Bimolecular Rate Constants for FAD-Dependent Glucose Dehydrogenase from Aspergillus terreus and Organic Electron Acceptors

Insights into carbon nanotube-assisted electro-oxidation of polycyclic aromatic hydrocarbons for mediated bioelectrocatalysis

A series of polycyclic aromatics, naphthalene, phenanthrene, perylene, pyrene, 1-pyrenebutyric acid N-hydroxysuccinimide ester (pyrene NHS) and coronene, were immobilized via π stacking on carbon nanotube (CNT) electrodes and electro-oxidized in aqueous solutions. The obtained quinones were characterized and evaluated for the mediated electron transfer with FAD dependent glucose dehydrogenase during catalytic glucose oxidation.

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.

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.

Disposable electrochemical glucose sensor based on water-soluble quinone-based mediators with flavin adenine dinucleotide-dependent glucose dehydrogenase

Glucose level measurement is essential for the point-of-care diagnosis, primarily for persons with diabetes. A disposable electrochemical glucose sensor is constructed using flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) and redox mediator for electron transfer from the enzyme to the electrode surface. Ideally, a suitable mediator should have high water solubility, high kinetic constant, high stability, and redox potential between -0.2 and 0.1 V vs. Ag|AgCl|sat. KCl. We designed and synthesized two new quinone-based water-soluble mediators: quinoline-5,8-dione (QD) and isoquinoline-5,8-dione (IQD). The formal potentials for both QD and IQD at pH 7.0 were -0.07 V vs. Ag|AgCl|sat. KCl. The logarithms of the electron exchange rate constants (k₂/(M^-1 s^-1)) between QD/IQD and FAD-GDH were 7.7 ± 0.1 and 7.4 ± 0.1 for QD and IQD, respectively, which are the highest value among the water-soluble mediators for FAD-GDH reported to date. Disposable amperometric glucose sensors were fabricated by dropping FAD-GDH and QD or IQD onto a test strip. The sensor achieved a linear response up to glucose concentrations of 55.5 mM. The linear response was obtained even when the mediator loading was low (0.5 nmol/strip); loading was only 0.2 mol% of glucose. The results proved that the response current was primarily controlled by glucose diffusion. In addition, the sensor using QD exhibited high stability over 3 months at room temperature.

Solid-phase recombinase polymerase amplification using an extremely low concentration of a solution primer for sensitive electrochemical detection of hepatitis B viral DNA

Recombinase polymerase amplification (RPA) is considered one of the best amplification methods for realizing a miniaturized diagnostic instrument; however, it is notably challenging to obtain low detection limits in solid-phase RPA. To overcome these difficulties, we combined solid-phase RPA with electrochemical detection and used a new concentration combination of three primers (surface-bound forward primer, solution reverse primer, and an extremely low concentration of solution forward primer). When solid-phase RPA was performed on an indium tin oxide (ITO) electrode modified with a surface-bound forward primer in a solution containing a biotin-terminated solution reverse primer, an extremely low concentration of a solution forward primer, and a template DNA or genomic DNA for a target gene of hepatitis B virus (HBV), amplification occurred mainly in solution until all the solution forward primers were consumed. Subsequently, DNA amplicons produced in solution participated in solid-phase amplification involving surface-bound forward primer and solution reverse primer. Afterward, neutravidin-conjugated DT-diaphorase (DT-D) was attached to a biotin-terminated DNA amplicon on the ITO electrode. Finally, chronocoulometric charges were measured using electrochemical-enzymatic redox cycling involving the ITO electrode, 1,4-naphthoquinone, DT-D, and reduced β-nicotinamide adenine dinucleotide. The detection limit for HBV was measured using microfabricated electrodes and was found to be approximately 0.1 fM. This proposed method demonstrated better amplification efficiency for HBV genomic DNA than solid-phase RPA without using additional solution primer and asymmetric solid-phase RPA.

Employment of 1-Methoxy-5-Ethyl Phenazinium Ethyl Sulfate as a Stable Electron Mediator in Flavin Oxidoreductases-Based Sensors

In this paper, a novel electron mediator, 1-methoxy-5-ethyl phenazinium ethyl sulfate (mPES), was introduced as a versatile mediator for disposable enzyme sensor strips, employing representative flavin oxidoreductases, lactate oxidase (LOx), glucose dehydrogenase (GDH), and fructosyl peptide oxidase (FPOx). A disposable lactate enzyme sensor with oxygen insensitive Aerococcus viridans-derived engineered LOx (AvLOx), with A96L mutant as the enzyme, was constructed. The constructed lactate sensor exhibited a high sensitivity (0.73 ± 0.12 μA/mM) and wide linear range (0–50 mM lactate), showings that mPES functions as an effective mediator for AvLOx. Employing mPES as mediator allowed this amperometric lactate sensor to be operated at a relatively low potential of +0.2 V to 0 V vs. Ag/AgCl, thus avoiding interference from uric acid and acetaminophen. The lactate sensors were adequately stable for at least 48 days of storage at 25 °C. These results indicated that mPES can be replaced with 1-methoxy-5-methyl phenazinium methyl sulfate (mPMS), which we previously reported as the best mediator for AvLOx-based lactate sensors. Furthermore, this study revealed that mPES can be used as an effective electron mediator for the enzyme sensors employing representative flavin oxidoreductases, GDH-based glucose sensors, and FPOx-based hemoglobin A1c (HbA1c) sensors.

Mediated electrochemical oxidation of glucose via poly(methylene green) grafted on the carbon surface catalyzed by flavin adenine dinucleotide-dependent glucose dehydrogenase

Electrochemically polymerized phenothiazines (thionine, methylene green, methylene blue, and toluidine blue) on carbon electrodes were investigated as electron transfer mediators of glucose oxidation by flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) for biosensor and biofuel cell applications. Among the tested polyphenothiazines grafted on a glassy carbon electrode, clear redox-mediating activity was observed for poly(methylene green), and the catalytic oxidation current depended on the concentrations of glucose and enzymes and the amount of polymer deposited on the electrode surface. The poly(methylene green)-grafted porous carbon electrodes showed 3 mA cm-2 of glucose oxidation current catalyzed by FAD-GDH.

Surveillance Accuracy of Smartphone-Dependent Glucose Meters in the Measurement of Plasma Glucose

BACKGROUND

Along with stand-alone glucose monitors, smartphone-dependent glucose meters (SDGM) are available for self-monitoring of blood glucose (SMBG). These display-less devices, connected to a smartphone, measure glucose and display report on a smartphone screen, which can be easily shared with doctors.

AIM

The aim of this study was to check the accuracy of the available SDGMs in relation to the laboratory reference method.

MATERIALS AND METHODS

Two available SDGMs: BeatO™ and GlucoMe™ were tested. A total of 104 venous blood samples were tested for glucose in SDGMs and by the reference method. The accuracy of the report was checked by the International Standards Organization (ISO), American Diabetes Association (ADA), and Clinical Laboratory Improvement Amendments (CLIA) criteria. Clarke error grid analysis (CEGA) was carried out to find the suitability of SDGM in clinical usage.

RESULTS

Mean plasma glucose (n = 104) level from laboratory report was 106.48 ± 44.58 mg/dL, that from BeatO™ was 105.78 ± 52.6, and GlucoMe™ was 99.72 ± 51.22. The accuracy was lower than that recommended by ISO 2013 (29.8% and 30.77% error in BeatO™ and GlucoMe™, respectively), ADA (63.46% and 74% error in BeatO™ and GlucoMe™, respectively), and CLIA (42.31% and 46.15% error in BeatO™ and GlucoMe™, respectively) criteria. According to CEGA, BeatO™ and GlucoMe™ can guide correct treatment in diabetes mellitus patients for 74% and 71% of measurement, respectively.

CONCLUSION

The accuracy of both the SDGMs was lower than that suggested by ISO, ADA, and CLIA criteria. The result of this study would help patients and doctors in informed choice for the procurement of glucose monitors.

Consecutive Marcus Electron and Proton Transfer in Heme Peroxidase Compound II-Catalysed Oxidation Revealed by Arrhenius Plots

Electron and proton transfer reactions in enzymes are enigmatic and have attracted a great deal of theoretical, experimental, and practical attention. The oxidoreductases provide model systems for testing theoretical predictions, applying experimental techniques to gain insight into catalytic mechanisms, and creating industrially important bio(electro)conversion processes. Most previous and ongoing research on enzymatic electron transfer has exploited a theoretically and practically sound but limited approach that uses a series of structurally similar (“homologous”) substrates, measures reaction rate constants and Gibbs free energies of reactions, and analyses trends predicted by electron transfer theory. This approach, proposed half a century ago, is based on a hitherto unproved hypothesis that pre-exponential factors of rate constants are similar for homologous substrates. Here, we propose a novel approach to investigating electron and proton transfer catalysed by oxidoreductases. We demonstrate the validity of this new approach for elucidating the kinetics of oxidation of “non-homologous” substrates catalysed by compound II of Coprinopsis cinerea and Armoracia rusticana peroxidases. This study – using the Marcus theory – demonstrates that reactions are not only limited by electron transfer, but a proton is transferred after the electron transfer event and thus both events control the reaction rate of peroxidase-catalysed oxidation of substrates.

From fundamentals to applications of bioelectrocatalysis: bioelectrocatalytic reactions of FAD-dependent glucose dehydrogenase and bilirubin oxidase

In this review, I present the main highlights of my works in the development of bioelectrocatalysis, which can be used in widespread applications, particularly for the design of biosensor and biofuel cells. In particular, I focus on research progress made in two key bioelectrocatalytic reactions: glucose oxidation by flavin adenine dinucleotide-dependent glucose dehydrogenase and oxygen reduction by bilirubin oxidase. I demonstrate the fundamental principles of bioelectrocatalysis and the requirements for enhancing the catalytic performance, including the choice of a mediator of redox reactions, immobilization, and electrode materials. These methods can allow for achieving control of the bioelectrocatalytic reaction, thereby overcoming obstacles toward their industrial applications.

Tuning the redox potential of vitamin K3 derivatives by oxidative functionalization using a Ag(i)/GO catalyst

We propose herein initial results to develop optimum redox mediators by the combination of computational simulation and catalytic functionalization of the core structure of vitamin K₃. We aim to correlate the calculated energy value of the LUMO of different vitamin K₃ derivatives with their actual redox potential. For this, we optimized the catalytic alkylation of 1,4-naphthoquinones with a designed Ag(i)/GO catalyst and synthesized a series of molecules.

Mediator Preference of Two Different FAD-Dependent Glucose Dehydrogenases Employed in Disposable Enzyme Glucose Sensors

Most commercially available electrochemical enzyme sensor strips for the measurement of blood glucose use an artificial electron mediator to transfer electrons from the active side of the enzyme to the electrode. One mediator recently gaining attention for commercial sensor strips is hexaammineruthenium(III) chloride. In this study, we investigate and compare the preference of enzyme electrodes with two different FAD-dependent glucose dehydrogenases (FADGDHs) for the mediators hexaammineruthenium(III) chloride, potassium ferricyanide (the most common mediator in commercial sensor strips), and methoxy phenazine methosulfate (mPMS). One FADGDH is a monomeric fungal enzyme, and the other a hetero-trimeric bacterial enzyme. With the latter, which contains a heme-subunit facilitating the electron transfer, similar response currents are obtained with hexaammineruthenium(III), ferricyanide, and mPMS (6.8 µA, 7.5 µA, and 6.4 µA, respectively, for 10 mM glucose). With the fungal FADGDH, similar response currents are obtained with the negatively charged ferricyanide and the uncharged mPMS (5.9 µA and 6.7 µA, respectively, for 10 mM glucose), however, no response current is obtained with hexaammineruthenium(III), which has a strong positive charge. These results show that access of even very small mediators with strong charges to a buried active center can be almost completely blocked by the protein.