Polyaromatic Hydrocarbon-Functionalized 2D MXene-Based 3D Porous Antifouling Nanocomposite with Long Shelf Life for High-Performance Electrochemical Immunosensor Applications

Affinity-based electrochemical (AEC) biosensors have gained more attention in the field of point-of-care management. However, AEC sensing is hampered by biofouling of the electrode surface and degradation of the antifouling material. Therefore, a breakthrough in antifouling nanomaterials is crucial for the fabrication of reliable AEC biosensors. Herein, for the first time, we propose 1-pyrenebutyric acid-functionalized MXene to develop an antifouling nanocomposite to resist biofouling in the immunosensors. The nanocomposite consisted of a 3D porous network of bovine serum albumin cross-linked with glutaraldehyde with functionalized MXene as conductive nanofillers, where the inherited oxidation resistance property of functionalized MXene improved the electrochemical lifetime of the nanocomposite. On the other hand, the size-extruded porous structure of the nanocomposite inhibited the biofouling activity on the electrode surface for up to 90 days in real samples. As a proof of concept, the antifouling nanocomposite was utilized to fabricate a multiplexed immunosensor for the detection of C-reactive protein (CRP) and ferritin biomarkers. The fabricated sensor showed good selectivity over time and an excellent limit of detection for CRP and ferritin of 6.2 and 4.2 pg/mL, respectively. This research successfully demonstrated that functionalized MXene-based antifouling nanocomposites have great potential to develop high-performance and low-cost immunosensors.

Stochastic Electrochemical Measurement of a Biofouling Layer on Gold

Adsorption of a biofouling layer on the surface of biosensors decreases the electrochemical activity and hence shortens the service life of biosensors, particularly implantable and wearable biosensors. Real-time quantification of the loss of activity is important for in situ assessment of performance while presenting an opportunity to compensate for the loss of activity and recalibrate the sensor to extend the service life. Here, we introduce an electrochemical noise measurement technique as a tool for the quantification of the formation of a biofouling layer on the surface of gold. The technique uniquely affords thermodynamic and kinetic information without applying an external bias (potential and/or current), hence allowing the system to be appraised in its innate state. The technique relies on the analysis of non-faradaic current and potential fluctuations that are intrinsically generated by the interaction of charged species at the electrode surface, i.e., gold. An analytical model is extended to explain the significance of parameters drawn from statistical analysis of the noise signal. This concept is then examined in buffered media in the presence of albumin, a common protein in the blood and a known source of a fouling layer in biological systems. Results indicate that the statistical analysis of the noise signal can quantify the loss of electrochemical activity, which is also corroborated by impedance spectroscopy as a complementary technique.

Recent advances in enzymatic biofuel cells enabled by innovative materials and techniques

The past few decades have seen increasingly rapid advances in the field of sustainable energy technologies. As a new bio- and eco-friendly energy source, enzymatic biofuel cells (EBFCs) have garnered significant research interest due to their capacity to power implantable bioelectronics, portable devices, and biosensors by utilizing biomass as fuel under mild circumstances. Nonetheless, numerous obstacles impeded the commercialization of EBFCs, including their relatively modest power output and poor long-term stability of enzymes. To depict the current progress of EBFC and address the challenges it faces, this review traces back the evolution of EBFC and focuses on contemporary advances such as newly emerged multi or single enzyme systems, various porous framework-enzyme composites techniques, and innovative applications. Besides emphasizing current achievements in this field, from our perspective part we also introduced novel electrode and cell design for highly effective EBFC fabrication. We believe this review will assist readers in comprehending the basic research and applications of EBFCs as well as potentially spark interdisciplinary collaboration for addressing the pressing issues in this field.

Perspectives and trends in advanced optical and electrochemical biosensors based on engineered peptides

With the advancement of life medicine, in vitro diagnostics (IVD) technology has become an auxiliary tool for early diagnosis of diseases. However, biosensors for IVD now face some disadvantages such as poor targeting, significant antifouling properties, low density of recognized molecules, and poor stability. In recent years, peptides have been demonstrated to have various functions in unnatural biological systems, such as targeting properties, antifouling properties, and self-assembly properties, which indicates that peptides can be engineered. These properties of peptides, combined with their good biocompatibility, can be well applied to the design of biosensors to solve the problems mentioned above. This review provides an overview of the properties of engineered functional peptides and their applications in enhancing biosensor performance, mainly in the field of optics and electrochemistry.

pH-Activated Dissolvable Polymeric Coatings to Reduce Biofouling on Electrochemical Sensors

Implantable electrochemical sensors that enable the real-time detection of significant biomarkers offer huge potential for the enhancement and personalisation of therapies; however, biofouling is a key challenge encountered by any implantable system. This is particularly an issue immediately after implantation, when the foreign body response and associated biofouling processes are at their most active in passivating a foreign object. Here, we present the development of a sensor protection and activation strategy against biofouling, based on coatings consisting of a pH-triggered, dissolvable polymer, that covered a functionalised electrode surface. We demonstrate that reproducible delayed sensor activation can be achieved, and that the length of this delay can be controlled by the optimisation of coating thickness, homogeneity and density through tuning of the coating method and temperature. Comparative evaluation of the polymer-coated and uncoated probe-modified electrodes in biological media revealed significant improvements in their anti-biofouling characteristics, demonstrating that this offers a promising approach to the design of enhanced sensing devices.

Functional Nanomaterials Enhancing Electrochemical Biosensors as Smart Tools for Detecting Infectious Viral Diseases

Electrochemical biosensors are known as analytical tools, guaranteeing rapid and on-site results in medical diagnostics, food safety, environmental protection, and life sciences research. Current research focuses on developing sensors for specific targets and addresses challenges to be solved before their commercialization. These challenges typically include the lowering of the limit of detection, the widening of the linear concentration range, the analysis of real samples in a real environment and the comparison with a standard validation method. Nowadays, functional nanomaterials are designed and applied in electrochemical biosensing to support all these challenges. This review will address the integration of functional nanomaterials in the development of electrochemical biosensors for the rapid diagnosis of viral infections, such as COVID-19, middle east respiratory syndrome (MERS), influenza, hepatitis, human immunodeficiency virus (HIV), and dengue, among others. The role and relevance of the nanomaterial, the type of biosensor, and the electrochemical technique adopted will be discussed. Finally, the critical issues in applying laboratory research to the analysis of real samples, future perspectives, and commercialization aspects of electrochemical biosensors for virus detection will be analyzed.

Insight into continuous glucose monitoring: from medical basics to commercialized devices

According to the latest statistics, more than 537 million people around the world struggle with diabetes and its adverse consequences. As well as acute risks of hypo- or hyper- glycemia, long-term vascular complications may occur, including coronary heart disease or stroke, as well as diabetic nephropathy leading to end-stage disease, neuropathy or retinopathy. Therefore, there is an urgent need to improve diabetes management to reduce the risk of complications but also to improve patient's quality life. The impact of continuous glucose monitoring (CGM) is well recognized, in this regard. The current review aims at introducing the basic principles of glucose sensing, including electrochemical and optical detection, summarizing CGM technology, its requirements, advantages, and disadvantages. The role of CGM systems in the clinical diagnostics/personal testing, difficulties in their utilization, and recommendations are also discussed. In the end, challenges and prospects in future CGM systems are discussed and non-invasive, wearable glucose biosensors are introduced. Though the scope of this review is CGMs and provides information about medical issues and analytical principles, consideration of broader use will be critical in future if the right systems are to be selected for effective diabetes management.

Functional Fiber Materials to Smart Fiber Devices

The development of fiber materials has accompanied the evolution of human civilization for centuries. Recent advances in materials science and chemistry offered fibers new applications with various functions, including energy harvesting, energy storing, displaying, health monitoring and treating, and computing. The unique one-dimensional shape of fiber devices endows them advantages to work as human-interfaced electronics due to the small size, lightweight, flexibility, and feasibility for integration into large-scale textile systems. In this review, we first present a discussion of the basics of fiber materials and the design principles of fiber devices, followed by a comprehensive analysis on recently developed fiber devices. Finally, we provide the current challenges facing this field and give an outlook on future research directions. With novel fiber devices and new applications continuing to be discovered after two decades of research, we envision that new fiber devices could have an important impact on our life in the near future.

Tethering zwitterionic polymer coatings to mediated glucose biosensor enzyme electrodes can decrease sensor foreign body response yet retain sensor sensitivity to glucose

Foreign body response (FBR) is a major challenge that affects implantable biosensors and medical devices, including glucose biosensors, leading to a deterioration in device response over time. Polymer shields are often used to mitigate this issue. Zwitterionic polymers (ZPs) are a promising class of materials that reduce biofouling of implanted devices. A series of ZPs each containing tetherable epoxide functional groups was synthesised for application as a polymer shield for eventual application as implantable glucose biosensors. The polymer shields were initially tested for the ability to resist fibrinogen adsorption and fibroblast adhesion. All synthesised ZPs showed comparable behaviour to a commercial Lipidure ZP in resisting fibrinogen adsorption. Nafion, a common anionic shield used against electrochemical interferents, showed higher protein adsorption and comparable cell adhesion resistance as uncoated control surfaces. However, a poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate) (MPC)-type ZP showed similar behaviour to Lipidure, with approximately 50% reduced fibrinogen adsorption and 80% decrease in fibroblast adhesion compared to uncoated controls. An MPC-coated amperometric glucose biosensor showed comparable current density and a 1.5-fold increase in sensitivity over an uncoated control biosensor, whereas all other polymer shields tested, including Lipidure, Nafion and a poly(ethyleneglycol) polymer, resulted in lower sensitivity and current density. Collectively, these characteristics make MPC-polymer shield coatings an appealing possibility for use in implantable glucose sensors and other implanted devices with the aim of reducing FBR while maintaining sensor performance.

Printed Antifouling Electrodes for Biosensing Applications

Biosensors based on miniaturized, functional electrodes are of high potential for various biosensing applications, especially at the point-of-care setting among others. However, the sensor performance of such electrochemical devices is still strongly limited, especially due to surface fouling in complex sample fluids, such as blood serum. Electrode coatings based on conductive nanomaterials embedded in antifouling matrices offer a promising strategy to overcome this limitation. However, known composite coatings require long (typically >24 h) and complex fabrication processes, which pose a strong barrier for cost-effective mass manufacturing and successful commercialization. Here, we describe a novel polymer/carbon nanotube (CNT) composite coating that can be produced from an ink containing a photoreactive and antifouling copolymer as well as conductive CNTs using fast and highly scalable printing processes. Coatings were prepared on screen-printed electrodes and characterized using cyclic voltammetry (CV) and protein fouling experiments. The coatings offered an electroactive surface area (EASA) comparable to uncoated screen-printed electrodes and retained >90% of initial EASA after 1 h of exposure to concentrated bovine serum albumin solution, while uncoated electrodes decreased to <20% of initial EASA after the same treatment. Utilizing the universal crosslinking reaction of the polymer coating, antibodies against the inflammatory biomarker C-reactive protein (CRP) were photochemically immobilized on the electrodes. Functionalized electrodes were fabricated in <2 h and were successfully used to quantify nanogram-range concentrations of CRP spiked in undiluted human blood serum using a sandwich-immunoassay with electrochemical read-out, demonstrating the high potential of the platform for biosensing applications.

Catalytic Biosensors Operating under Quasi-Equilibrium Conditions for Mitigating the Changes in Substrate Diffusion

Despite the success of continuous glucose measuring systems operating through the skin for about 14 days, long-term implantable biosensors are facing challenges caused by the foreign-body reaction. We present a conceptually new strategy using catalytic enzyme-based biosensors based on a measuring sequence leading to minimum disturbance of the substrate equilibrium concentration by controlling the sensor between "on" and "off" state combined with short potentiometric data acquisition. It is required that the enzyme activity can be completely switched off and no parasitic side reactions allow substrate turnover. This is achieved by using an O₂ -independent FAD-dependent glucose dehydrogenase embedded within a crosslinked redox polymer. A short measuring interval allows the glucose concentration equilibrium to be restored quickly which enables the biosensor to operate under quasi-equilibrium conditions.

Rapid Point-of-Care Electrochemical Sensor for the Detection of Cancer Tn Antigen Carbohydrate in Whole Unprocessed Blood

Improving outcomes for cancer patients during treatment and monitoring for cancer recurrence requires personalized care which can only be achieved through regular surveillance for biomarkers. Unfortunately, routine detection for blood-based biomarkers is cost-prohibitive using currently specialized laboratories. Using a rapid self-assembly sensing interface amenable to methods of mass production, we demonstrate the ability to detect and quantify a small carbohydrate-based cancer biomarker, Tn antigen (αGalNAc-Ser/Thr) in a small volume of blood, using a test format strip reminiscent of a blood glucose test. The detection of Tn antigen at picomolar levels is achieved through a new transduction mechanism based on the impact of Tn antigen interactions on the molecular dynamic motion of a lectin cross-linked lubricin antifouling brush. In tests performed on retrospective blood plasma samples from patients presenting three different tumor types, differentiation between healthy and diseased patients was achieved, highlighting the clinical potential for cancer monitoring.

Angiotensin-Converting Enzyme 2-Based Biosensing Modalities and Devices for Coronavirus Detection

Rapid and cost-effective diagnostic tests for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are a critical and valuable weapon for the coronavirus disease 2019 (COVID-19) pandemic response. SARS-CoV-2 invasion is primarily mediated by human angiotensin-converting enzyme 2 (hACE2). Recent developments in ACE2-based SARS-CoV-2 detection modalities accentuate the potential of this natural host-virus interaction for developing point-of-care (POC) COVID-19 diagnostic systems. Although research on harnessing ACE2 for SARS-CoV-2 detection is in its infancy, some interesting biosensing devices have been developed, showing the commercial viability of this intriguing new approach. The exquisite performance of the reported ACE2-based COVID-19 biosensors provides opportunities for researchers to develop rapid detection tools suitable for virus detection at points of entry, workplaces, or congregate scenarios in order to effectively implement pandemic control and management plans. However, to be considered as an emerging approach, the rationale for ACE2-based biosensing needs to be critically and comprehensively surveyed and discussed. Herein, we review the recent status of ACE2-based detection methods, the signal transduction principles in ACE2 biosensors and the development trend in the future. We discuss the challenges to development of ACE2-biosensors and delineate prospects for their use, along with recommended solutions and suggestions.

Combinatorial Polyacrylamide Hydrogels for Preventing Biofouling on Implantable Biosensors

Biofouling on the surface of implanted medical devices and biosensors severely hinders device functionality and drastically shortens device lifetime. Poly(ethylene glycol) and zwitterionic polymers are currently considered "gold-standard" device coatings to reduce biofouling. To discover novel anti-biofouling materials, a combinatorial library of polyacrylamide-based copolymer hydrogels is created, and their ability is screened to prevent fouling from serum and platelet-rich plasma in a high-throughput parallel assay. It is found that certain nonintuitive copolymer compositions exhibit superior anti-biofouling properties over current gold-standard materials, and machine learning is used to identify key molecular features underpinning their performance. For validation, the surfaces of electrochemical biosensors are coated with hydrogels and their anti-biofouling performance in vitro and in vivo in rodent models is evaluated. The copolymer hydrogels preserve device function and enable continuous measurements of a small-molecule drug in vivo better than gold-standard coatings. The novel methodology described enables the discovery of anti-biofouling materials that can extend the lifetime of real-time in vivo sensing devices.

Combinatorial Polyacrylamide Hydrogels for Preventing Biofouling on Implantable Biosensors

Biofouling on the surface of implanted medical devices and biosensors severely hinders device functionality and drastically shortens device lifetime. Poly(ethylene glycol) and zwitterionic polymers are currently considered "gold-standard" device coatings to reduce biofouling. To discover novel anti-biofouling materials, a combinatorial library of polyacrylamide-based copolymer hydrogels is created, and their ability is screened to prevent fouling from serum and platelet-rich plasma in a high-throughput parallel assay. It is found that certain nonintuitive copolymer compositions exhibit superior anti-biofouling properties over current gold-standard materials, and machine learning is used to identify key molecular features underpinning their performance. For validation, the surfaces of electrochemical biosensors are coated with hydrogels and their anti-biofouling performance in vitro and in vivo in rodent models is evaluated. The copolymer hydrogels preserve device function and enable continuous measurements of a small-molecule drug in vivo better than gold-standard coatings. The novel methodology described enables the discovery of anti-biofouling materials that can extend the lifetime of real-time in vivo sensing devices.

Plastic-based lateral flow immunoassay device for electrochemical detection of NT-proBNP

Here we report an easily fabricated, plastic-based lateral flow device for carrying out metalloimmunoassays. The device is called ocFlow to emphasize the open-channel design. We have shown that the ocFlow is capable of magnetic microbead (MμB)-based metalloimmunoassays for the detection of two types of immunoconjugates: a model composite (MC) and a sandwich immunoassay for the heart failure marker NT-proBNP. In both assays, Ag nanoparticles (AgNPs) were used as electrochemically detectable labels. NT-proBNP and MC concentrations as low as 750.0 pM and 10.0 pM, respectively, could be detected using the ocFlow device. Four key conclusions can be drawn from the results presented herein. First, immunoconjugates attached to the MμBs can be transported in the flow channel using combined hydrodynamic and capillary pressure passive pumping. Second, the ocFlow device is capable of on-chip storage, resolvation, and conjugate formation of both the MC and NT-proBNP composites. Third, electrochemical detection can be conducted on analytes suspended in serum by rinsing the electrodes with a wash buffer. Finally, and perhaps most significantly, the assay is quantitative and has a detection limit for NT-proBNP in the high picomolar range when the necessary reagents are stored on the device in a dry form.

Recombinant Histidine-Tagged Nano-protein-based Highly Sensitive Electro-Sensing Device for Salivary Cortisol

We have developed a powerful biosensing strategy for immobilizing histidine-tagged (His-Tag)-oriented recombinant nano-protein immobilization on a chemically modified glassy carbon electrode (GCE) surfaces via (S)-N-(5-amino-1-carboxypentyl)iminodiacetic acid (ANTA) acting as a chelating Ni2+ centered interaction. Here, we introduce a label-free electro-sensor to quantify cortisol levels in saliva samples for point-of-care testing (POCT). The high specificity of the chemically modified GCE was established by genetically bio-engineered metal-binding sites on the selected recombinant apoferritin (R-AFTN) nano-protein to impart functionality to its surface and by coating the carbon surface with the self-assembled monolayers of 4-aminobenzoic acid (4-ABA) attached to ANTA groups complexed with Ni2+ transition metal ions. Despite the variety of conventional assays available to monitor cortisol levels, they require bulky exterior outfits, which hinders use in the healthcare systems. Therefore, we performed a rapid, easy-to-implement, and low-cost quantitative electro-sensor to enable the real-time detection of cortisol levels in saliva samples. As a result, the cortisol electro-sensor fabricated with high specificity utilizing a GCE could measure cortisol levels with a detection limit of 0.95 ng/ml and sensitivity of 7.91 μA/(ng/mL), which is a practical approach in human saliva. Thus, protein nanoprobe-based cortisol biosensing showed high sensitivity and selectivity for the direct electro-sensing of cortisol for POCT.

Rational design of smart nano-platforms based on antifouling-nanomaterials toward multifunctional bioanalysis

The ability to design nanoprobe devices with the capability of quantitative/qualitative operation in complex media will probably underpin the main upcoming progress in healthcare research and development. However, the biomolecules abundances in real samples can considerably alter the interface performance, where unwanted adsorption/adhesion can block signal response and significantly decrease the specificity of the assay. Herein, this review firstly offers a brief outline of several significances of fabricating high-sensitivity and low-background interfaces to adjust various targets' behaviors induced via bioactive molecules on the surface. Besides, some important strategies to resist non-specific protein adsorption and cell adhesion, followed by imperative categories of antifouling reagents utilized in the construction of high-performance solid sensory interfaces, are discussed. The next section specifically highlights the various nanocomposite probes based on antifouling-nanomaterials for electrode modification containing carbon nanomaterials, noble metal nanoparticles, magnetic nanoparticles, polymer, and silicon-based materials in terms of nanoparticles, rods, or porous materials through optical or chemical strategies. We specially outline those nanoprobes that are capable of identification in complex media or those using new constructions/methods. Finally, the necessity and requirements for future advances in this emerging field are also presented, followed by opportunities and challenges.

A Micro Electrochemical Sensor for Multi-Analyte Detection Based on Oxygenated Graphene Modified Screen-Printed Electrode

Electrode interfaces with both antibiofouling properties and electrocatalytic activity can promote the practical application of nonenzymatic electrochemical sensors in biological fluids. Compared with graphene, graphene oxide (GO) possesses unique properties such as superior solubility (hydrophilicity) in water, negative charge, and abundant oxygenated groups (oxo functionalities) in the plane and edge sites, which play an essential role in electrocatalysis and functionalization. In this work, a micro electrochemical sensor consisting of GO-modified screen-printed electrode and PDMS micro-cell was designed to achieve multi-analyte detection with excellent selectivity and anti-biofouling properties by electrochemically tuning the oxygen-containing functional species, hydrophilicity/hydrophobicity, and electrical conductivity. In particular, the presented electrodes demonstrated the potential in the analysis of biological samples in which electrodes often suffer from serious biofouling. The interaction of proteins with electrodes as well as uric acid was investigated and discussed.

Densification of Diazonium-Based Organic Thin Film as Bioelectrical Interface

Aryl diazonium chemistry generates a covalently attached thin film on various materials. This chemistry has diverse applications owing to the stability, ease of functionalization, and versatility of the film. However, the uncontrolled growth into a polyaryl film has limited the controllability of the film's beneficial properties. In this study, we developed a multistep grafting protocol to densify the film while maintaining a thickness on the order of nanometers. This simple protocol enabled the full passivation of a nitrophenyl polyaryl film, completely eliminating the electrochemical reactions at the surface. We then applied this protocol to the grafting of phenylphosphorylcholine films, with which the densification significantly enhanced the antifouling property of the film. Together with its potential to precisely control the density of functionalized surfaces, we believe this grafting procedure will have applications in the development of bioelectrical interfaces.

Cortisol Detection in Undiluted Human Serum Using a Sensitive Electrochemical Structure-Switching Aptamer over an Antifouling Nanocomposite Layer

There is a strong and growing need to monitor stress biomarkers in vivo for real-time emotional and wellness assessment. Toward this, we report a reagent-free electrochemical aptasensor with a nanocomposite antifouling layer for sensitive and continuous detection of cortisol in human serum. A thiolated, methylene blue (MB)-tagged conformation-switching aptamer was immobilized over a gold nanowire (AuNW) nanocomposite to capture cortisol and generate a signal proportional to the cortisol concentration. The signal is recorded through differential pulse voltammetry (DPV) and chronoamperometry. The aptasensor exhibited a sensitive response with 0.51 and 0.68 nM detection limits in spiked buffer and undiluted serum samples, respectively. Interference from other structurally similar analogs, namely, epinephrine and cholic acid, was negligible (<10%). The developed nanocomposite-based aptasensor showed excellent stability in undiluted human serum, outperforming several other nanocomposite materials even after prolonged exposure. This work lays the foundation for new biosensor formats such as implantable and wearable sensors.

Recent Advances in Electrochemical Chitosan-Based Chemosensors and Biosensors: Applications in Food Safety

Chitosan is a biopolymer derived from chitin. It is a non-toxic, biocompatible, bioactive, and biodegradable polymer. Due to its properties, chitosan has found applications in several and different fields such as agriculture, food industry, medicine, paper fabrication, textile industry, and water treatment. In addition to these properties, chitosan has a good film-forming ability which allows it to be widely used for the development of sensors and biosensors. This review is focused on the use of chitosan for the formulation of electrochemical chemosensors. It also aims to provide an overview of the advantages of using chitosan as an immobilization platform for biomolecules by highlighting its applications in electrochemical biosensors. Finally, applications of chitosan-based electrochemical chemosensors and biosensors in food safety are illustrated.

Gold Nanoparticles/Carbon Nanotubes and Gold Nanoporous as Novel Electrochemical Platforms for L-Ascorbic Acid Detection: Comparative Performance and Application

Herein, the effects of nanostructured modifications of a gold electrode surface in the development of electrochemical sensors for L-ascorbic acid detection have been investigated. In particular, a bare gold electrode has been modified by electrodeposition of gold single-walled carbon nanotubes (Au/SWCNTs) and by the formation of a highly nanoporous gold (h-nPG) film. The procedure has been realized by sweeping the potential between +0.8 V and 0 V vs. Ag/AgCl for 25 scans in a suspension containing 5 mg/mL of SWCNTs in 10 mM HAuCl4 and 2.5 M NH4Cl solution for Au/SWCNTs modified gold electrode. A similar procedure was applied for a h-nPG electrode in a 10 mM HAuCl4 solution containing 2.5 M NH4Cl, followed by applying a fixed potential of −4 V vs. Ag/AgCl for 60 s. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the properties of the modified electrodes. The developed sensors showed strong electrocatalytic activity towards ascorbic acid oxidation with enhanced sensitivities of 1.7 × 10−2 μA μM−1cm−2 and 2.5 × 10−2 μA μM−1cm−2 for Au/SWCNTs and h-nPG modified electrode, respectively, compared to bare gold electrode (1.0 × 10−2 μA μM−1cm−2). The detection limits were estimated to be 3.1 and 1.8 μM, respectively. The h-nPG electrode was successfully used to determine ascorbic acid in human urine with no significant interference and with satisfactory recovery levels.

Integrating programmable DNAzymes with electrical readout for rapid and culture-free bacterial detection using a handheld platform

The detection and identification of bacteria currently rely on enrichment steps such as bacterial culture and nucleic acid amplification to increase the concentration of target analytes. These steps increase assay time, cost and complexity, making it difficult to realize a truly rapid point-of-care test. Here we report the development of an electrical assay that uses electroactive RNA-cleaving DNAzymes (e-RCDs) to identify specific bacterial targets and subsequently release a DNA barcode for transducing a signal onto an electrical chip. Integrating e-RCDs into a two-channel electrical chip with nanostructured electrodes provides the analytical sensitivity and specificity needed for clinical analysis. The e-RCD assay is capable of detecting 10 CFU (equivalent to 1,000 CFU ml^-1) of Escherichia coli selectively from a panel containing multiple non-specific bacterial species. Clinical evaluation of this assay using 41 patient urine samples demonstrated a diagnostic sensitivity of 100% and specificity of 78% at an analysis time of less than one hour compared with the several hours needed for currently used culture-based methods.

Electrochemical Biosensors in Food Safety: Challenges and Perspectives

Safety and quality are key issues for the food industry. Consequently, there is growing demand to preserve the food chain and products against substances toxic, harmful to human health, such as contaminants, allergens, toxins, or pathogens. For this reason, it is mandatory to develop highly sensitive, reliable, rapid, and cost-effective sensing systems/devices, such as electrochemical sensors/biosensors. Generally, conventional techniques are limited by long analyses, expensive and complex procedures, and skilled personnel. Therefore, developing performant electrochemical biosensors can significantly support the screening of food chains and products. Here, we report some of the recent developments in this area and analyze the contributions produced by electrochemical biosensors in food screening and their challenges.

An electrochemical aptasensor based on AuPt alloy nanoparticles for ultrasensitive detection of amyloid-β oligomers

Amyloid-β oligomer is an important biomarker and a potential therapeutic target of Alzheimer's disease in its early stage. Here, we combined superhydrophobic carbon fiber paper (CFP) with AuPt alloy nanoparticles to prepare a CFP/AuPt nanocomposite with larger specific surface area and hydrophobic surface. On this basis, we constructed an electrochemical aptasensor based on CFP/AuPt for the ultrasensitive detection of amyloid-β oligomers. The surface-coated AuPt nanoparticles greatly enhanced the electroactive area, and the hydrophobic surface increased the resisting nonspecific adsorption performance of sensor. A combination of these two features significantly improved the sensitivity and specificity of the sensor. This electrochemical aptasensor based on CFP/AuPt displayed a low detection limit of 0.16 pg/mL. This work shows a promising future in clinical diagnosis of Alzheimer's disease and provides a possible solution to electrochemical biosensors that are susceptible to interference in biological fluids.

Rapid and sensitive determination of doxorubicin in human whole blood by vertically-ordered mesoporous silica film modified electrochemically pretreated glassy carbon electrodes

Direct and accurate detection of doxorubicin (DOX) in unprocessed human whole blood is of vital importance in medical diagnosis and monitoring. In this work, we demonstrate the utilization of electrochemically pretreated glassy carbon electrodes (p-GCE) modified with vertically-ordered mesoporous silica films (VMSF) for rapid and sensitive electrochemical detection of DOX. The electrochemically pretreated process is a simple, cost-effective and environmentally friendly approach for improving interface catalytic properties and introducing oxygen-containing groups into the GCE surface, which could be suitable for stably growing VMSF without any adhesive layer simultaneously retaining the underlying electrode activity. Benefiting from the highly sensitive electrode substrate of p-GCE and electrostatic preconcentration effect of VMSF, the present VMSF/p-GCE sensor was able to determine DOX with an ultrahigh sensitivity (23.94 μA μM^-1) and a relatively low limit of detection (0.2 nM) and a rather wide linear range (0.5 nM to 23 μM). Furthermore, direct and reliable electrochemical detection of DOX in human whole blood without complicated sample pretreatments was achieved owing to the excellent anti-fouling and anti-interference ability of VMSF.

Multiplex Immunoassay Techniques for On-Site Detection of Security Sensitive Toxins

Biological toxins are a heterogeneous group of high molecular as well as low molecular weight toxins produced by living organisms. Due to their physical and logistical properties, biological toxins are very attractive to terrorists for use in acts of bioterrorism. Therefore, among the group of biological toxins, several are categorized as security relevant, e.g., botulinum neurotoxins, staphylococcal enterotoxins, abrin, ricin or saxitoxin. Additionally, several security sensitive toxins also play a major role in natural food poisoning outbreaks. For a prompt response to a potential bioterrorist attack using biological toxins, first responders need reliable, easy-to-use and highly sensitive methodologies for on-site detection of the causative agent. Therefore, the aim of this review is to present on-site immunoassay platforms for multiplex detection of biological toxins. Furthermore, we introduce several commercially available detection technologies specialized for mobile or on-site identification of security sensitive toxins.

Fluorescent Noble Metal Nanoclusters Loaded Protein Hydrogel Exhibiting Anti-Biofouling and Self-Healing Properties for Electrochemiluminescence Biosensing Applications

Electrochemiluminescence (ECL) showed great potential in various analytical applications, especially in the sensing of biotargets, taking advantage of its high sensitivity, selectivity, ease of spatial and temporal control, and simplified optical setup. However, during the sensing of complex biological samples, ECL sensors often suffered severe interferences from unavoidable nonspecific-binding of biomacromolecules and physical damages of ECL sensing interfaces. Herein, a hydrogel based ECL biosensing system exhibiting excellent anti-biofouling and self-healing properties is developed. A protein hydrogel composed of bovine serum albumin (BSA) directed fluorescent Au/Ag alloy nanoclusters (Au/Ag NCs) is applied in building ECL sensing systems. The hydrogel matrix facilitates the immobilization of fluorescent Au/Ag NCs as excellent ECL probes, and the porous hydrophilic structure allows the free diffusion of small molecular biotargets while rejecting macromolecular interferences. Moreover, the hydrogel exhibits excellent self-healing property, with the ECL intensity recovered rapidly in 10 min after cutting. The hydrogel ECL system is successfully applied in sensing glutathione (GSH) in serum, confirming the applicability of the hydrogel based anti-biofouling ECL sensing system in sensing complex biological samples. This research may inspire the development of novel anti-biofouling and self-healing ECL biosensors for biosensing applications.

Single particle detection of protein molecules using dark-field microscopy to avoid signals from nonspecific adsorption

A massively parallel single particle sensing method based on core-satellite formation of Au nanoparticles was introduced for the detection of interleukin 6 (IL-6). This method exploits the fact that the localized plasmon resonance (LSPR) of the plasmonic nanoparticles will change as a result of core-satellite formation, resulting in a change in the observed color. In this method, the hue (color) value of thousands of 67 nm Au nanoparticles immobilized on a glass coverslip surface is analyzed by a Matlab code before and after the addition of reporter nanoparticles containing IL-6 as target protein. The average hue shift as the result of core-satellite formation is used as the basis to detect small amount of proteins. This method enjoys two major advantages. First it is able to analyze the hue values of thousands of nanoparticles in parallel in less than a minute. Secondly the method is able to circumvent the effect of non-specific adsorption, a major issue in the field of biosensing.

Functional Molecular Interfaces for Impedance-Based Diagnostics

In seeking to develop and optimize reagentless electroanalytical assays, a consideration of the transducing interface features lies key to any subsequent sensitivity and selectivity. This review briefly summarizes some of the most commonly used receptive interfaces that have been employed within the development of impedimetric molecular sensors. We discuss the use of high surface area carbon, nanoparticles, and a range of bioreceptors that can subsequently be integrated. The review spans the most commonly utilized biorecognition elements, such as antibodies, antibody fragments, aptamers, and nucleic acids, and touches on some novel emerging alternatives such as nanofragments, molecularly imprinted polymers, and bacteriophages. Reference is made to the immobilization chemistries available along with a consideration of both optimal packing density and recognition probe orientation. We also discuss assay-relevant mechanistic details and applications in real sample analysis.

Application of Biosensors for Detection of Pathogenic Food Bacteria: A Review

The use of biosensors is considered a novel approach for the rapid detection of foodborne pathogens in food products. Biosensors, which can convert biological, chemical, or biochemical signals into measurable electrical signals, are systems containing a biological detection material combined with a chemical or physical transducer. The objective of this review was to present the effectiveness of various forms of sensing technologies for the detection of foodborne pathogens in food products, as well as the criteria for industrial use of this technology. In this article, the principle components and requirements for an ideal biosensor, types, and their applications in the food industry are summarized. This review also focuses in detail on the application of the most widely used biosensor types in food safety.

Patterned Molecular Films of Alkanethiol and PLL-PEG on Gold-Silicate Interfaces: How to Add Functionalities while Retaining Effective Antifouling

Spatial control of surface functionalization and interactions is essential for microarray-based analysis. This study reports the fabrication of two-dimensional molecular films with site-specific functionalities, forming microarrays at discrete locations. Arrays of microsized gold disks were produced on a silicate membrane using microfabrication. On these arrays, orthogonal self-assembly of molecules was performed that can specifically bind to gold or silicate. The gold array elements were functionalized with a range of alkanethiols and the silicate with polymeric poly-l-lysine-grafted-poly(ethylene glycol) (PLL-PEG). The surface functionalization on the gold disk array and the surrounding substrate was characterized at each step using X-ray photoelectron spectroscopy (XPS) to show that alkanethiols are specifically attached to the gold. PLL-PEG was used to provide resistance against nonspecific protein and cell adsorption and attached exclusively to the silicate. The effectiveness of the surface chemistry was validated by the selective self-assembly of a gold nanoparticle monolayer array on the gold regions. In a more sophisticated example, selective adhesion of MCF-7 cells to anti-EpCAM antibody modified gold areas of the gold-silicate surface was demonstrated to give a cell microarray. This study provides a general approach to fabricate chemical patterns on silicon-based devices with the convergence of microfabrication and material-specific surface modification, which may be useful to expand the functionalities and potential applications for patterned biomolecular films. Importantly, the ability to pattern surfaces with different surface chemistries is not limited to planar surfaces using this orthogonal surface-coupling approach.

An antifouling coating that enables affinity-based electrochemical biosensing in complex biological fluids

Affinity-based electrochemical detection in complex biological fluids could enable multiplexed point-of-care diagnostics for home healthcare; however, commercialization of point-of-care devices has been limited by the rapid loss of sensitivity caused by electrode surface inactivation and biofouling. Here, we describe a simple and robust antifouling coating for electrodes consisting of a three-dimensional porous matrix of cross-linked bovine serum albumin supported by a network of conductive nanomaterials composed of either gold nanowires, gold nanoparticles or carbon nanotubes. These nanocomposites prevent non-specific interactions while enhancing electron transfer to the electrode surface, preserving 88% of the original signal after 1 month of exposure to unprocessed human plasma, and functionalization with specific antibodies enables quantification of anti-interleukin 6 in plasma with high sensitivity. The easy preparation, stability and simplicity of this nanocomposite allow the generation of electrochemical biosensors that can operate in complex biological fluids such as blood plasma or serum.

Challenges and Opportunities of Carbon Nanomaterials for Biofuel Cells and Supercapacitors: Personalized Energy for Futuristic Self-Sustainable Devices

Various carbon allotropes are fundamental components in electrochemical energy-conversion and energy-storage devices, e.g., biofuel cells (BFCs) and supercapacitors. Recently, biodevices, particularly wearable and implantable devices, are of distinct interest in biomedical, fitness, academic, and industrial fields due to their new fascinating capabilities for personalized applications. However, all biodevices require a sustainable source of energy, bringing widespread attention to energy research. In this review, we detail the progress in BFCs and supercapacitors attributed to carbon materials. Self-powered biosensors for futuristic biomedical applications are also featured. To develop these energy devices, many challenges needed to be addressed. For this reason, there is a need to: optimize the electron transfer between the enzymatic site and electrode; enhance the power efficiency of the device in fluctuating oxygen conditions; strengthen the efficacy of enzymatic reactions at the carbon-based electrodes; increase the electrochemically accessible surface area of the porous electrode materials; and refine the flexibility of traditional devices by introducing a mechanical resiliency of electrochemical devices to withstand daily multiplexed movements. This article will also feature carbon nanomaterial research alongside opportunities to enhance energy technology and address the challenges facing the field of personalized applications. Carbon-based energy devices have proved to be sustainable and compatible energy alternatives for biodevices within the human body, serving as attractive options for further developing diverse domains, including individual biomedical applications.

Lighting Up Biosensors: Now and the Decade To Come

Optical biosensors are defined as portable optical devices that use biorecognition molecules to interrogate a sample for the presence of a target. The capabilities of optical biosensors have expanded rapidly with advances in miniature optical components and molecular engineering. Biosensors to meet the needs in health and environmental monitoring and food safety have become commercially available, with many more in the pipeline. We review the innovative approaches to overcoming existing hurdles to practical biosensor designs and explore potential areas for future breakthroughs in optical biosensor technology.

Tackling the Challenges of Enzymatic (Bio)Fuel Cells

The ever-increasing demands for clean and sustainable energy sources combined with rapid advances in biointegrated portable or implantable electronic devices have stimulated intensive research activities in enzymatic (bio)fuel cells (EFCs). The use of renewable biocatalysts, the utilization of abundant green, safe, and high energy density fuels, together with the capability of working at modest and biocompatible conditions make EFCs promising as next generation alternative power sources. However, the main challenges (low energy density, relatively low power density, poor operational stability, and limited voltage output) hinder future applications of EFCs. This review aims at exploring the underlying mechanism of EFCs and providing possible practical strategies, methodologies and insights to tackle these issues. First, this review summarizes approaches in achieving high energy densities in EFCs, particularly, employing enzyme cascades for the deep/complete oxidation of fuels. Second, strategies for increasing power densities in EFCs, including increasing enzyme activities, facilitating electron transfers, employing nanomaterials, and designing more efficient enzyme-electrode interfaces, are described. The potential of EFCs/(super)capacitor combination is discussed. Third, the review evaluates a range of strategies for improving the stability of EFCs, including the use of different enzyme immobilization approaches, tuning enzyme properties, designing protective matrixes, and using microbial surface displaying enzymes. Fourth, approaches for the improvement of the cell voltage of EFCs are highlighted. Finally, future developments and a prospective on EFCs are envisioned.

Low fouling electrochemical sensing in complex biological media by using the ionic liquid-doped conducting polymer PEDOT: application to voltammetric determination of dopamine

An electrochemical sensor that can resist biofouling even when operated in complex biological medium is developed for the determination of dopamine. It is based on the use of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) that is doped with the water insoluble ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. A glassy carbon electrode modified with PEDOT/IL is shown to enable accurate determination of dopamine, as a model analyte in the presence of high concentrations of proteins, and resist biological fouling even in native serum. It exhibited a low limit of detection of 33 nM for the detection of dopamine, with a wide linear range from 0.2 to 328 μM (at 0.2 V vs. saturated calomel electrode). The PEDOT/IL modified glassy carbon electrode has a porous microstructure, high electrical conductivity and good stability. The sensor can be used to quantify dopamine in human urine samples with satisfying accuracy. Graphical abstract An antifouling electrochemical sensor capable of detecting target in complex biological samples was developed based on the use of a conducting polymer (PEDOT) that was doped with a water insoluble ionic liquid.