Nanocatalysts Containing Direct Electron Transfer-Capable Oxidoreductases: Recent Advances and Applications

Direct electron transfer (DET)-capable oxidoreductases are enzymes that have the ability to transfer/receive electrons directly to/from solid surfaces or nanomaterials, bypassing the need for an additional electron mediator. More than 100 enzymes are known to be capable of working in DET conditions; however, to this day, DET-capable enzymes have been mainly used in designing biofuel cells and biosensors. The rapid advance in (semi) conductive nanomaterial development provided new possibilities to create enzyme-nanoparticle catalysts utilizing properties of DET-capable enzymes and demonstrating catalytic processes never observed before. Briefly, such nanocatalysts combine several cathodic and anodic catalysis performing oxidoreductases into a single nanoparticle surface. Hereby, to the best of our knowledge, we present the first review concerning such nanocatalytic systems involving DET-capable oxidoreductases. We outlook the contemporary applications of DET-capable enzymes, present a principle of operation of nanocatalysts based on DET-capable oxidoreductases, provide a review of state-of-the-art (nano) catalytic systems that have been demonstrated using DET-capable oxidoreductases, and highlight common strategies and challenges that are usually associated with those type catalytic systems. Finally, we end this paper with the concluding discussion, where we present future perspectives and possible research directions.This article belongs to the Special Issue State of the Art and Future Trends in Nanostructured Biocatalysi

Nanocatalysts containing direct electron transfer-capable oxidoreductases: recent advances and applications

Direct electron transfer (DET)-capable oxidoreductases are enzymes that have the ability to transfer/receive electrons directly to/from solid surfaces or nanomaterials, bypassing the need for an additional electron mediator. More than 100 enzymes are known to be capable of working in DET conditions; however, to this day, DET-capable enzymes have been mainly used in designing biofuel cells and biosensors. The rapid advance in (semi) conductive nanomaterial development provided new possibilities to create enzyme-nanoparticle catalysts utilizing properties of DET-capable enzymes and demonstrating catalytic processes never observed before. Briefly, such nanocatalysts combine several cathodic and anodic catalysis performing oxidoreductases into a single nanoparticle surface. Hereby, to the best of our knowledge, we present the first review concerning such nanocatalytic systems involving DET-capable oxidoreductases. We outlook the contemporary applications of DET-capable enzymes, present a principle of operation of nanocatalysts based on DET-capable oxidoreductases, provide a review of state-of-the-art (nano) catalytic systems that have been demonstrated using DET-capable oxidoreductases, and highlight common strategies and challenges that are usually associated with those type catalytic systems. Finally, we end this paper with the concluding discussion, where we present future perspectives and possible research directions

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

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

Vienasienių nanovamzdelių ir Coprinus Cinereus peroksidazės kompleksų sintezė ir tyrimas

Carbon nanotube-peroxidase conjugates can catalyze oxidation of “Amplex Red“ into fluorescent resorufin so they may be useful as a marker. Synthesis of carbon nanotube-enzyme conjugates was carried out with different starting concentrations of Coprinus Cinereus peroxidase and polyethylenimine, also in the medium with different pH. Specific activity of conjugates was determined spectrophotometrically with 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) and hydrogen peroxide as substrates. The scanning electron and confocal fluorescence microscope analysis were performed on the conjugates. It was concluded that these structures have perspective to be used as fluorescent markers.Anglies nanovamzdelių-peroksidazės kompleksai gali katalizuoti „Amplex Red“ oksidaciją. Proceso metu susidaro fluoresuojantis rezorufinas. Todėl šie kompleksai gali būti naudoajami kaip nanožymenys. Nanovamzdelių fermentinių kompleksų sintezė buvo atlikta su skirtingomis pradinėmis Coprinus Cinereus peroksidazės ir polietilenimino koncentracijomis, taip pat terpėje su skirtingu pH. Gautų kompleksų specifinis aktyvumas buvo nustatytas spektrofotometriškai naudojant 2,2‘-azino-bis-3-etilbenztiazolino-6-sulfoninę rūgštį (ABTS) ir vandenilio peroksidą kaip substratus. Atliktos analizės naudojantis skanuojančiu elektroniniu ir fluoresentiniu konfokaliniu mikroskopu, parodyta, kad kompleksai turi didelį katalitinį pajekumą ir gali būti naudojami kaip fluorescentiniai markeriai. Reikšminiai žodžiai: anglies nanovamzdeliai, peroksidazė, polietileniminas, nanožymenys, specifinis aktyvumas

A 2D-to-3D morphology transitions of gold in organic acid electrolytes: Characterization and application in bioanode design /

The inexpensive, relatively fast and scalable production of nanostructured electrodes may benefit future disposable biosensor technology. In this research, nanoporous gold (NPG) surfaces were successfully fabricated by anodizing the gold in different organic acid, and further used for glucose dehydrogenase (GDH)-based bioanode design. The porosity of NPG layers was manipulated by changing the anodization time, and the dependency of relative electrochemical surface area (rESA) on the bioanode performances was systematically examined. The X-ray photoelectron spectroscopy (XPS) studies of NPG formed in oxalic acid (NPGox) and their depth profiles of Au 4f and O 1s evidenced the chemical state of pure metallic gold (Au0), whereas NPG formed in glycolic acid (NPGgly) has appreciable content of gold oxide and hydroxides. The NPGgly/4-ATP/GDH bioanodes exhibited direct electron transfer (DET-type) bioelectrocatalytic activity, while the highest current densities of 0.35 mA cm- 2 and low onset potential of - 0.189 V (vs. Ag/AgCl) were observed. The electrodes showed longterm stability and, up to three weeks, retained 76 % of their initial value. Furthermore, the biofuel cell possessed the maximum power densities of 31.8 μW cm−2 and open-circuit potential (OCP) differences of 0.441 V, thus evidencing that NPGgly layers could be encouraging for developing biosensors and biofuel cells

Capacitance-based biosensor for the measurement of total loss of L-amino acids in human serum during hemodialysis

In this paper, we present a biosensor based on a gold nanoparticle (AuNP)-modified Pt electrode with an adjusted membrane containing cross-linked L-amino acid oxidase for the detection and quantification of total L-amino acids. The designed biosensor was tested and characterized using the capacitance-based principle, capacitance measurements after electrode polarization, disconnection from the circuit, and addition of the respective amount of the analyte. The method was implemented using the capacitive and catalytic properties of the Pt/AuNP electrode; nanostructures were able to store electric charge while at the same time catalyzing the oxidation of the redox reaction intermediate H2O2. In this way, the Pt/AuNP layer was charged after the addition of analytes, allowing for much more accurate measurements for samples with low amino acid concentrations. The combined biosensor electrode with the capacitance-based measurement method resulted in high sensitivity and a low limit of detection (LOD) for hydrogen peroxide (4.15 μC/μM and 0.86 μM, respectively) and high sensitivity, a low LOD, and a wide linear range for L-amino acids (0.73 μC/μM, 5.5 μM and 25–1500 μM, respectively). The designed biosensor was applied to measure the relative loss of amino acids in patients undergoing renal replacement therapy by analyzing amino acid levels in diluted serum samples before and after entering/leaving the hemodialysis apparatus. In general, the designed biosensor in conjunction with the proposed capacitance-based method was clinically tested and could also be applied for the detection of other analytes using analyte-specific oxidases

Laccase-gold nanoparticle assisted bioelectrocatalytic reduction of oxygen

It was found that homogeneous activity of Trametes hirsuta laccase is considerably diminished in the presence of gold nanoparticles (Au-NPs). Heterogeneous electron transfer studies revealed that Au-NPs facilitate direct electron transfer (DET) between the T1 copper site of the laccase and the surface of Au-NP modified electrodes. DET was characterized by the standard heterogeneous ET constant of 0.5 +/- 0.6 s(-1) at Au-NPs with an average diameter of 50 nm. As a consequence of this a well pronounced DET based bioelectrocatalytic oxygen reduction with current densities of 5-30 mu A cm(-2) has been achieved at the laccase-Au-NP modified electrodes

Direct electron transfer reactions between human ceruloplasmin and electrodes.

In an effort to find conditions favouring bioelectrocatalytic reduction of oxygen by surface-immobilised human ceruloplasmin (Cp), direct electron transfer (DET) reactions between Cp and an extended range of surfaces were considered. Exploiting advances in surface nanotechnology, bare and carbon-nanotube-modified spectrographic graphite electrodes as well as bare, thiol- and gold-nanoparticle-modified gold electrodes were considered, and ellipsometry provided clues as to the amount and form of adsorbed Cp. DET was studied under different conditions by cyclic voltammetry and chronoamperometry. Two Faradaic processes with midpoint potentials of about 400 mV and 700 mV vs. NHE, corresponding to the redox transformation of copper sites of Cp, were clearly observed. In spite of the significant amount of Cp adsorbed on the electrode surfaces, as well as the quite fast DET reactions between the redox enzyme and electrodes, bioelectrocatalytic reduction of oxygen by immobilised Cp was never registered. The bioelectrocatalytic inertness of this complex multi-functional redox enzyme interacting with a variety of surfaces might be associated with a very complex mechanism of intramolecular electron transfer involving a kinetic trapping behaviour