Poly(neutral red) as a NAD+ reduction catalyst and a NADH oxidation catalyst: Towards the development of a rechargeable biobattery

Harnessing Redox Polymer Dynamics for Enhanced Glucose-Oxygen Coupling in Dual Biosensing and Therapeutic Applications

The burgeoning field of continuous glucose monitoring (CGM) for diabetes management faces significant challenges, particularly in achieving precise and stable biosensor performance under changing environmental conditions such as varying glucose concentrations and O2 levels. To address this, we present a novel biosensor based on the electroless coupling of glucose oxidation catalyzed by flavin-dependent glucose dehydrogenase (FAD-GDH) and O2 reduction catalyzed by bilirubin oxidase (BOD) via a redox polymer, dimethylferrocene-modified linear poly(ethylenimine), FcMe2-LPEI. Initial cyclic voltammetry tests confirm the colocalization of both enzymatic reactions within the potential range of the polymer, indicating an effective electron shuttle mechanism. As a result, we created a hybrid biosensor that operates at open-circuit potential (OCP). It can detect glucose concentrations of up to 100 mM under various O2 conditions, including ambient air. This resulted from optimizing the enzyme ratio to 120 ± 10 mUBOD·UFAD-GDH-1·atmO2-1. This biosensor is highly sensitive, a crucial feature for CGM applications. This distinguishes it from FAD-GDH traditional biosensors, which require a potential to be applied to measure glucose concentrations up to 30 mM. In addition, this biosensor demonstrates the ability to function as a noninvasive, external device that can adapt to changing glucose levels, paving the way for its use in diabetes care and, potentially, personalized healthcare devices. Furthermore, by leveraging the altered metabolic pathways in tumor cells, this system architecture opened up new avenues for targeted glucose scavenging and O2 reduction in cancer therapy.

Advanced Electroanalysis for Electrosynthesis

Electrosynthesis is a popular, environmentally friendly substitute for conventional organic methods. It involves using charge transfer to stimulate chemical reactions through the application of a potential or current between two electrodes. In addition to electrode materials and the type of reactor employed, the strategies for controlling potential and current have an impact on the yields, product distribution, and reaction mechanism. In this Review, recent advances related to electroanalysis applied in electrosynthesis were discussed. The first part of this study acts as a guide that emphasizes the foundations of electrosynthesis. These essentials include instrumentation, electrode selection, cell design, and electrosynthesis methodologies. Then, advances in electroanalytical techniques applied in organic, enzymatic, and microbial electrosynthesis are illustrated with specific cases studied in recent literature. To conclude, a discussion of future possibilities that intend to advance the academic and industrial areas is presented.

Rapid Entrapment of Phenazine Ethosulfate within a Polyelectrolyte Complex on Electrodes for Efficient NAD+ Regeneration in Mediated NAD+-Dependent Bioelectrocatalysis

Over the past two decades, the designs of redox polymers have become critical to the field of mediated bioelectrocatalysis and are used in commercial glucose biosensors, as well as other bioelectrochemical applications (e.g., energy harvesting). These polymers are specifically used to immobilize redox mediators on electrode surfaces, allowing for self-exchange-based conduction of electrons from enzymes far from the electrode to the electrode surface. However, the synthesis of redox polymers is challenging and results in large batch-to-batch variability. Herein, we report a rapid entrapment of mediators for NAD⁺-dependent bioelectrocatalysis within reverse ionically condensed polyelectrolytes. A high ionic strength aqueous solution of oppositely charged polyelectrolytes, composed of cationic polyguanidinium (PG) chloride and anionic sodium hexametaphosphate (P6), undergoes phase inversion into a solid microporous polyelectrolyte complex (PEC) when introduced into a low ionic strength aqueous solution. The ionic strength-triggered phase inversion of PGP6 solutions was investigated as a means to entrap mediators on the surface of electrodes for mediated bioelectrocatalysis. Compared to the traditional cross-linked immobilizations using redox polymers, this phase inversion takes place within seconds and requires up to 60 min for complete stabilization. In this work, redox mediator phenazine ethosulfate (PES) was entrapped within PGP6 on electrode surfaces for nicotinamide adenine dinucleotide (NAD⁺)-dependent bioelectrocatalysis. In the bulk solution, NAD⁺-dependent dehydrogenase enzymes catalyze the oxidation of the substrate while reducing NAD to reduced nicotinamide adenine dinucleotide (NADH). The resulting NADH is reoxidized to NAD⁺ by the entrapped PES that gets reduced on the electrode, completing the NAD⁺-regeneration-based bioelectrocatalysis. To show the use of these new materials in an application, biofuel cells were evaluated using four different anodic enzyme systems (alcohol dehydrogenase, lactate hydrogenase, glycerol dehydrogenase, and glucose dehydrogenase).

Enzymatic Glucose-Based Bio-batteries: Bioenergy to Fuel Next-Generation Devices

This article consists of a review of the main concepts and paradigms established in the field of biological fuel cells or biofuel cells. The aim is to provide an overview of the current panorama, basic concepts, and methodologies used in the field of enzymatic biofuel cells, as well as the applications of these bio-systems in flexible electronics and implantable or portable devices. Finally, the challenges needing to be addressed in the development of biofuel cells capable of supplying power to small size devices with applications in areas related to health and well-being or next-generation portable devices are analyzed. The aim of this study is to contribute to biofuel cell technology development; this is a multidisciplinary topic about which review articles related to different scientific areas, from Materials Science to technology applications, can be found. With this article, the authors intend to reach a wide readership in order to spread biofuel cell technology for different scientific profiles and boost new contributions and developments to overcome future challenges.

Electricity-driven 7α-hydroxylation of a steroid catalyzed by a cytochrome P450 monooxygenase in engineered yeast

Schematic diagram of the cytochrome P450 monooxygenase-catalyzed BES.

Electron Transfer Between Enzymes and Electrodes

Efficient electron transfer between redox enzymes and electrocatalytic surfaces plays a significant role in development of novel energy conversion devices as well as novel reactors for production of commodities and fine chemicals. Major application examples are related to enzymatic fuel cells and electroenzymatic reactors, as well as enzymatic biosensors. The two former applications are still at the level of proof-of-concept, partly due to the low efficiency and obstacles to electron transfer between enzymes and electrodes. This chapter discusses the theoretical backgrounds of enzyme/electrode interactions, including the main mechanisms of electron transfer, as well as thermodynamic and kinetic aspects. Additionally, the main electrochemical methods of study are described for selected examples. Finally, some recent advancements in the preparation of enzyme-modified electrodes as well as electrodes for soluble co-factor regeneration are reviewed. Graphical Abstract.

Conducting polymer and its composite materials based electrochemical sensor for Nicotinamide Adenine Dinucleotide (NADH)

Nicotinamide Adenine Dinucleotide (NADH) is an important coenzyme in the human body that participates in many metabolic reactions. The impact of abnormal concentrations of NADH significantly causes different diseases in human body. Electrochemical detection of NADH using bare electrode is a challenging task especially in the presence of main electroactive interferences such as ascorbic acid (AA), uric acid (UA) and dopamine (DA). Modified electrodes have been widely explored to overcome the problems of poor sensitivity and selectivity occurred from bare electrodes. This review gives an overview on the progress of using conducting polymers, polyelectrolyte and its composites (co-polymer, carbonaceous, metal, metal oxide and clay) based modified electrodes for the sensing of NADH. In addition, developments on the fabrication of numerous conducting polymer composites based modified electrodes are clearly described.

Effect of Aptamer Binding on the Electron-Transfer Properties of Redox Cofactors

In vitro selection or SELEX has allowed for the identification of functional nucleic acids (FNAs) that can potentially mimic and replace protein enzymes. These FNAs likely interact with cofactors, just like enzymes bind cofactors in their active sites. Investigating how FNA binding affects cofactor properties is important for understanding how an active site is formed and for developing useful enzyme mimics. Oxidoreductase enzymes contain cofactors in their active sites that allow the enzymes to do redox chemistry. In certain applications, these redox cofactors act as electron-transfer shuttles that transport electrons between the enzymes' active sites and electrode surfaces. Three redox cofactors commonly found in oxidoreductases are flavin adenine dinucleotide, nicotinamide adenine dinucleotide (NAD(+)), and pyrroloquinoline quinone (PQQ). We are interested in investigating how DNA aptamers that bind these cofactors influence the cofactors' redox abilities and if these aptamer-cofactor complexes could serve as redox catalysts. We employed cyclic voltammetry and amperometry to study the electrochemical properties of NAD(+) and PQQ when bound to DNA aptamers. Our results suggest that the aptamers provide a stable environment for the cofactor to participate in redox reactions, although enhanced redox activity was not observed. This work provides a foundation for the development of new FNAs capable of redox activity.

Enzymatic AND logic gate with sigmoid response induced by photochemically controlled oxidation of the output

We report a study of a system which involves an enzymatic cascade realizing an AND logic gate, with an added photochemical processing of the output, allowing the gate's response to be made sigmoid in both inputs. New functional forms are developed for quantifying the kinetics of such systems, specifically designed to model their response in terms of signal and information processing. These theoretical expressions are tested for the studied system, which also allows us to consider aspects of biochemical information processing such as noise transmission properties and control of timing of the chemical and physical steps.

Sol-gel Approaches for Elaboration of Polyol Dehydrogenase-Based Bioelectrodes

This review describes the input of sol-gel chemistry to the immobilization of polyol dehydrogenases on electrodes, for applications in bioelectrocatalysis. The polyol dehydrogenases are described and their application for biosensing, biofuel cell and electrosynthesis are briefly discussed. The immobilization of proteins via sol-gel approaches is described, including a discussion on the difficulty to maintain the activity of proteins in a silica matrix and the strategies developed to offer a proper environment to the proteins by developing optimal organic-inorganic hybrid materials. Finally, the co-immobilization of the NAD + co-factor and of mediators for the elaboration of reagentless devices is presented, based on published and original data. All-in-all, sol-gel approaches appear to be a very promising for development of original electrochemical applications involving dehydrogenases in near future.

In situ regeneration of NADH via lipoamide dehydrogenase-catalyzed electron transfer reaction evidenced by spectroelectrochemistry

NAD/NADH is a coenzyme found in all living cells, carrying electrons from one reaction to another. We report on characterizations of in situ regeneration of NADH via lipoamide dehydrogenase (LD)-catalyzed electron transfer reaction to regenerate NADH using UV-vis spectroelectrochemistry. The Michaelis-Menten constant (K(m)) and maximum velocity (V(max)) of NADH regeneration were measured as 0.80±0.15 mM and 1.91±0.09 μM s(-1) in a 1-mm thin-layer spectroelectrochemical cell using gold gauze as the working electrode at the applied potential -0.75 V (vs. Ag/AgCl). The electrocatalytic reduction of the NAD system was further coupled with the enzymatic conversion of pyruvate to lactate by lactate dehydrogenase to examine the coenzymatic activity of the regenerated NADH. Although the reproducible electrocatalytic reduction of NAD into NADH is known to be difficult compared to the electrocatalytic oxidation of NADH, our spectroelectrochemical results indicate that the in situ regeneration of NADH via LD-catalyzed electron transfer reaction is fast and sustainable and can be potentially applied to many NAD/NADH-dependent enzyme systems.

Immobilized redox mediators for electrochemical NAD(P)+ regeneration

The applicability of dissolved redox mediators for NAD(P)(+) regeneration has been demonstrated several times. Nevertheless, the use of mediators in solutions for sensor applications is not a very convenient strategy since the analysis is not reagentless and long stabilization times occur. The most important drawbacks of dissolved mediators in biocatalytic applications are interferences during product purification, limited reusability of the mediators, and their cost-intensive elimination from wastewater. Therefore, the use of immobilized mediators has both economic and ecological advantages. This work critically reviews the current state-of-art of immobilized redox mediators for electrochemical NAD(P)(+) regeneration. Various surface modification techniques, such as adsorption polymerization and covalent linkage, as well as the corresponding NAD(P)(+) regeneration rates and the operational stability of the immobilized mediator films, will be discussed. By comparison with other existing regeneration systems, the technical potential and future perspectives of biocatalytic redox reactions based on electrochemically fed immobilized mediators will be assessed.

Enzymatic biofuel cells utilizing a biomimetic cofactor

The performance of immobilized enzyme systems is often limited by cofactor diffusion and regeneration. Here, we demonstrate an engineered enzyme capable of utilizing the minimal cofactor nicotinamide mononucleotide (NMN(+)) to address these limitations. Significant gains in performance are observed with NMN(+) in immobilized systems, despite a decreased turnover rate with the minimal cofactor.

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.