Direct Electron Transfer of Cellobiose Dehydrogenase on Positively Charged Polyethyleneimine Gold Nanoparticles

The application of bacteria-derived dehydrogenases and oxidases in the synthesis of gold nanoparticles

In this work the green synthesis of gold nanoparticles (Au-NPs) using the oxidoreductive enzymes Myriococcum thermophilum cellobiose dehydrogenase (Mt CDH), Glomerella cingulata glucose dehydrogenase (Gc GDH), and Aspergillus niger glucose oxidase (An GOX)) as bioreductants was investigated. The influence of reaction conditions on the synthesis of Au-NPs was examined and optimised. The reaction kinetics and the influence of Au ions on the reaction rate were determined. Based on the kinetic study, the mechanism of Au-NP synthesis was proposed. The Au-NPs were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). The surface plasmon resonance (SPR) absorption peaks of the Au-NPs synthesised with Mt CDH and Gc GDH were observed at 535 nm, indicating an average size of around 50 nm. According to the image analysis performed on a TEM micrograph, the Au-NPs synthesized with Gc GDH have a spherical shape with an average size of 2.83 and 6.63 nm after 24 and 48 h of the reaction, respectively. KEY POINTS: • The Au NPs were synthesised by the action of enzymes CDH and GDH. • The synthesis of Au-NPs by CDH is related to the oxidation of cellobiose. • The synthesis of Au-NPs by GDH was not driven by the reaction kinetic.

Direct Electron Transfer-Type Oxidoreductases for Biomedical Applications

Among the various types of enzyme-based biosensors, sensors utilizing enzymes capable of direct electron transfer (DET) are recognized as the most ideal. However, only a limited number of redox enzymes are capable of DET with electrodes, that is, dehydrogenases harboring a subunit or domain that functions specifically to accept electrons from the redox cofactor of the catalytic site and transfer the electrons to the external electron acceptor. Such subunits or domains act as built-in mediators for electron transfer between enzymes and electrodes; consequently, such enzymes enable direct electron transfer to electrodes and are designated as DET-type enzymes. DET-type enzymes fall into several categories, including redox cofactors of catalytic reactions, built-in mediators for DET with electrodes and by their protein hierarchic structures, DET-type oxidoreductases with oligomeric structures harboring electron transfer subunits, and monomeric DET-type oxidoreductases harboring electron transfer domains. In this review, we cover the science of DET-type oxidoreductases and their biomedical applications. First, we introduce the structural biology and current understanding of DET-type enzyme reactions. Next, we describe recent technological developments based on DET-type enzymes for biomedical applications, such as biosensors and biochemical energy harvesting for self-powered medical devices. Finally, after discussing how to further engineer and create DET-type enzymes, we address the future prospects for DET-type enzymes in biomedical engineering.

Conductive Polymers and Their Nanocomposites: Application Features in Biosensors and Biofuel Cells

Conductive polymers and their composites are excellent materials for coupling biological materials and electrodes in bioelectrochemical systems. It is assumed that their relevance and introduction to the field of bioelectrochemical devices will only grow due to their tunable conductivity, easy modification, and biocompatibility. This review analyzes the main trends and trends in the development of the methodology for the application of conductive polymers and their use in biosensors and biofuel elements, as well as describes their future prospects. Approaches to the synthesis of such materials and the peculiarities of obtaining their nanocomposites are presented. Special emphasis is placed on the features of the interfaces of such materials with biological objects.

Recent Advances in Applications of Oxidases and Peroxidases Polymer-Based Enzyme Biocatalysts in Sensing and Wastewater Treatment: A Review

Oxidase and peroxidase enzymes have attracted attention in various biotechnological industries due to their ease of synthesis, wide range of applications, and operation under mild conditions. Their applicability, however, is limited by their poor stability in harsher conditions and their non-reusability. As a result, several approaches such as enzyme engineering, medium engineering, and enzyme immobilization have been used to improve the enzyme properties. Several materials have been used as supports for these enzymes to increase their stability and reusability. This review focusses on the immobilization of oxidase and peroxidase enzymes on metal and metal oxide nanoparticle-polymer composite supports and the different methods used to achieve the immobilization. The application of the enzyme-metal/metal oxide-polymer biocatalysts in biosensing of hydrogen peroxide, glucose, pesticides, and herbicides as well as blood components such as cholesterol, urea, dopamine, and xanthine have been extensively reviewed. The application of the biocatalysts in wastewater treatment through degradation of dyes, pesticides, and other organic compounds has also been discussed.

Nanomaterials in bioelectrochemical devices: on applications enhancing their positive effect

Electrochemical biosensors and biofuel cells are finding an ever-increasing practical application due to several advantages. Biosensors are miniature measuring devices, which can be used for on-the-spot analyses, with small assay times and sample volumes. Biofuel cells have dual benefits of environmental cleanup and electric energy generation. Application of nanomaterials in biosensor and biofuel-cell devices increases their functioning efficiency and expands spheres of use. This review discusses the potential of nanomaterials in improving the basic parameters of bioelectrochemical systems, including the sensitivity increase, detection lower-limit decrease, detection-range change, lifetime increase, substrate-specificity control. In most cases, the consideration of the role of nanomaterials links a certain type of nanomaterial with its effect on the bioelectrochemical device upon the whole. The review aims at assessing the effects of nanomaterials on particular analytical parameters of a biosensor/biofuel-cell bioelectrochemical device.

Amperometric Biosensors Based on Direct Electron Transfer Enzymes

The accurate determination of analyte concentrations with selective, fast, and robust methods is the key for process control, product analysis, environmental compliance, and medical applications. Enzyme-based biosensors meet these requirements to a high degree and can be operated with simple, cost efficient, and easy to use devices. This review focuses on enzymes capable of direct electron transfer (DET) to electrodes and also the electrode materials which can enable or enhance the DET type bioelectrocatalysis. It presents amperometric biosensors for the quantification of important medical, technical, and environmental analytes and it carves out the requirements for enzymes and electrode materials in DET-based third generation biosensors. This review critically surveys enzymes and biosensors for which DET has been reported. Single- or multi-cofactor enzymes featuring copper centers, hemes, FAD, FMN, or PQQ as prosthetic groups as well as fusion enzymes are presented. Nanomaterials, nanostructured electrodes, chemical surface modifications, and protein immobilization strategies are reviewed for their ability to support direct electrochemistry of enzymes. The combination of both biosensor elements-enzymes and electrodes-is evaluated by comparison of substrate specificity, current density, sensitivity, and the range of detection.

Recent Advances in the Direct Electron Transfer-Enabled Enzymatic Fuel Cells

Direct electron transfer (DET), which requires no mediator to shuttle electrons from enzyme active site to the electrode surface, minimizes complexity caused by the mediator and can further enable miniaturization for biocompatible and implantable devices. However, because the redox cofactors are typically deeply embedded in the protein matrix of the enzymes, electrons generated from oxidation reaction cannot easily transfer to the electrode surface. In this review, methods to improve the DET rate for enhancement of enzymatic fuel cell performances are summarized, with a focus on the more recent works (past 10 years). Finally, progress on the application of DET-enabled EFC to some biomedical and implantable devices are reported.

Direct Electrochemical Enzyme Electron Transfer on Electrodes Modified by Self-Assembled Molecular Monolayers

Self-assembled molecular monolayers (SAMs) have long been recognized as crucial “bridges” between redox enzymes and solid electrode surfaces, on which the enzymes undergo direct electron transfer (DET)—for example, in enzymatic biofuel cells (EBFCs) and biosensors. SAMs possess a wide range of terminal groups that enable productive enzyme adsorption and fine-tuning in favorable orientations on the electrode. The tunneling distance and SAM chain length, and the contacting terminal SAM groups, are the most significant controlling factors in DET-type bioelectrocatalysis. In particular, SAM-modified nanostructured electrode materials have recently been extensively explored to improve the catalytic activity and stability of redox proteins immobilized on electrochemical surfaces. In this report, we present an overview of recent investigations of electrochemical enzyme DET processes on SAMs with a focus on single-crystal and nanoporous gold electrodes. Specifically, we consider the preparation and characterization methods of SAMs, as well as SAM applications in promoting interfacial electrochemical electron transfer of redox proteins and enzymes. The strategic selection of SAMs to accord with the properties of the core redox protein/enzymes is also highlighted.

Cellobiose dehydrogenase: Bioelectrochemical insights and applications

Cellobiose dehydrogenase (CDH) is a flavocytochrome with a history of bioelectrochemical research dating back to 1992. During the years, it has been shown to be capable of mediated electron transfer (MET) and direct electron transfer (DET) to a variety of electrodes. This versatility of CDH originates from the separation of the catalytic flavodehydrogenase domain and the electron transferring cytochrome domain. This uncoupling of the catalytic reaction from the electron transfer process allows the application of CDH on many different electrode materials and surfaces, where it shows robust DET. Recent X-ray diffraction and small angle scattering studies provided insights into the structure of CDH and its domain mobility, which can change between a closed-state and an open-state conformation. This structural information verifies the electron transfer mechanism of CDH that was initially established by bioelectrochemical methods. A combination of DET and MET experiments has been used to investigate the catalytic mechanism and the electron transfer process of CDH and to deduce a protein structure comprising of mobile domains. Even more, electrochemical methods have been used to study the redox potentials of the FAD and the haem b cofactors of CDH or the electron transfer rates. These electrochemical experiments, their results and the application of the characterised CDHs in biosensors, biofuel cells and biosupercapacitors are combined with biochemical and structural data to provide a thorough overview on CDH as versatile bioelectrocatalyst.

Direct Electron Transfer of Enzymes Facilitated by Cytochromes

The direct electron transfer (DET) of enzymes has been utilized to develop biosensors and enzymatic biofuel cells on micro- and nanostructured electrodes. Whereas some enzymes exhibit direct electron transfer between their active-site cofactor and an electrode, other oxidoreductases depend on acquired cytochrome domains or cytochrome subunits as built-in redox mediators. The physiological function of these cytochromes is to transfer electrons between the active-site cofactor and a redox partner protein. The exchange of the natural electron acceptor/donor by an electrode has been demonstrated for several cytochrome carrying oxidoreductases. These multi-cofactor enzymes have been applied in third generation biosensors to detect glucose, lactate, and other analytes. This review investigates and classifies oxidoreductases with a cytochrome domain, enzyme complexes with a cytochrome subunit, and covers designed cytochrome fusion enzymes. The structurally and electrochemically best characterized proponents from each enzyme class carrying a cytochrome, that is, flavoenzymes, quinoenzymes, molybdenum-cofactor enzymes, iron-sulfur cluster enzymes, and multi-haem enzymes, are featured, and their biochemical, kinetic, and electrochemical properties are compared. The cytochromes molecular and functional properties as well as their contribution to the interdomain electron transfer (IET, between active-site and cytochrome) and DET (between cytochrome and electrode) with regard to the achieved current density is discussed. Protein design strategies for cytochrome-fused enzymes are reviewed and the limiting factors as well as strategies to overcome them are outlined.

Direct Electron Transfer of Dehydrogenases for Development of 3rd Generation Biosensors and Enzymatic Fuel Cells

Dehydrogenase based bioelectrocatalysis has been increasingly exploited in recent years in order to develop new bioelectrochemical devices, such as biosensors and biofuel cells, with improved performances. In some cases, dehydrogeases are able to directly exchange electrons with an appropriately designed electrode surface, without the need for an added redox mediator, allowing bioelectrocatalysis based on a direct electron transfer process. In this review we briefly describe the electron transfer mechanism of dehydrogenase enzymes and some of the characteristics required for bioelectrocatalysis reactions via a direct electron transfer mechanism. Special attention is given to cellobiose dehydrogenase and fructose dehydrogenase, which showed efficient direct electron transfer reactions. An overview of the most recent biosensors and biofuel cells based on the two dehydrogenases will be presented. The various strategies to prepare modified electrodes in order to improve the electron transfer properties of the device will be carefully investigated and all analytical parameters will be presented, discussed and compared.

Fuel-independent and membrane-less self-charging biosupercapacitor

A fuel-independent self-charging biosupercapacitor consisting of an enzymatic biocathode and a bioelectrode employing supercapacitive features of immobilized myoglobin is described.

A Third Generation Glucose Biosensor Based on Cellobiose Dehydrogenase Immobilized on a Glassy Carbon Electrode Decorated with Electrodeposited Gold Nanoparticles: Characterization and Application in Human Saliva

Efficient direct electron transfer (DET) between a cellobiose dehydrogenase mutant from Corynascus thermophilus (CtCDH C291Y) and a novel glassy carbon (GC)-modified electrode, obtained by direct electrodeposition of gold nanoparticles (AuNPs) was realized. The electrode was further modified with a mixed self-assembled monolayer of 4-aminothiophenol (4-APh) and 4-mercaptobenzoic acid (4-MBA), by using glutaraldehyde (GA) as cross-linking agent. The CtCDH C291Y/GA/4-APh,4-MBA/AuNPs/GC platform showed an apparent heterogeneous electron transfer rate constant (ks) of 19.4 ± 0.6 s-1, with an enhanced theoretical and real enzyme surface coverage (Γtheor and Γreal) of 5287 ± 152 pmol cm-2 and 27 ± 2 pmol cm-2, respectively. The modified electrode was successively used as glucose biosensor exhibiting a detection limit of 6.2 μM, an extended linear range from 0.02 to 30 mM, a sensitivity of 3.1 ± 0.1 μA mM-1 cm-2 (R2 = 0.995), excellent stability and good selectivity. These performances compared favourably with other glucose biosensors reported in the literature. Finally, the biosensor was tested to quantify the glucose content in human saliva samples with successful results in terms of both recovery and correlation with glucose blood levels, allowing further considerations on the development of non-invasive glucose monitoring devices.