NAD(P)-dependent glucose dehydrogenase: Applications for biosensors, bioelectrodes, and biofuel cells

Low-overpotential and highly sensitive detection of NADH with electrochemically pretreated cup-stacked carbon nanofiber electrodes

Cup-stacked carbon nanofibers (CSCNFs), the surface of which provides highly ordered graphene edges and electroactive oxygen-containing functional groups, were investigated as electrode materials for oxidation of β-Nicotinamide adenine dinucleotide (NADH) at low overpotential. The NADH oxidation was facilitated at the CSCNF-modified glassy carbon (CSCNF/GC) electrode, the surface of which was electrochemically activated at -0.40 V (vs. Ag|AgCl) to generate electrochemically reduced electroactive oxygen-containing functional groups. The anodic peak current of NADH oxidation was observed at about + 0.065 V by cyclic voltammetry measurements. The obtained value was negatively shifted by ~ 0.33 and ~ 0.63 V compared with the CSCNF/GC electrode without the electrochemical reductive pretreatment and the GC electrode, respectively. In addition, NADH-dependent glucose dehydrogenase (GDH) molecule-modified CSCNF/GC electrodes enabled the detection of glucose at the low overpotential effectively in the presence of NAD+, which accepts electrons from GDH and then reduces to NADH, after the electrochemical reductive pretreatment. Thus, the electrochemical reductive pretreatment of CSCNF electrodes would be useful for the development of highly sensitive NADH-dependent enzymatic biosensors.

Enhancing Bacillus cereus antibacterial ability through improved cofactor supply

Bacillus cereus 0-9 is a biocontrol microorganism that antagonizes Gram-positive bacteria and pathogenic fungi, such as Staphylococcus aureus and Gaeumannomyces graminis, through the secretion of antimicrobial peptides. However, its low antibacterial activity limits its biocontrol application. In this study, a significant enhancement in antibacterial activity against S. aureus was achieved by overexpressing glucose dehydrogenase from Bacillus subtilis (BsGDH) in B. cereus 0-9, expanding the activity from 6.98 to 11.59 U/mL, representing a 66% improvement. To further improve its biocontrol capability, we aimed to improve the catalytic efficiency of BsGDH by screening 11 low-conserved residues in the protein's second-shell via conservation analysis and molecular docking. Following three rounds of saturation mutagenesis, the specific enzyme activity and Kcat/Km value of the variant N97F/N192S/E198G reached to 289.74 U/mg and 4.95 µM⁻¹·min⁻¹, representing 5.66 and 11.38 times greater than that of the wild-type BsGDH, respectively. Molecular docking suggested that residues Gly94, Gly14, and Ile191 form a triangular region enhancing substrate affinity and enzymatic activity. Furthermore, the Root Mean Square Fluctuation analysis from molecular dynamics showed significant conformational changes in five regions of the mutants (α2 helix, α3 helix, α5 helix + β4 sheet, α8 helix + β5 sheet, and α13-14 helix), increasing the flexibility of the active pocket. Ultimately, the antibacterial activity of B. cereus 0-9 expressing N97F/N192S/E198G reached 22.79 U/mL, 2.26 times higher than that of B. cereus 0-9. This study offers a promising candidate for enhancing NAD(P)+ metabolic cycling and antimicrobial peptide synthesis in cells for industrial applications.

Synergistic optimization strategies for the development of multienzymatic cascade system-based electrochemical biosensors with enhanced performance

Multienzymatic cascade system (MCS) strategies have been a topic of growing interest in the electrochemical biosensor research field owing to their many advantages. By combining two or more enzymes in an appropriate manner, MCS approaches can extend the range of detection for particular analytes while improving the overall efficiency of biocatalytic cascade reactions. Compared with mono-enzyme biosensors, the integration of MCS and electrochemical biosensor platforms is inherently more challenging owing to the increased complexity of the resultant system. In recent years, substantial progress in the development of MCS-based electrochemical biosensors with enhanced analytical performance has been made. This review provides an overview of the types of MCS strategies and their biosensor applications, together with a summary of synergistic optimization approaches that can help improve key parameters including sensitivity, selectivity, and stability when designing MCS-based electrochemical biosensors. These discussions include examples of published biosensor platforms (2016-2024) while also surveying key advances in associated research areas including redox mediators/enzyme co-immobilization, enzyme engineering, multienzyme spatial regulation, enzyme-nanozyme integration and others. Lastly, a brief overview of current challenges and future perspectives pertaining to MCS-based electrochemical biosensor design is provided.

Enzyme-Enabled Droplet Biobattery for Powering Synthetic Tissues

Enzyme-enabled biobatteries are promising green options to power the next-generation of bioelectronics and implantable medical devices. However, existing power sources based on enzymatic biofuel chemistry exhibit limited scale-down feasibility due to the solid and bulky battery structures. Therefore, miniature and soft alternatives are needed for integration with implants and tissues. Here, a biobattery built from nanolitre droplets, fuelled by the enzyme-enabled oxidation of reduced nicotinamide adenine dinucleotide, generates electrical outputs and powers ion fluxes in droplet networks. Optimization of the droplet biobattery components ensures a stable output current of ~13,000 pA for over 24 h, representing a more than 600-fold increase in output over previous approaches, including light-driven processes. The enzyme-enabled droplet biobattery opens new avenues in bioelectronics and bioiontronics, exemplified by tasks such as the ability to drive chemical signal transmission in integrated synthetic tissues.

Glucose Oxidase-Based Glucose Biosensing with a Simple Dual Ag/AgCl Probe Conductivity Readout

We describe a conductometric assay of the enzymatic conversion of glucose to gluconic acid by dissolved glucose oxidase (GOx), using the generation of proton and gluconate from the reaction product dissociation for glucose detection. Simple basics of ionic conductivity, a silver/silver chloride wire pair, and a small applied potential translate glucose-dependent GOx activity into a scalable cell current. Enzyme immobilization and complex sensor design, involving extra nanomaterials or microfabrication of electrode structures, are entirely avoided, in contrast to all modern electrochemical glucose biosensors. Assay calibration showed a response linearity up to 500 μM, with a sensitivity of about 1.3 nA/μM. Selectivity tests excluded signals from sugars other than glucose, and glucose quantifications with recovery rates close to 100% were reached with a model sample and a beverage. Easy use of elementary physicochemical phenomena and a satisfactory performance are assets of the proposed non-amperometric glucose biosensing strategy. Assay integration into a planar dual electrode platform, with or without microfluidic application option, is feasible because of the simplicity of the sensor readout and suggests a route to affordable glucose analysis in beverage, food, and body fluid samples.

Does Acinetobacter calcoaceticus glucose dehydrogenase produce self-damaging H2O2?

The soluble glucose dehydrogenase (sGDH) from Acinetobacter calcoaceticus has been widely studied and is used, in biosensors, to detect the presence of glucose, taking advantage of its high turnover and insensitivity to molecular oxygen. This approach, however, presents two drawbacks: the enzyme has broad substrate specificity (leading to imprecise blood glucose measurements) and shows instability over time (inferior to other oxidizing glucose enzymes). We report the characterization of two sGDH mutants: the single mutant Y343F and the double mutant D143E/Y343F. The mutants present enzyme selectivity and specificity of 1.2 (Y343F) and 5.7 (D143E/Y343F) times higher for glucose compared with that of the wild-type. Crystallographic experiments, designed to characterize these mutants, surprisingly revealed that the prosthetic group PQQ (pyrroloquinoline quinone), essential for the enzymatic activity, is in a cleaved form for both wild-type and mutant structures. We provide evidence suggesting that the sGDH produces H2O2, the level of production depending on the mutation. In addition, spectroscopic experiments allowed us to follow the self-degradation of the prosthetic group and the disappearance of sGDH's glucose oxidation activity. These studies suggest that the enzyme is sensitive to its self-production of H2O2. We show that the premature aging of sGDH can be slowed down by adding catalase to consume the H2O2 produced, allowing the design of a more stable biosensor over time. Our research opens questions about the mechanism of H2O2 production and the physiological role of this activity by sGDH.

Synthesis of Chiral Sulfoxides by A Cyclic Oxidation-Reduction Multi-Enzymatic Cascade Biocatalysis

Optically pure sulfoxides are valuable organosulfur compounds extensively employed in medicinal and organic synthesis. In this study, we present a biocatalytic oxidation-reduction cascade system designed for the preparation of enantiopure sulfoxides. The system involves the cooperation of a low-enantioselective chimeric oxidase SMO (styrene monooxygenase) with a high-enantioselective reductase MsrA (methionine sulfoxide reductase A), facilitating "non-selective oxidation and selective reduction" cycles for prochiral sulfide oxidation. The regeneration of requisite cofactors for MsrA and SMO was achieved via a cascade catalysis process involving three auxiliary enzymes, sustained by cost-effective D-glucose. Under the optimal reaction conditions, a series of heteroaryl alkyl, aryl alkyl and dialkyl sulfoxides in R configuration were synthesized through this "one-pot, one step" cascade reaction. The obtained compounds exhibited high yields of >90 % and demonstrated enantiomeric excess (ee) values exceeding 90 %. This study represents an unconventional and efficient biocatalytic way in utilizing the low-enantioselective oxidase for the synthesis of enantiopure sulfoxides.

Enhancing Glucose Biosensing with Graphene Oxide and Ferrocene-Modified Linear Poly(ethylenimine)

We designed and optimized a glucose biosensor system based on a screen-printed electrode modified with the NAD-GDH enzyme. To enhance the electroactive surface area and improve the electron transfer efficiency, we introduced graphene oxide (GO) and ferrocene-modified linear poly(ethylenimine) (LPEI-Fc) onto the biosensor surface. This strategic modification exploits the electrostatic interaction between graphene oxide, which possesses a negative charge, and LPEI-Fc, which is positively charged. This interaction results in increased catalytic current during glucose oxidation and helps improve the overall glucose detection sensitivity by amperometry. We integrated the developed glucose sensor into a flow injection (FI) system. This integration facilitates a swift and reproducible detection of glucose, and it also mitigates the risk of contamination during the analyses. The incorporation of an FI system improves the efficiency of the biosensor, ensuring precise and reliable results in a short time. The proposed sensor was operated at a constant applied potential of 0.35 V. After optimizing the system, a linear calibration curve was obtained for the concentration range of 1.0-40 mM (R2 = 0.986). The FI system was successfully applied to determine the glucose content of a commercial sports drink.

Fabrication of a Novel Optical Glucose Biosensor Using Copper(II) Neocuproine as a Chromogenic Oxidant and Glucose Dehydrogenase-Immobilized Magnetite Nanoparticles

This study describes a novel optical glucose biosensor based on a colorimetric reaction between reduced nicotinamide adenine dinucleotide (NADH) and a copper(II) neocuproine complex ([Cu(Nc)2]2+) as a chromogenic oxidant. An enzymatic reaction takes place between glucose and glucose dehydrogenase (GDH)-chitosan (CS) immobilized on silanized magnetite nanoparticles (CS@SiO2@Fe3O4) in the presence of coenzyme NAD+. The oxidation of glucose to gluconolactone via the immobilized enzyme is coupled with the reduction of NAD+ to NADH at the same time. After the separation of GDH-immobilized SiO2@Fe3O4 with a magnet, the enzymatically produced NADH chemically reduces the chromogenic oxidant cupric neocuproine to the cuprous chelate. Thus, the glucose biosensor is fabricated based on the measurement of the absorbance of the formed yellow-orange complex ([Cu(Nc)2]+) at 450 nm. The obtained results show that the colorimetric biosensor has a wide linear response range for glucose, between 1.0 and 150.0 μM under optimized conditions. The limit of detection and limit of quantification were found to be 0.31 and 1.02 μM, respectively. The selectivity properties of the fabricated biosensor were tested with various interfering species. This biosensor was applied to various samples, and the obtained results suggest that the fabricated optical biosensor can be successfully used for the selective and sensitive determination of glucose in real samples.

Visioning synthetic futures for yeast research within the context of current global techno-political trends

Yeast research is entering into a new period of scholarship, with new scientific tools, new questions to ask and new issues to consider. The politics of emerging and critical technology can no longer be separated from the pursuit of basic science in fields, such as synthetic biology and engineering biology. Given the intensifying race for technological leadership, yeast research is likely to attract significant investment from government, and that it offers huge opportunities to the curious minded from a basic research standpoint. This article provides an overview of new directions in yeast research with a focus on Saccharomyces cerevisiae, and places these trends in their geopolitical context. At the highest level, yeast research is situated within the ongoing convergence of the life sciences with the information sciences. This convergent effect is most strongly pronounced in areas of AI-enabled tools for the life sciences, and the creation of synthetic genomes, minimal genomes, pan-genomes, neochromosomes and metagenomes using computer-assisted design tools and methodologies. Synthetic yeast futures encompass basic and applied science questions that will be of intense interest to government and nongovernment funding sources. It is essential for the yeast research community to map and understand the context of their research to ensure their collaborations turn global challenges into research opportunities.

Lignocellulosic biomass valorization via bio-photo/electro hybrid catalytic systems

Lignocellulosic biomass valorization is regarded as a promising approach to alleviate energy crisis and achieve carbon neutrality. Bioactive enzymes have attracted great attention and been commonly applied for biomass valorization owing to their high selectivity and catalytic efficiency under environmentally benign reaction conditions. Same as biocatalysis, photo-/electro-catalysis also happens at mild conditions (i.e., near ambient temperature and pressure). Therefore, the combination of these different catalytic approaches to benefit from their resulting synergy is appealing. In such hybrid systems, harness of renewable energy from the photo-/electro-catalytic compartment can be combined with the unique selectivity of biocatalysts, therefore providing a more sustainable and greener approach to obtain fuels and value-added chemicals from biomass. In this review, we firstly introduce the pros/cons, classifications, and the applications of photo-/electro-enzyme coupled systems. Then we focus on the fundamentals and comprehensive applications of the most representative biomass-active enzymes including lytic polysaccharide monooxygenases (LPMOs), glucose oxidase (GOD)/dehydrogenase (GDH) and lignin peroxidase (LiP), together with other biomass-active enzymes in the photo-/electro- enzyme coupled systems. Finally, we propose current deficiencies and future perspectives of biomass-active enzymes to be applied in the hybrid catalytic systems for global biomass valorization.

Availability of Biomass and Potential of Nanotechnologies for Bioenergy Production in Jordan

Jordan’s energy situation is in a critical state of dependency, with the country relying heavily on imports to satisfy its ever-increasing energy requirements. Renewable energy is a more competitive and consistent source of energy that can supply a large proportion of a country’s energy demand. It is environmentally friendly and minimizes atmospheric pollutant emissions. Thus, bioenergy has the potential to be a crucial alternative energy source in Jordan. Biomass is the principal source of bioenergy; it accounts for approximately 13% of the primary energy demand and is anticipated to supply half of the total primary energy demand by 2050. Nanotechnology has emerged as an important scientific research area with numerous applications, including biofuels. This review summarizes the application of nanoparticles to improve the properties and processes of biofuels. It presents the availability and viability of nanotechnology-supported bioenergy production in Jordan. Jordan generates up to 5.8 million tons of biomass each year and has access to abundant nonedible plant resources (such as Jojoba, Handal, and Jatropha). The theoretical energy potential of waste and residue available in Jordan was also assessed; it was discovered that the 1.28 million tons of dry crop residues (vegetables, fruits, and farming crops) could generate 6.8 PJ of energy per year and that biogas could be generated at a rate of 817 MCM/year

Direct Electrochemistry of Glucose Dehydrogenase-Functionalized Polymers on a Modified Glassy Carbon Electrode and Its Molecular Recognition of Glucose

A glucose biosensor was layer-by-layer assembled on a modified glassy carbon electrode (GCE) from a nanocomposite of NAD(P)⁺-dependent glucose dehydrogenase, aminated polyethylene glycol (mPEG), carboxylic acid-functionalized multi-wall carbon nanotubes (fMWCNTs), and ionic liquid (IL) composite functional polymers. The electrochemical electrode was denoted as NF/IL/GDH/mPEG-fMWCNTs/GCE. The composite polymer membranes were characterized by cyclic voltammetry, ultraviolet-visible spectrophotometry, electrochemical impedance spectroscopy, scanning electron microscopy, and transmission electron microscopy. The cyclic voltammogram of the modified electrode had a pair of well-defined quasi-reversible redox peaks with a formal potential of -61 mV (vs. Ag/AgCl) at a scan rate of 0.05 V s^-1. The heterogeneous electron transfer constant (k_s) of GDH on the composite functional polymer-modified GCE was 6.5 s^-1. The biosensor could sensitively recognize and detect glucose linearly from 0.8 to 100 µM with a detection limit down to 0.46 μM (S/N = 3) and a sensitivity of 29.1 nA μM^-1. The apparent Michaelis-Menten constant (Kmapp) of the modified electrode was 0.21 mM. The constructed electrochemical sensor was compared with the high-performance liquid chromatography method for the determination of glucose in commercially available glucose injections. The results demonstrated that the sensor was highly accurate and could be used for the rapid and quantitative determination of glucose concentration.

Redox Biocatalysis: Quantitative Comparisons of Nicotinamide Cofactor Regeneration Methods

Enzymatic processes, particularly those capable of performing redox reactions, have recently been of growing research interest. Substrate specificity, optimal activity at mild temperatures, high selectivity, and yield are among the desirable characteristics of these oxidoreductase catalyzed reactions. Nicotinamide adenine dinucleotide (phosphate) or NAD(P)H-dependent oxidoreductases have been extensively studied for their potential applications like biosynthesis of chiral organic compounds, construction of biosensors, and pollutant degradation. One of the main challenges associated with making these processes commercially viable is the regeneration of the expensive cofactors required by the enzymes. Numerous efforts have pursued enzymatic regeneration of NAD(P)H by coupling a substrate reduction with a complementary enzyme catalyzed oxidation of a co-substrate. While offering excellent selectivity and high total turnover numbers, such processes involve complicated downstream product separation of a primary product from the coproducts and impurities. Alternative methods comprising chemical, electrochemical, and photochemical regeneration have been developed with the goal of enhanced efficiency and operational simplicity compared to enzymatic regeneration. Despite the goal, however, the literature rarely offers a meaningful comparison of the total turnover numbers for various regeneration methodologies. This comprehensive Review systematically discusses various methods of NAD(P)H cofactor regeneration and quantitatively compares performance across the numerous methods. Further, fundamental barriers to enhanced cofactor regeneration in the various methods are identified, and future opportunities are highlighted for improving the efficiency and sustainability of commercially viable oxidoreductase processes for practical implementation.

Directed evolution engineering to improve activity of glucose dehydrogenase by increasing pocket hydrophobicity

Glucose dehydrogenase (GDH) is a NAD(P)+ dependent oxidoreductase, which is useful in glucose determination kits, glucose biosensors, cofactor regeneration, and biofuel cells. However, the low efficiency of the catalysis hinders the use of GDH in industrial applications. In this study, an analysis of interactions between eight GDH mutants and NADP+ is powered by AlphaFold2 and Discovery Studio 3.0. The docking results showed that more hydrogen bonds formed between mutants, such as P45A and NADP+, which indicated that these mutants had the potential for high catalytic efficiency. Subsequently, we verified all the mutants by site-directed mutagenesis. It was notable that the enzyme activity of mutant P45A was 1829 U/mg, an improvement of 28-fold compared to wild-type GDH. We predicted the hydrophobicity of the protein-ligand complexes, which was confirmed by an 8-anilino-1-naphthalenesulphonic acid fluorescent probe. The following order of increasing hydrophobicity index was deduced: GDH < N46E < F155Y < P45A, which suggested that the enzyme activity of GDH is positively related to its pocket hydrophobicity. Furthermore, P45A still showed better catalytic ability in organic solvents, reaching 692 U/mg in 10% isopropanol, which was 19-fold that of the wild-type GDH. However, its substrate affinity was affected by organic solvents. This study provides a good theoretical foundation for further improving the catalytic efficiency of GDH.

A Universal Multichannel Platform for Assembling Enzyme-Based Boolean Logic Gates

Concatenated enzyme-based Boolean logic gates activated with 5 chemical input signals were analyzed with a smartphone photo camera. Simultaneous detection of 32 input combinations was conveniently performed using enzyme-modified fiberglass sensing spots generating fluorescence with different intensities for the 0 and 1 binary outputs. The developed technology offers an easy readout method for multi-channel logic systems.

Glucose Oxidase, an Enzyme "Ferrari": Its Structure, Function, Production and Properties in the Light of Various Industrial and Biotechnological Applications

Glucose oxidase (GOx) is an important oxidoreductase enzyme with many important roles in biological processes. It is considered an "ideal enzyme" and is often called an oxidase "Ferrari" because of its fast mechanism of action, high stability and specificity. Glucose oxidase catalyzes the oxidation of β-d-glucose to d-glucono-δ-lactone and hydrogen peroxide in the presence of molecular oxygen. d-glucono-δ-lactone is sequentially hydrolyzed by lactonase to d-gluconic acid, and the resulting hydrogen peroxide is hydrolyzed by catalase to oxygen and water. GOx is presently known to be produced only by fungi and insects. The current main industrial producers of glucose oxidase are Aspergillus and Penicillium. An important property of GOx is its antimicrobial effect against various pathogens and its use in many industrial and medical areas. The aim of this review is to summarize the structure, function, production strains and biophysical and biochemical properties of GOx in light of its various industrial, biotechnological and medical applications.

Efficient Asymmetric Synthesis of (S)-N-Boc-3-Hydroxypiperidine by Coexpressing Ketoreductase and Glucose Dehydrogenase

(S)-N-Boc-3-hydroxypiperidine is an important intermediate of the anticancer drug ibrutinib and is mainly synthesized by the asymmetric reduction catalyzed by ketoreductase coupled with glucose dehydrogenase at present. In this study, the coexpression recombinant strains E. coli/pET28-K-rbs-G with single promoter and E. coli/pETDuet-K-G with double promoters were first constructed for the coexpression of ketoreductase and glucose dehydrogenase in the same cell. Then, the catalytic efficiency of E. coli/pET28-K-rbs-G for synthesizing (S)-N-Boc-3-hydroxypiperidine was found to be higher than that of E. coli/pETDuet-K-G due to the more balanced activity ratio and higher catalytic activity. On this basis, the catalytic conditions of E. coli/pET28-K-rbs-G were further optimized, and finally both the conversion of the reaction and the optical purity of the product were higher than 99%. In the end, the cell-free extract was proved to be a better catalyst than the whole cell with the improved catalytic efficiency of different recombinant strains. This study developed a better coexpression strategy for ketoreductase and glucose dehydrogenase by investigating the effect of activity ratios and forms of the biocatalysts on the catalytic efficiency deeply, which provided a research basis for the efficient synthesis of chiral compounds.

Hybrid catalyst cascade for enhanced oxidation of glucose in glucose/air biofuel cell

Redox enzymes are capable of harvesting electrical energy from biofuels in high catalytic activity and under mild condition. However, it is difficult to achieve efficient electron transfer and deep oxidation of biofuels simultaneously in a single-enzyme catalytic system. Herein, we report a hybrid catalyst cascade consisting of an organic oxidation catalyst, 2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO), and an enzyme, glucose oxidase (GOx), for electrochemical oxidation of glucose. It is found that TEMPO is capable of mediating electron transfer between the redox center of GOx and the electrode surface. While glucose can be oxidized into glucuronic acid under neutral conditions. Thus, combining GOx and TEMPO, we are able to achieve 4e- electrooxidation of glucose using the hybrid enzymatic and organic cascade (HEOC) system. When coupled with an air-breathing Pt cathode, the resulting glucose/air biofuel cell using the proposed HEOC anode exhibits a maximum power density of 38.1 μW cm-2 with a short-circuit current of 651.4 μA cm-2, which can be attributed to the enhanced energetic efficiency, enabling TEMPO a promising catalyst for glucose oxidation in bioelectronics applications.

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.

Recent Advances in Enzymatic and Non-Enzymatic Electrochemical Glucose Sensing

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

Development of a Glucose Sensor Based on Glucose Dehydrogenase Using Polydopamine-Functionalized Nanotubes

The electrochemical-based detection of glucose is widely used for diagnostic purposes and is mediated by enzyme-mediated signal transduction mechanisms. For such applications, recent attention has focused on utilizing the oxygen-insensitive glucose dehydrogenase (GDH) enzyme in place of the glucose oxidase (GOx) enzyme, which is sensitive to oxygen levels. Currently used Ru-based redox mediators mainly work with GOx, while Ru(dmo-bpy)2Cl2 has been proposed as a promising mediator that works with GDH. However, there remains an outstanding need to improve Ru(dmo-bpy)2Cl2 attachment to electrode surfaces. Herein, we report the use of polydopamine-functionalized multi-walled carbon nanotubes (PDA-MWCNTs) to effectively attach Ru(dmo-bpy)2Cl2 and GDH onto screen-printed carbon electrodes (SPCEs) without requiring a cross-linker. PDA-MWCNTs were characterized by Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and thermal gravimetric analysis (TGA), while the fabrication and optimization of Ru(dmo-bpy)2Cl2/PDA-MWCNT/SPCEs were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The experimental results demonstrate a wide linear range of glucose-concentration-dependent responses and the multi-potential step (MPS) technique facilitated the selective detection of glucose in the presence of physiologically relevant interfering species, as well as in biological fluids (e.g., serum). The ease of device fabrication and high detection performance demonstrate a viable pathway to develop glucose sensors based on the GDH enzyme and Ru(dmo-bpy)2Cl2 redox mediator and the sensing strategy is potentially extendable to other bioanalytes as well.

From Enzyme Stability to Enzymatic Bioelectrode Stabilization Processes

Bioelectrocatalysis using redox enzymes appears as a sustainable way for biosensing, electricity production, or biosynthesis of fine products. Despite advances in the knowledge of parameters that drive the efficiency of enzymatic electrocatalysis, the weak stability of bioelectrodes prevents large scale development of bioelectrocatalysis. In this review, starting from the understanding of the parameters that drive protein instability, we will discuss the main strategies available to improve all enzyme stability, including use of chemicals, protein engineering and immobilization. Considering in a second step the additional requirements for use of redox enzymes, we will evaluate how far these general strategies can be applied to bioelectrocatalysis.

Pseudomonas fragi/graphene–gold hybrid nanomaterial bioanode based microbial fuel cell

A Pseudomonas fragi (P. fragi) and graphene–gold hybrid nanomaterial included a carbon felt electrode (graphene–Au/CFE) bioanode was developed and optimized.

Display of Microbial Glucose Dehydrogenase and Cholesterol Oxidase on the Yeast Cell Surface for the Detection of Blood Biochemical Parameters

High levels of blood glucose are always associated with numerous complications including cholesterol abnormalities. Therefore, it is important to simultaneously monitor blood glucose and cholesterol levels in patients with diabetes during the management of chronic diseases. In this study, a glucose dehydrogenase from Aspergillus oryzae TI and a cholesterol oxidase from Chromobacterium sp. DS-1 were displayed on the surface of Saccharomyces cerevisiae, respectively, using the yeast surface display system at a high copy number. In addition, two whole-cell biosensors were constructed through the immobilization of the above yeast cells on electrodes, for electrochemical detection of glucose and cholesterol. The assay time was 8.5 s for the glucose biosensors and 30 s for the cholesterol biosensors. Under optimal conditions, the cholesterol biosensor exhibited a linear range from 2 to 6 mmol·L-1. The glucose biosensor responded efficiently to the presence of glucose at a concentration range of 20-600 mg·dL-1 (1.4-33.3 mmol·L-1) and showed excellent anti-xylose interference properties. Both biosensors exhibited good performance at room temperature and remained stable over a three-week storage period.