Significant enhancement of direct electric communication across enzyme-electrode interface via nano-patterning of synthetic glucose dehydrogenase on spatially tunable gold nanoparticle (AuNP)-modified electrode

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.

Novel enzymatic graphene oxide based biosensor for the detection of glutathione in biological body fluids

In this work, we report a novel enzymatic biosensor based on glutathione peroxidase (GSH-Px), graphene oxide (GO) and nafion for the electrochemical sensing of glutathione (GSH) in body fluids. GSH-Px was immobilized covalently via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) onto modified glassy carbon electrode (GCE) decorated with GO and nafion and successfully used for sensing of GSH in the presence of H₂O₂ as catalyst with Michaelis-Menten constant about 0.131 mmol/L. The active surface are of GCE improve from 0.183 cm² to 0.225 cm² after modification with GO. The introduced biosensor (GSH-Px/GO/nafion/GCE) was used for monitoring of GSH over the range 0.003-370.0 μM, with a detection limit of 1.5 nM using differential pulse voltammetric (DPV) method. The GSH-Px/GO/nafion/GCE was successfully applied to the determination of GSH in real samples.

Peptide sequence-driven direct electron transfer properties and binding behaviors of gold-binding peptide-fused glucose dehydrogenase on electrode

Oriented enzyme immobilization on electrodes is crucial for interfacial electrical coupling of direct electron transfer (DET)-based enzyme-electrode systems. As inorganic-binding peptides are introduced as molecular binders and enzyme-orienting agents, inorganic-binding peptide-fused enzymes should be designed and constructed to achieve efficient DET. In this study, it is aimed to compare the effects of various gold-binding peptides (GBPs) fused to enzymes on electrocatalytic activity, bioactivity, and material-binding behaviors. Here, GBPs with identical gold-binding properties but different amino acid sequences were fused to the FAD-dependent glucose dehydrogenase gamma-alpha complex (GDHγα) to generate four GDHγα variants. The structural, biochemical, mechanical, and bioelectrochemical properties of these GDHγα variants immobilized on electrode were determined by their fused GBPs. Our results confirmed that the GBP type is vital in the design, construction, and optimization of GBP-fused enzyme-modified electrodes for facile interfacial DET and practical DET-based enzyme-electrode systems.

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The four GBP sequences are genetically fused to catalytic subunit of GDHγα complex

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The cofactor-surface interface was investigated with 3D models of fusion enzymes

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The four systems exhibit diverse electrochemical results depending on GBP type

Biosensing and electrochemical properties of flavin adenine dinucleotide (FAD)-Dependent glucose dehydrogenase (GDH) fused to a gold binding peptide

In the present work, direct electron transfer (DET) based biosensing system for the determination of glucose has been fabricated by utilizing gold binding peptide (GBP) fused flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) from Burkholderia cepacia. The GBP fused FAD-GDH was immobilized on the working electrode surface of screen-printed electrode (SPE) which consists of gold working electrode, a silver pseudo-reference electrode and a platinum counter electrode, to develop the biosensing system with compact design and favorable sensing ability. The bioelectrochemical and mechanical properties of GBP fused FAD-GDH (GDH-GBP) immobilized SPE (GDH-GBP/Au) were investigated. Here, the binding affinity of GDH-GBP on Au surface, was highly increased after fusion of gold binding peptide and its uniform monolayer was formed on Au surface. In the cyclic voltammetry (CV), GDH-GBP/Au displayed significantly high oxidative peak currents corresponding to glucose oxidation which is almost c.a. 10-fold enhanced value compared with that from native GDH immobilized SPE (GDH/Au). As well, GDH-GBP/Au has shown 92.37% of current retention after successive potential scans. In the chronoamperometry, its steady-state catalytic current was monitored in various conditions. The dynamic range of GDH-GBP/Au was shown to be 3-30 mM at 30 °C and exhibits high selectivity toward glucose in whole human blood. Additionally, temperature dependency of GDH-GBP/Au on DET capability was also investigated at 30-70 °C. Considering this efficient and stable glucose sensing with simple and easy sensor fabrication, GDH-GBP based sensing platform can provide new insight for future biosensor in research fields that rely on DET.

Nanosecond Laser-Fabricated Monolayer of Gold Nanoparticles on ITO for Bioelectrocatalysis

Redox enzymes can be envisioned as biocatalysts in various electrocatalytic-based devices. Among factors that play roles in bioelectrochemistry limitations, the effect of enzyme-enzyme neighboring interaction on electrocatalysis has rarely been investigated, although critical in vivo. We report in this work an in-depth study of gold nanoparticles prepared by laser ablation in the ultimate goal of determining the relationship between activity and enzyme density on electrodes. Nanosecond laser interaction with nanometric gold films deposited on indium tin oxide support was used to generate in situ gold nanoparticles (AuNPs) free from any stabilizers. A comprehensive analysis of AuNP size and coverage, as well as total geometric surface vs. electroactive surface is provided as a function of the thickness of the treated gold layer. Using microscopy and electrochemistry, the long-term stability of AuNP-based electrodes in the atmosphere and in the electrolyte is demonstrated. AuNPs formed by laser treatment are then modified by thiol chemistry and their electrochemical behavior is tested with a redox probe. Finally, enzyme adsorption and bioelectrocatalysis are evaluated in the case of two enzymes, i.e., the Myrothecium verrucaria bilirubin oxidase and the Thermus thermophilus laccase. Behaving differently on charged surfaces, they allow demonstrating the validity of laser treated AuNPs for bioelectrocatalysis.

Dissolved carbon monoxide concentration monitoring platform based on direct electrical connection of CO dehydrogenase with electrically accessible surface structure

CO dehydrogenase (CODH) employed in a dissolved CO biosensor development study harbors a solvent-exposed cofactor capable of DET to electrode. Here, CODH was immobilized on arrays of AuNPs of various dimensions to determine the effect of the size and shape of the electrode surface on the direct electrical connection between CODH and electrode surface. The results showed the degree of proximity between the CODH cofactor and electrode surface, which varied with AuNP size and caused significant changes to the electrical connection at the interface as well as to the substrate accessibility. Consequently, a high-density nanoscale SRS was fabricated on electrode to further facilitate direct electrical connection as well as to enable distribution of CODH into monolayer or near-monolayer for lowering the barrier of CO diffusion toward enzyme. The findings show the feasibility of controlling the direct electrical connection between CODH and the electrode as well as controlling the substrate accessibility.