Co-immobilization of glucose oxidase and hexokinase on silicate hybrid sol-gel membrane for glucose and ATP detections

Bioelectrochemical biosensors for water quality assessment and wastewater monitoring

Bioelectrochemical biosensors offer a promising approach for real-time monitoring of industrial bioprocesses. Many bioelectrochemical biosensors do not require additional labelling reagents for target molecules. This simplifies the monitoring process, reduces costs, and minimizes potential contamination risks. Advancements in materials science and microfabrication technologies are paving the way for smaller, more portable bioelectrochemical biosensors. This opens doors for integration into existing bioprocessing equipment and facilitates on-site, real-time monitoring capabilities. Biosensors can be designed to detect specific heavy metals such as lead, mercury, or chromium in wastewater. Early detection allows for the implementation of appropriate removal techniques before they reach the environment. Despite these challenges, bioelectrochemical biosensors offer a significant leap forward in wastewater monitoring. As research continues to improve their robustness, selectivity, and cost-effectiveness, they have the potential to become a cornerstone of efficient and sustainable wastewater treatment practices.

Biomimetic Sol-Gel Chemistry to Tailor Structure, Properties, and Functionality of Bionanocomposites by Biopolymers and Cells

Biosilica, synthesized annually only by diatoms, is almost 1000 times more abundant than industrial silica. Biosilicification occurs at a high rate, although the concentration of silicic acid in natural waters is ~100 μM. It occurs in neutral aqueous solutions, at ambient temperature, and under the control of proteins that determine the formation of hierarchically organized structures. Using diatoms as an example, the fundamental differences between biosilicification and traditional sol-gel technology, which is performed with the addition of acid/alkali, organic solvents and heating, have been identified. The conditions are harsh for the biomaterial, as they cause protein denaturation and cell death. Numerous attempts are being made to bring sol-gel technology closer to biomineralization processes. Biomimetic synthesis must be conducted at physiological pH, room temperature, and without the addition of organic solvents. To date, significant progress has been made in approaching these requirements. The review presents a critical analysis of the approaches proposed to date for the silicification of biomacromolecules and cells, the formation of bionanocomposites with controlled structure, porosity, and functionality determined by the biomaterial. They demonstrated the broad capabilities and prospects of biomimetic methods for creating optical and photonic materials, adsorbents, catalysts and biocatalysts, sensors and biosensors, and biomaterials for biomedicine.

The Evolving Role of Proteins in Wearable Sweat Biosensors

Sweat is an increasingly popular biological medium for fitness monitoring and clinical diagnostics. It contains an abundance of biological information and is available continuously and noninvasively. Sweat-sensing devices often employ proteins in various capacities to create skin-friendly matrices that accurately extract valuable and time-sensitive information from sweat. Proteins were first used in sensors as biorecognition elements in the form of enzymes and antibodies, which are now being tuned to operate at ranges relevant for sweat. In addition, a range of structural proteins, sometimes assembled in conjunction with polymers, can provide flexible and compatible matrices for skin sensors. Other proteins also naturally possess a range of functionalities─as adhesives, charge conductors, fluorescence emitters, and power generators─that can make them useful components in wearable devices. Here, we examine the four main components of wearable sweat sensors─the biorecognition element, the transducer, the scaffold, and the adhesive─and the roles that proteins have played so far, or promise to play in the future, in each component. On a case-by-case basis, we analyze the performance characteristics of existing protein-based devices, their applicable ranges of detection, their transduction mechanism and their mechanical properties. Thereby, we review and compare proteins that can readily be used in sweat sensors and others that will require further efforts to overcome design, stability or scalability challenges. Incorporating proteins in one or multiple components of sweat sensors could lead to the development and deployment of tunable, greener, and safer biosourced devices.

Bi-enzyme competition based on ZIF-67 co-immobilization for real-time monitoring of exocellular ATP

Monitoring exocellular adenosine-5'-triphosphate (ATP) is a demanding task but the biosensor development is limited by the low concentration and rapid degradation of ATP. Herein, we developed a simple yet effective biosensor based on ZIF-67 loaded with bi-enzymes of glucose (GOx) and hexokinase (HEX) for effective detection of ATP. In the confined space of the porous matrix, the bi-enzymes competed for the glucose substrate in the presence of ATP, facilitating the biosensor to detect low ATP concentrations down to the micromole level (3.75 μM) at working potential of 0.55 V (vs. Ag/AgCl). Furthermore, ZIF-67 with cobalt served as a porous matrix to specifically adsorb ATP molecules, allowing it to differentiate isomers with sensitivity of 0.53 nA/μM, RSD of 5.4%, and recovery rate of 93.3%. We successfully applied the fabricated biosensor to measure ATP secreted from rat PC12 cells in the pericellular space thus realizing time-resolving measurement. This work paved the path for real-time monitoring of ATP released by cells, which will aid in understanding tumor cell glycolysis and immune responses.

CMOS-Based Redox-Type Label-Free ATP Image Sensor for In Vitro Sensitive Imaging of Extracellular ATP

Adenosine 5'-triphosphate (ATP) plays a crucial role as an extracellular signaling molecule in the central nervous system and is closely related to various nerve diseases. Therefore, label-free imaging of extracellular ATP dynamics and spatiotemporal analysis is crucial for understanding brain function. To decrease the limit of detection (LOD) of imaging extracellular ATP, we fabricated a redox-type label-free ATP image sensor by immobilizing glycerol-kinase (GK), L-α-glycerophosphate oxidase (LGOx), and horseradish peroxidase (HRP) enzymes in a polymer film on a gold electrode-modified potentiometric sensor array with a 37.3 µm-pitch. Hydrogen peroxide (H₂O₂) is generated through the enzymatic reactions from GK to LGOx in the presence of ATP and glycerol, and ATP can be detected as changes in its concentration using an electron mediator. Using this approach, the LOD for ATP was 2.8 µM with a sensitivity of 77 ± 3.8 mV/dec., under 10 mM working buffers at physiological pH, such as in in vitro experiments, and the LOD was great superior 100 times than that of the hydrogen ion detection-based image sensor. This redox-type ATP image sensor may be successfully applied for in vitro sensitive imaging of extracellular ATP dynamics in brain nerve tissue or cells.

Smartphone-based colorimetric detection systems for glucose monitoring in the diagnosis and management of diabetes

Diabetes is a group of metabolic conditions resulting in high blood sugar levels over prolonged periods that affects hundreds of millions of patients worldwide. Measuring glucose concentration enables patient-specific insulin therapy, and is essential to reduce the severity of the disease, potential complications, and related mortalities. Recent advances and developments in smartphone-based colorimetric glucose detection systems are discussed in this review. The importance of glucose monitoring, data collection, transfer, and analysis, via non-invasive/invasive methods is highlighted. The review also presents various approaches using 3D-printed materials, screen-printed electrodes, polymer templates, designs allowing multiple glucose analysis, bioanalytes and/or nanostructures for glucose detection. The positive effects of advances in improving the performance of smartphone-based platforms are introduced along with future directions and trends in the application of emerging technologies in smartphone-based diagnostics.

Synthesis of a novel hedgehog-shaped Bi2S3 nanostructure for a sensitive electrochemical glucose biosensor

A novel hedgehog-shaped Bi2S3 nanostructure was synthesized using a simple hydrothermal route with a composite soft template and further used to construct a sensitive glucose biosensor.

Electrochemical biosensors based on multienzyme systems: Main groups, advantages and limitations - A review

In the review, the principles and main purposes of using multienzyme systems in electrochemical biosensors are analyzed. Coupling several enzymes allows an extension of the spectrum of detectable substances, an increase in the biosensor sensitivity (in some cases, by several orders of magnitude), and an improvement of the biosensor selectivity, as showed on the examples of amperometric, potentiometric, and conductometric biosensors. The biosensors based on cascade, cyclic and competitive enzyme systems are described alongside principles of function, advantages, disadvantages and practical use for real sample analyses in various application areas (food production and quality control, clinical diagnostics, environmental monitoring). The complications and restrictions regarding the development of multienzyme biosensors are evaluated. The recommendations on the reasonability of elaboration of novel multienzyme biosensors are given.

3D bimetallic Au/Pt nanoflowers decorated needle-type microelectrode for direct in situ monitoring of ATP secreted from living cells

Adenosine triphosphate (ATP) plays a crucial role in energy metabolism and extracellular purinergic signaling. A 3D bimetallic Au/Pt nanoflowers decorated ATP microelectrode biosensor prepared by facile and effective template-free electrodeposition was firstly reported, realizing local detection of cellular ATP secretion. The ATP biosensor was developed by co-immobilization of glucose oxidase and hexokinase, exhibiting long-term stability (79.39 ± 9.15% of its initial value remained after 14 days at 4 °C) and high selectivity with a limit of detection down to 2.5 μM (S/N = 3). The resulting ATP biosensor was then used for direct in situ monitoring of ATP secreted from living cells (PC12) with the stimulation of high K⁺ solutions. The obtained current was about 21.6 ± 3.4 nA (N = 6), corresponding to 12.2 ± 2.8 μM ATP released from cells, right in the micromolar range and consistent with the suggested levels. The 3D bimetallic Au/Pt nanoflowers possess excellent catalytic activity and large electroactive surface area, contributing to enzymatic activity preservation and long-term stability. This work provides a promising platform for long-time monitoring of other neurotransmitters and secretions in cellular glycolysis and apoptosis processes in the future.

Simultaneous Detection of Adenosine Triphosphate and Glucose Based on the Cu-Fenton Reaction

Both adenosine triphosphate (ATP) and glucose are important to human health, and their abnormal levels are closely related to angiocardiopathy and hypoglycaemia. Therefore, the simultaneous determination of ATP and glucose with a single test mode is highly desirable for disease diagnostics and early recognition. Herein, a new fluorescence on/off switch sensing platform is developed by carbon nanodots (CNDs) to detect ATP and glucose simultaneously. The fluorescence of CNDs can be quenched by Cu²⁺ and hydrogen peroxide (H₂O₂), due to the formation of hydroxyl radicals (·OH) produced in the Cu-Fenton reaction. Based on the high affinity of Cu²⁺ with ATP, the fluorescence of CNDs will recover effectively after adding ATP. Additionally, glucose can be efficiently catalyzed by glucose oxidase (GOx) to generate H₂O₂, so the platform can also be utilized to analyze glucose. Under optimum conditions, this sensing platform displays excellent sensitivity and the linear ranges are from 0.1 to 7 μM for ATP with a limit of detection (LOD) of 30.2 nM, and from 0.1 to 7 mM for glucose with a LOD 39.8 μM, respectively. Benefiting from the high sensitivity and selectivity, this sensing platform is successfully applied for simultaneous detection of ATP and glucose in human serum samples with satisfactory recoveries.

An investigation into closed-loop treatment of neurological disorders based on sensing mitochondrial dysfunction

Dynamic feedback based closed-loop medical devices offer a number of advantages for treatment of heterogeneous neurological conditions. Closed-loop devices integrate a level of neurobiological feedback, which allows for real-time adjustments to be made with the overarching aim of improving treatment efficacy and minimizing risks for adverse events. One target which has not been extensively explored as a potential feedback component in closed-loop therapies is mitochondrial function. Several neurodegenerative and psychiatric disorders including Parkinson's disease, Major Depressive disorder and Bipolar disorder have been linked to perturbations in the mitochondrial respiratory chain. This paper investigates the potential to monitor this mitochondrial function as a method of feedback for closed-loop neuromodulation treatments. A generic model of the closed-loop treatment is developed to describe the high-level functions of any system designed to control neural function based on mitochondrial response to stimulation, simplifying comparison and future meta-analysis. This model has four key functional components including: a sensor, signal manipulator, controller and effector. Each of these components are described and several potential technologies for each are investigated. While some of these candidate technologies are quite mature, there are still technological gaps remaining. The field of closed-loop medical devices is rapidly evolving, and whilst there is a lot of interest in this area, widespread adoption has not yet been achieved due to several remaining technological hurdles. However, the significant therapeutic benefits offered by this technology mean that this will be an active area for research for years to come.

A novel conductometric biosensor based on hexokinase for determination of adenosine triphosphate

The paper presents a simple and inexpensive reusable biosensor for determination of the concentration of adenosine-5'-triphosphate (ATP) in aqueous samples. The biosensor is based on a conductometric transducer which contains two pairs of gold interdigitated electrodes. An enzyme hexokinase was immobilized onto one pair of electrodes, and bovine serum albumin-onto another pair (thus, a differential mode of measurement was used). Conditions of hexokinase immobilization on the transducer by cross-linking via glutaraldehyde were optimized. Influence of experimental conditions (concentration of magnesium ions, ionic strength and concentration of the working buffer) on the biosensor work was studied. The reproducibility of biosensor responses and operational stability of the biosensor were checked during one week. Dry storage at -18 °C was shown to be the best conditions to store the biosensor. The biosensor was successfully applied for measurements of ATP concentration in pharmaceutical samples. The proposed biosensor may be used in future for determination of ATP and/or glucose in water samples.

Amperometric biosensor system for simultaneous determination of adenosine-5'-triphosphate and glucose

The majority of biosensors for adenosine-5'-triphosphate (ATP) determination are based on cascades of enzymatic reactions; therefore, they are sensitive to glucose or glycerol (depending on the enzymatic system) as well as to ATP. The presence of unknown concentrations of these substances in the sample greatly complicates the determination of ATP. To overcome this disadvantage of known biosensors, we developed a biosensor system consisting of two biosensors: the first one is based on glucose oxidase and is intended for measuring glucose concentration, and the second one is based on glucose oxidase and hexokinase and is sensitive toward both glucose and ATP. Using glucose concentration measured by the first biosensor, we can analyze the total response to glucose and ATP obtained by the second biosensor. Platinum disc electrodes were used as amperometric transducers. The polyphenilenediamine membrane was deposited onto the surface of platinum electrodes to avoid the response to electroactive substances. The effect of glucose concentration on biosensor determination of ATP was studied. The reproducibility of biosensor responses to glucose and ATP during a day was tested (relative standard deviation, RSD, of responses to glucose was 3-6% and to ATP was 8-12%) as well as storage stability of the biosensors (no decrease of glucose responses and 43% drop of ATP responses during 50 days). The measurements of ATP and glucose in pharmaceutical vials (including mixtures of ATP and glucose) were carried out. It was shown that the developed biosensor system can be used for simultaneous analysis of glucose and ATP concentrations in water solutions.

Immobilization and applications of glucose-6-phosphate dehydrogenase: a review

Immobilized enzymes have been used extensively in the fields of food industry, materials processing, textiles, detergents, biochemical and chemical industries, biotechnology, and pharmaceuticals. Studies on immobilization of glucose-6-phosphate dehydrogenase have been less extensive than those for other industrially applicable enzymes. Immobilization of glucose-6-phosphate dehydrogenase has been carried out for the formation of biosensors for the estimation of glucose, ATP, phosphate, and so on. The present review deals with the attempts made for immobilization of glucose-6-phosphate dehydrogenase and its applications for various purposes.

Monolayer-protected nanoparticle doped xerogels as functional components of amperometric glucose biosensors

First-generation amperometric glucose biosensors incorporating alkanethiolate-protected gold nanoparticles, monolayer protected clusters (MPCs), within a xerogel matrix are investigated as model systems for nanomaterial-assisted electrochemical sensing strategies. The xerogel biosensors are comprised of platinum electrodes modified with composite films of (3-mercaptopropyl)trimethoxy silane xerogel embedded with glucose oxidase enzyme, doped with Au225(C6)75 MPCs, and coated with an outer polyurethane layer. Electrochemistry and scanning/transmission electron microscopy, including cross-sectional TEM, show sensor construction, humidity effects on xerogel structure, and successful incorporation of MPCs. Analytical performance of the biosensor scheme with and without MPC doping of the xerogel is determined from direct glucose injection during amperometry. MPC-doped xerogels yield significant enhancement of several sensor attributes compared to analogous films without nanoparticles: doubling of the linear range, sensitivity enhancement by an order of magnitude, and 4-fold faster response times accompany long-term stability and resistance to common interfering agents that are competitive with current glucose biosensing literature. Ligand chain length and the MPC/silane ratio studies suggest the MPC-induced enhancements are critically related to structure-function relationships, particularly those affecting interparticle electronic communication where the MPC network behaves as a three-dimensional extension of the working electrode into the xerogel film, reducing the system's dependence on diffusion and maximizing efficiency of the sensing mechanism. The integration of MPCs as a functional component of amperometric biosensor schemes has implications for future development of biosensors targeting clinically relevant species.

Enzyme immobilization by entrapment within a gel network

This chapter provides a detailed description of the three immobilization methods based on the biomolecules entrapment into polymer matrices. The poly (vinyl alcohol) bearing styrylpyridinium groups (PVA-SbQ), a soluble pre-polymer bearing photo-cross-linkable groups, has widely been used to entrap enzymes, and several bioassays based on this immobilization matrix have been reported. Similarly, immobilization of enzymes via sol-gel has been described in this chapter. Sol-gel process is based on the ability to form solid metal or semi-metal oxides via the aqueous process of hydrolytically labile precursors. Enzymes can also be entrapped in an agarose gel. Contrary to synthetic polymers such as polyacrylamide, this matrix is biocompatible, non-toxic, provides natural microenvironment to the enzyme and also gives sufficient accessibility to electrons to shuttle between the enzyme and the electrode. The entrapment strategies are easy-to-perform, and permit to deposit enzyme, mediators, and additives in the same sensing layer. Moreover, the activity of the enzyme is preserved during the immobilization process, as biological element is not modified. Biosensors based on physically entrapped enzymes are often characterized by increased operational and storage stability.

Durable cofactor immobilization in sol-gel bio-composite thin films for reagentless biosensors and bioreactors using dehydrogenases

A new strategy directed to the durable immobilization of NAD(+)/NADH cofactors has been tested, along with a suitable redox mediator (ferrocene), in biocompatible sol-gel matrices encapsulating a bi-enzymatic system (a dehydrogenase and a diaphorase, this latter being useful to the safe regeneration of the cofactor), which were deposited as thin films onto glassy carbon electrode surfaces. It involves the chemical attachment of NAD(+) to the silica matrix using glycidoxypropylsilane in the course of the sol-gel process (in smooth chemical conditions). This approach based on chemical bonding of the cofactor (which was checked by infrared spectroscopy) led to good performances in terms of long-term stability of the electrochemical response. The possibility to integrate all components (proteins, cofactor, mediator) in the sol-gel layer in an active and durable form gave rise to reagentless devices with extended operational stability (i.e. high amperometric response maintained for more than 12h of continuous use under constant potential, whereas the signal completely vanished within the first few minutes of working with non-covalently bonded NAD(+)). To confirm the wide applicability of the proposed approach, the same strategy has been applied to the elaboration of biosensors for D-sorbitol, D-glucose and L-lactate with using D-sorbitol dehydrogenase, D-glucose dehydrogenase and L-lactate dehydrogenase respectively. The analytical characteristics of the glucose sensors are given and compared to previous approaches described in the literature for the elaboration of reagentless biosensors.

A High Throughput and High Selective Chemiluminescence Method for Quantification of Bifenthrin Based on Molecularly Imprinted Film

One novel highly cross-linked, shape-controllable molecularly imprinted sol-gel film (MISF) with good thermal and chemical stability and three-dimensional network porous structure has been developed. The binding characteristic of the imprinted film to bifenthrin was evaluated by equilibrium binding experiments and imprinting-induced promotion of binding. The MISF was modified into the wells of 96 micro-well plate combined with chemiluminescence (CL) technology to establish the molecular imprinting-chemiluminescence (MI-CL) sensor. The high throughput and high selective detection sensor of bifenthrin was applied in vegetable and food samples with satisfactory results.

Co-immobilized coupled enzyme systems in biotechnology

The development of coimmobilized multi-enzymatic systems is increasingly driven by economic and environmental constraints that provide an impetus to develop alternatives to conventional multistep synthetic methods. As in nature, enzyme-based systems work cooperatively to direct the formation of desired products within the defined compartmentalization of a cell. In an attempt to mimic biology, coimmobilization is intended to immobilize a number of sequential or cooperating biocatalysts on the same support to impart stability and enhance reaction kinetics by optimizing catalytic turnover. There are three primary reasons for the utilization of coimmobilized enzymes: to enhance the efficiency of one of the enzymes by the in-situ generation of its substrate, to simplify a process that is conventionally carried out in several steps and/or to eliminate undesired by-products of an enzymatic reaction. As such, coimmobilization provides benefits that span numerous biotechnological applications, from biosensing of molecules to cofactor recycling and to combination of multiple biocatalysts for the synthesis of valuable products.

ATP microelectrode biosensor for stable long-term in vitro monitoring from gastrointestinal tissue

We have developed a stable and selective ATP biosensor for long-term in vitro tissue monitoring. The electrode was fabricated by entrapping glucose oxidase (GOx) and hexokinase (HEX) in a poly-phenol film on a Pt microelectrode. The biosensor was stable to a fixed concentration of glucose for over 20 min and had a limit of detection of 9.9 ± 3.2 nM, with a sensitivity of 45.8 ± 1.22 pA μM(-1). Most significantly of all, the response on the ATP biosensor did not alter in the presence of 1mM ascorbic acid, 5 μM dopamine, 5 μM serotonin, 5 μM ADP and 5 μM AMP. The ATP biosensor was also shown to have excellent stability over 7 days, and showed only a 23.92 ± 3.55% loss in sensitivity. The ATP biosensor was utilised for the in vitro detection of ATP from gastrointestinal tissue. The ATP biosensor response was stable for 5h during in vitro recordings from ileum tissue. ATP release was shown to be greater from the mucosal surface in the ileum compared to the colon.

Review of recent advances in analytical techniques for the determination of neurotransmitters

Methods and advances for monitoring neurotransmitters in vivo or for tissue analysis of neurotransmitters over the last five years are reviewed. The review is organized primarily by neurotransmitter type. Transmitter and related compounds may be monitored by either in vivo sampling coupled to analytical methods or implanted sensors. Sampling is primarily performed using microdialysis, but low-flow push-pull perfusion may offer advantages of spatial resolution while minimizing the tissue disruption associated with higher flow rates. Analytical techniques coupled to these sampling methods include liquid chromatography, capillary electrophoresis, enzyme assays, sensors, and mass spectrometry. Methods for the detection of amino acid, monoamine, neuropeptide, acetylcholine, nucleoside, and soluble gas neurotransmitters have been developed and improved upon. Advances in the speed and sensitivity of these methods have enabled improvements in temporal resolution and increased the number of compounds detectable. Similar advances have enabled improved detection at tissue samples, with a substantial emphasis on single cell and other small samples. Sensors provide excellent temporal and spatial resolution for in vivo monitoring. Advances in application to catecholamines, indoleamines, and amino acids have been prominent. Improvements in stability, sensitivity, and selectivity of the sensors have been of paramount interest.

Development of DNA electrochemical biosensor based on covalent immobilization of probe DNA by direct coupling of sol-gel and self-assembly technologies

A new procedure for fabricating deoxyribonucleic acid (DNA) electrochemical biosensor was developed based on covalent immobilization of target single-stranded DNA (ssDNA) on Au electrode that had been functionalized by direct coupling of sol-gel and self-assembled technologies. Two siloxanes, 3-mercaptopropyltrimethoxysiloxane (MPTMS) and 3-glycidoxypropyltrimethoxysiloxane (GPTMS) were used as precursors to prepare functionally self-assembly sol-gel film on Au electrode. The thiol group of MPTMS allowed assembly of MPTMS sol-gel on gold electrode surface. Through co-condensation between silanols, GPTMS sol-gel with epoxide groups interconnected into MPTMS sol-gel and enabled covalent immobilization of target NH(2)-ssDNA through epoxide/amine coupling reaction. The concentration of MPTMS and GPTMS influenced the performance of the resulting biosensor due to competitive sol-gel process. The linear range of the developed biosensor for determination of complementary ssDNA was from 2.51 x 10(-9) to 5.02 x 10(-7)M with a detection limit of 8.57 x 10(-10)M. The fabricated biosensor possessed good selectivity and could be regenerated. The covalent immobilization of target ssDNA on self-assembled sol-gel matrix could serve as a versatile platform for DNA immobilization and fabrication of biosensors.