 days, it retained 89% of its initial sensitivity. Finally, glucose concentrations of different food samples were measured and compared using an official standard method (HPLC). Deviation was lower than 10% in all measured samples. Therefore, the developed biosensor can be considered to be a reliable analytical tool for quantification measurements.

Chitosan-based enzyme ink for screen-printed bioanodes

In this study, magnesium oxide (MgO)-templated mesoporous carbon (MgOC) and chitosan cross-linked with genipin (chitosan-genipin) were considered bio-composite inks for screen-printed bioanodes. The fabrication processes were optimized using rheological and structural data, and a bioanode ink containing glucose oxidase (GOx) and 1,2-naphthoquinone (1,2-NQ) was successfully developed. The optimal bioanode-ink contained MgOC pre-treated by washing to achieve a hydrophilic and neutral surface, which helped maintain enzyme activity and resulted in a highly porous electrode structure, which is essential for the accessibility of glucose to GOx. A bioanode fabricated using this ink showed a linear response current dependency up to 8 mM glucose with a sensitivity of 25.83 μA cm-2 mM-1. Combined with a conventional biocathode, an electromotive force of 0.54 V and a maximal power density of 96 μW cm-2 were achieved. These results show that this bio-composite ink can be used to replace the multi-step process of printing with conventional ink followed by drop-casting enzyme and mediator with a one-step printing process.

Reduced Graphene Oxide and Polyaniline Nanofibers Nanocomposite for the Development of an Amperometric Glucose Biosensor

The control of glucose concentration is a crucial factor in clinical diagnosis and the food industry. Electrochemical biosensors based on reduced graphene oxide (rGO) and conducting polymers have a high potential for practical application. A novel thermal reduction protocol of graphene oxide (GO) in the presence of malonic acid was applied for the synthesis of rGO. The rGO was characterized by scanning electron microscopy, X-ray diffraction analysis, Fourier-transform infrared spectroscopy, and Raman spectroscopy. rGO in combination with polyaniline (PANI), Nafion, and glucose oxidase (GOx) was used to develop an amperometric glucose biosensor. A graphite rod (GR) electrode premodified with a dispersion of PANI nanostructures and rGO, Nafion, and GOx was proposed as the working electrode of the biosensor. The optimal ratio of PANI and rGO in the dispersion used as a matrix for GOx immobilization was equal to 1:10. The developed glucose biosensor was characterized by a wide linear range (from 0.5 to 50 mM), low limit of detection (0.089 mM), good selectivity, reproducibility, and stability. Therefore, the developed biosensor is suitable for glucose determination in human serum. The PANI nanostructure and rGO dispersion is a promising material for the construction of electrochemical glucose biosensors.

Electrochemical biosensors: a nexus for precision medicine

Precision medicine is a field with huge potential for improving a patient's quality of life, wherein therapeutic drug monitoring (TDM) can provide actionable insights. More importantly, incorrect drug dose is a common contributor to medical errors. However, current TDM practice is time-consuming and expensive, and requires specialised technicians. One solution is to use electrochemical biosensors (ECBs), which are inexpensive, portable, and highly sensitive. In this review, we explore the potential for ECBs as a technology for on-demand drug monitoring, including microneedles, continuous monitoring, synthetic biorecognition elements, and multi-material electrodes. We also highlight emerging strategies to achieve continuous drug monitoring, and conclude by appraising recent developments and providing an outlook for the field.