Improved operational stability of mediated glucose enzyme electrodes for operation in human physiological solutions

Cross-Linkable Polymer-Based Multi-layers for Protecting Electrochemical Glucose Biosensors against Uric Acid, Ascorbic Acid, and Biofouling Interferences

The lifetime of implantable electrochemical glucose monitoring devices is limited due to the foreign body response and detrimental effects from ascorbic acid (AA) and uric acid (UA) interferents that are components of physiological media. Polymer coatings can be used to shield biosensors from these interferences and prolong their functional lifetime. This work explored several approaches to protect redox polymer-based glucose biosensors against such interferences by designing six targeted multi-layer sensor architectures. Biological interferents, like cells and proteins, and UA and AA interferents were found to have individual effects on the current density and operational stability of glucose biosensors, requiring individual protection and treatment. Protection against biofouling can be achieved using a poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate) (MPC) zwitterionic polymer coating. An enzyme-scavenging approach was compared to electrostatic repulsion by negatively charged polymers for protection against AA and UA interferences. A multi-layer novel polymer design (PD) system consisting of a cross-linkable negatively charged polyvinylimidazole-polysulfostyrene co-polymer inner layer and a cross-linkable MPC zwitterionic polymer outer layer showed the best protection against AA, UA, and biological interferences. The sensor protected using the novel PD shield displayed the lowest mean absolute relative difference between the glucose reading without the interferent and the reading value with the interferent present and also displayed the lowest variability in sensor readings in complex media. For sensor measurements in artificial plasma, the novel PD extends the linear range (R² = 0.99) of the sensor from 0-10 mM for the control to 0-20 mM, shows a smaller decrease in sensitivity, and retains high current densities. The application of PD multi-target coating improves sensor performance in complex media and shows promise for use in sensors operating in real conditions.

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.

Flexible biochemical sensors for point-of-care management of diseases: a review

Health problems have been widely concerned by all mankind. Real-time monitoring of disease-related biomarkers can feedback the physiological status of human body in time, which is very helpful to the diseases management of healthcare. However, conventional non-flexible/rigid biochemical sensors possess low fit and comfort with the human body, hence hindering the accurate and comfortable long-time health monitoring. Flexible and stretchable materials make it possible for sensors to be continuously attached to the human body with good fit, and more precise and higher quality results can be obtained. Thus, tremendous attention has been paid to flexible biochemical sensors in point-of-care (POC) for real-time monitoring the entire disease process. Here, recent progress on flexible biochemical sensors for management of various diseases, focusing on chronic and communicable diseases, is reviewed, and the detection principle and performance of these flexible biochemical sensors are discussed. Finally, some directions and challenges are proposed for further development of flexible biochemical sensors.

A portable solar light-driven biophotoelectrocatalytic system for pollutant removal powered by photovoltaic cells

Photoelectrocatalytic (PEC) technology has been considered as one of the most efficient advanced oxidation processes for wastewater treatment, but the necessity of external electric power supply limits the portability of PEC system for on-field applications. Herein, a portable solar-powered biophotoelectrocatalytic system driven by photovoltaic (PV) cells was explored for degradation of pollutant by coupling BiVO₄/Fe₂O₃-deposited photoanode and horseradish peroxidase (HRP)-immobilized cathode. The integration of PV cells in this PEC device could not only avoid the necessary introduction of external electric power supply, but also improve the utilization of solar irradiation. The characterization of BiVO₄/Fe₂O₃ photoanode demonstrates that ultrathin Fe₂O₃ layer on BiVO₄ electrode could facilitate the holes transfer to the surface efficiently and thus avoid charge recombination. After HRP was immobilized on the cathode, the removal efficiency for 2,4-dichlorophenol (2,4-DCP) was obviously promoted, attributed to the efficient HRP-catalyzed oxidation reaction by in-situ generated H₂O₂ from PEC process. Under natural solar irradiation, the proposed portable biophotoelectrocatalytic device exhibited a satisfying removal efficiency of 92.0% for 100 ppm of 2,4-DCP after 3-h treatment. The intermediate products formed during the degradation process were identified by liquid chromatography-mass spectrometry, and possible 2,4-DCP degradation pathway was also proposed.

Glucose Fuel Cells and Membranes: A Brief Overview and Literature Analysis

Glucose is a ubiquitous source of energy for nearly all living things, and glucose fuel cells (GFCs) are regarded as a sustainable power source because glucose is renewable, easily available, cheap, abundant, non-toxic and easy-to-store. Numerous efforts have been devoted to developing and improving GFC performance; however, there is still no commercially viable devices on the market. Membranes play an essential role in GFCs for the establishment of a suitable local microenvironment, selective ion conducting and prevention of substrate crossover. However, our knowledge on them is still limited, especially on how to achieve comparable efficacy with that of a biological system. This review article provides the first brief overview on these aspects, particularly keeping in sight the research trends, current challenges, and the future prospects. We aim to bring together literature analysis and technological discussion on GFCs and membranes by using bibliometrics, and provide new ideas for researchers in this field to overcome challenges on developing high-performance GFCs.

In vitro enzymatic electrochemical monitoring of glucose metabolism and production in rat primary hepatocytes on highly O2 permeable plates

In situ continuous glucose monitoring under physiological culture conditions is imperative in understanding the dynamics of cell and tissue behaviors and their physiological responses since glucose plays an important role in principal source of biological energy. We therefore examined physiologically relevant dynamic changes in glucose levels based on glucose metabolism and production during aerobic culture (10% O2) of rat primary hepatocytes stimulated with insulin or glucagon on a highly O2 permeable plate, which can maintain the oxygen concentration close to the periportal zone of the liver. As glucose monitoring devices, we used oxygen-independent glucose dehydrogenase-modified single-walled carbon nanotube electrodes placed close to the surface of the hepatocytes. The current response of glucose oxidation slightly decreased after the addition of insulin in the presence of glucose due to the acceleration of glucose uptake by the hepatocytes, whereas that significantly increased after the addition of glucagon and fructose even in the absence of glucose due to the conversion of fructose to glucose based on gluconeogenesis. These phenomena might be consistent relatively with the physiological behaviors of hepatocytes in the periportal region. The present monitoring system would be useful for the studies of glucose homeostasis and diabetes in vitro.

A self-healing carboxymethyl chitosan/oxidized carboxymethyl cellulose hydrogel with fluorescent bioprobes for glucose detection

Self-healing hydrogel as a soft material with high durability and life-time has been successfully applied in various fields, including electronic skins, wearable electronic devices, and soft sensors. However, it is still a challenge to design a hydrogel with rapid self-healing, biodegradable and biosensing properties. Here, a self-healing carboxymethyl chitosan (CMCS)/oxidized carboxymethyl cellulose (OCMC) hydrogel with fluorescent bioprobes was developed for glucose detection. In this biosensing system, gold nanoclusters (AuNCs) and glucose oxidase (GOx) were encapsulated into the CMCS/OCMC hydrogel matrix as the fluorescent bioprobes. The CMCS/OCMC hydrogel with fluorescent bioprobes exhibited high sensitivity for glucose sensing with a linearly detection range of 100 μM to 5 mM and a detection limit of 0.029 mM, which covered the level of glucose in clinical detection. Furthermore, this hydrogel exhibited good biocompatibility. Finally, In vitro blood fluorescence tests and in vivo fluorescence investigation of the AuNCs-CMCS/OCMC hydrogel in diabetic mice indicated that this biocompatible and self-healing hydrogel based on fluorescent sensing system had potential application in implantable biosensing area for glucose monitoring.

Designing a cross-linked redox network for a mediated enzyme-based electrode

A bio-conjugated redox network matrix based on glucose dehydrogenase, thionine (diamine-containing mediator), and poly(ethylene glycol) diglycidyl ether (crosslinker) is developed on a glassy carbon electrode through covalent bonding with one-pot crosslinking. Electrons from the enzyme diffuse through the network producing 400 μA cm-2 of glucose oxidation current at 25 °C.

Utilization of FAD-Glucose Dehydrogenase from T. emersonii for Amperometric Biosensing and Biofuel Cell Devices

Flavin-dependent glucose dehydrogenases (FAD-GDH) are oxygen-independent enzymes with high potential to be used as biocatalysts in glucose biosensing applications. Here, we present the construction of an amperometric biosensor and a biofuel cell device, which are based on a thermophilic variant of the enzyme originated from Talaromyces emersonii. The enzyme overexpression in Escherichia coli and its isolation and performance in terms of maximal bioelectrocatalytic currents were evaluated. We examined the biosensor's bioelectrocatalytic activity in 2,6-dichlorophenolindophenol-, thionine-, and dichloro-naphthoquinone-mediated electron transfer configurations or in a direct electron transfer one. We showed a negligible interference effect and good stability for at least 20 h for the dichloro-naphthoquinone configuration. The constructed biosensor was also tested in interstitial fluid-like solutions to show high bioelectrocatalytic current responses. The bioanode was coupled with a bilirubin oxidase-based biocathode to generate 270 μW/cm2 in a biofuel cell device.

Self-Powered Detection of Glucose by Enzymatic Glucose/Oxygen Fuel Cells on Printed Circuit Boards

Monitoring glucose levels in physiological fluids can help prevent severe complications associated with hypo- and hyper-glycemic events. Current glucose-monitoring systems require a three-electrode setup and a power source to function, which can hamper the system miniaturization to the patient discomfort. Enzymatic fuel cells (EFCs) offer the opportunity to develop self-powered and minimally invasive glucose sensors by eliminating the need for an external power source. Nevertheless, practical applications demand for cost-effective and mass-manufacturable EFCs compatible with integration strategies. In this study, we explore for the first time the use of gold electrodes on a printed circuit board (PCB) for the development of an EFC and demonstrate its application in saliva. To increase the specific surface area, the PCB gold-plated electrodes were modified with porous gold films. At the anode, glucose oxidase is immobilized with an osmium redox polymer that serves as an electron-transfer mediator. At the cathode, bilirubin oxidase is adsorbed onto the porous gold surface with a blocking agent that prevents parasitic reactions while maintaining the enzyme catalytic activity. The resulting EFC showed a linear response to glucose in phosphate buffer within the range 50 μM to 1 mM, with a sensitivity of 14.13 μA cm-2 mM-1. The sensor was further characterized in saliva, showing the linear range of detection of 0.75 to 2 mM, which is within the physiological range, and sensitivity of 21.5 μA cm-2 mM-1. Overall, this work demonstrates that PCBs are suitable platforms for EFCs, paving the way for the development of fully integrated systems in a seamless and miniaturized device.

Electrochemical monitoring of alcohol in sweat

Rapid, periodic monitoring and detection of ethanol (EtOH) after consumption via a non-invasive measurement has been an area of increased research in recent years. Current point-of-care or on-site detection strategies rely on single use sensors which are inadequate for monitoring during a longer period. A low cost, portable and novel approach is developed here for real-time monitoring over several days utilising electrochemical techniques. The sensor shows oxidation of the ethanol in phosphate buffer and artificial sweat using the amperometric response from the application of +0.9 V to the polyaniline modified screen printed electrode using 1 mM EtOH as the averaged amount of EtOH eliminated in sweat after the consumption of one alcoholic beverage. Our enzyme based electrochemical sensor exhibits a qualitative assessment of the presence of EtOH in small volumes (≤40 μL) of 0.1 M sodium bicarbonate and subsequently artificial sweat, with 50 measurements taken daily over 11 days. While quantitative information is not obtained, the sensor system exhibits excellent stability after 3 months' dried storage in this complex biological matrix in an oxygen free cabinet. This addresses one of the key challenges for enzyme based electrochemical sensors, namely, the ability for real-time monitoring in complex biological matrices. The qualitative response illustrates the potential for this sensor to be exploited by non-experts which suggests the promise for their wider application in next-generation wearable electronics necessary for alcohol monitoring.