Bioelectrochemical fuel cell and sensor based on a quinoprotein, alcohol dehydrogenase

Isolation and Characterization of Homologically Expressed Methanol Dehydrogenase from Methylorubrum extorquens AM1 for the Development of Bioelectrocatalytical Systems

(Ca²⁺)-dependent pyrroloquinolinequinone (PQQ)-dependent methanol dehydrogenase (MDH) (EC: 1.1.2.7) is one of the key enzymes of primary C1-compound metabolism in methylotrophy. PQQ-MDH is a promising catalyst for electrochemical biosensors and biofuel cells. However, the large-scale use of PQQ-MDH in bioelectrocatalysis is not possible due to the low yield of the native enzyme. Homologously overexpressed MDH was obtained from methylotrophic bacterium Methylorubrum extorquens AM1 by cloning the gene of only one subunit, mxaF. The His-tagged enzyme was easily purified by immobilized metal ion affinity chromatography (36% yield). A multimeric form (α6β6) of recombinant PQQ-MDH possessing enzymatic activity (0.54 U/mg) and high stability was demonstrated for the first time. pH-optimum of the purified protein was about 9–10; the enzyme was activated by ammonium ions. It had the highest affinity toward methanol (K_M = 0.36 mM). The recombinant MDH was used for the fabrication of an amperometric biosensor. Its linear range for methanol concentrations was 0.002–0.1 mM, the detection limit was 0.7 µM. The properties of the invented biosensor are competitive to the analogs, meaning that this enzyme is a promising catalyst for industrial methanol biosensors. The developed simplified technology for PQQ-MDH production opens up new opportunities for the development of bioelectrocatalytic systems.

Recent progress of graphene based nanomaterials in bioelectrochemical systems

The application of graphene (Gr) to microbial fuel cells (MFCs) and microbial electrolysis cell (MECs) is considered a very promising approach in terms of enhancing their performance. The superior Gr properties of high electrical and thermal conductivities, along with: superior specific surface area, high electron mobility, and mechanical strength, are the key features that endorse this. Factors impeding the advancement of a microbial fuel cell into commercialization involve primarily the cost of their components, and their production on a small scale. Gr with such outstanding characteristics can help mitigate these challenges, when used as electrode material. The application of Gr as an anode material improves the efficiency of electron transfer and bacterial attachment. When used as a cathode material, it supports the oxygen reduction reaction. This investigation, presents a thorough analysis of the feasibility of Gr as an electrode material in both MFC and MEC applications - based on experimental results from the investigation. Current technological advancements in the implementation of Gr in MFC and MEC are also highlighted in this review. To summarise, the investigation exposes critical issues impeding the advancement of microbial fuel cells, and proposes possible solutions to mitigate these challenges.

Direct Catalytic Fuel Cell Device Coupled to Chemometric Methods to Detect Organic Compounds of Pharmaceutical and Biomedical Interest

Making use of a small direct methanol fuel cell device (DMFC), used as an analytical sensor, chemometric methods, organic compounds very different from one another, can be determined qualitatively and quantitatively. In this research, the following seven different organic compounds of pharmaceutical and biomedical interest, having in common only one –OH group, were considered: chloramphenicol, imipenem, methanol, ethanol, propanol, atropine and cortisone. From a quantitative point of view, the traditional approach, involving the building of individual calibration curves, which allow the quantitative determination of the corresponding organic compounds, even if with different sensitivities, was followed. For the qualitative analysis of each compound, this approach has been much more innovative. In fact, by processing the data from each of the individual response curves, obtained through the fuel cell, using chemometric methods, it is possible to directly identify and recognize each of the seven organic compounds. Since the study is a proof of concept to show the potential of this innovative methodological approach, based on the combination of direct methanol fuel cell with advanced chemometric tools, at this stage, concentration ranges that may not be the ones found in some real situations were investigated. The three methods adopted are all explorative methods with very limited computation costs, which have different characteristics and, therefore, may provide complementary information on the analyzed data. Indeed, while PCA (principal components analysis) provides the most parsimonious summary of the variability observed in the current response matrix, the analysis of the current response behavior was performed by the “slicing” method, in order to transform the current response profiles into numerical matrices, while PARAFAC (Parallel Factor Analysis) allows to obtain a finer deconvolution of the exponential curves. On the other hand, the multiblock nature of “ComDim” (Common Components and Specific Weight Analysis) has been the basis to relate the variability observed in the current response behavior with the parameters of the linear calibrations.

Mediated Fuel Cells: Soluble Redox Mediators and Their Applications to Electrochemical Reduction of O2 and Oxidation of H2, Alcohols, Biomass, and Complex Fuels

Mediated fuel cells are electrochemical devices that produce power in a manner similar to that of conventional proton exchange membrane fuel cells (PEMFCs). They differ from PEMFCs in their use of redox mediators dissolved in liquid electrolyte to conduct oxidation of the fuel or reduction of the oxidant, typically O2, in bulk solution. The mediators transport electrons (and often protons) between the electrode and the catalysts or chemical reagents in solution. This strategy can help overcome many of the challenges associated with conventional fuel cells, including managing complex multiphase reactions (as in O2 reduction) or the use of challenging or heterogeneous fuels, such as hydrocarbons, polyols, and biomass. Mediators are also commonly used in enzymatic fuel cells, where direct electron transfer from the electrode to the enzymatic active site can be slow. This review provides a comprehensive survey of historical and recent mediated fuel cell efforts, including applications using chemical and enzymatic catalysts.

Direct Methanol (or Ethanol) Fuel Cell as Enzymatic or Non-Enzymatic Device, Used to Check Ethanol in Several Pharmaceutical and Forensic Samples

It was already demonstrated by our research group that a direct catalytic methanol (or ethanol) fuel cell (DMFC) device can be used also for analytical purposes, such as the determination of ethanol content in beverages. In the present research we extended the application to the analysis of several ethanol-based pharmaceutical products, i.e., pharmaceutical tinctures (dyes) and disinfectants. In recent work we have also shown that the use of alcohol dehydrogenase enzyme as a component of the anodic section of a direct catalytic methanol (or ethanol) fuel cell significantly improves the performance of a simple DMFC device, making it more suitable to measure ethanol (or methanol) in real samples by this cell. At the same time, we have also shown that DMFC can respond to certain organic compounds that are more complex than methanol and ethanol and having R(R')CH-OH group in the molecule. Firstly, pharmaceutical dyes were analyzed for their ethanol content using the simple catalytic DMFC device, with good accuracy and precision. The results are illustrated in the present paper. Additionally, a detailed investigation carried out on commercial denatured alcoholic samples evidenced several interferences due to the contained additives. Secondly, we hypothesized that by using the enzymatic fuel cell it would be possible to improve the determination, for instance, of certain antibiotics, such as imipenem, or else carry out determinations of ethanol content in saliva and serum (simulating forensic tests, correlated to drivers "breath test"); even if this has already been hypothesized in previous papers, the present study is the first to perform them experimentally, obtaining satisfactory results. In practice, all of the goals which we proposed were reached, confirming the remarkable opportunities of the enzymatic (or non-enzymatic) DMFC device.

Optimization of Glucose Powered Biofuel Cell Anode Developed by Polyaniline-Silver as Electron Transfer Enhancer and Ferritin as Biocompatible Redox Mediator

Polyaniline-silver (PANI-Ag)/ferritin (Frt)/glucose oxidase (GOx) biocompatible anode was utilized for creating power from glucose. The synthesized nanocomposite was investigated by EIS (Electrochemical impedance spectroscopy), XRD (X-ray diffraction), FTIR (Fourier transform infrared spectroscopy), SEM (Scanning electron microscopy), CV (Cyclic voltammetry), and LSV (Linear sweep voltammetry) to know the morphology, crystallinity and electrochemical behaviour of the nanocomposite. The electroactive support (PANI-Ag) was utilized for the immobilization of the enzyme (GOx) and a biocompatible mediator (Frt) to enhance the electrical signals. The electrochemical estimations of the manufactured bioanode were done by utilizing cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The current density obtained by the PANI-Ag/Frt/GOx bioanode was observed to be 25.40 ± 2 mA cm-2 at 40 mM of glucose concentration at a scan rate of 100 mVs-1.

Bringing inorganic chemistry to life with inspiration from R. J. P. Williams

Our appreciation of the scholarly ideas and thinking of Bob Williams is illustrated here by a few of the areas in which he inspired us. His journey to bring inorganic chemistry to life began with an early interest in analytical chemistry, rationalising the relative stabilities of metal coordination complexes (The Irving-Williams Series), and elucidating the organometallic redox chemistry of vitamin B12. He (and Vallee) recognised that metal ions are in energised (entatic) states in proteins and enzymes, which themselves are dynamic structures of rods and springs. He played a key role in helping Rosenberg to pave the road toward the clinic for the anticancer drug cisplatin. He believed that evolution is not just dependent on DNA, but also on the metallome. Organisms and the environment are one system: does DNA code directly for all the essential elements of life?

[Properties of modified amperometric biosensors based on methanol dehydrogenase and Methylobacterium nodulans cells]

The properties of amperometric biosensors based on methanol dehydrogenase (MDH), Methylobacterium nodulans cells, and the ferrocene-modified carbon paste electrode were investigated. It was shown that the addition ofhydroxyapatite (HA) to a carbon paste increased the sensitivity and operating stability of MDH biosensors. The linear range of the electrode was 0.0135-0.5 and 0.032-1.5 mM for methanol and formaldehyde, respectively. The detection limit of methanol and formaldehyde was 4.5 and 11.0 microM, respectively. The loss of activity of the electrode within 10 days of storage in the presence of 2.0 mM KCN did not exceed 12%. Cyanide (10 mM) completely inhibited the sensor responses to formaldehyde (1.0 mM), which allowed for the selective determination of methanol in the presence of formaldehyde. The biosensor based on cells exhibited lower stability and sensitivity toward methanol and formaldehyde; the sensitivity coefficients were 980 and 21 nA/mM, respectively.

Cholesterol self-powered biosensor

Monitoring the cholesterol level is of great importance, especially for people with high risk of developing heart disease. Here we report on reagentless cholesterol detection in human plasma with a novel single-enzyme, membrane-free, self-powered biosensor, in which both cathodic and anodic bioelectrocatalytic reactions are powered by the same substrate. Cholesterol oxidase was immobilized in a sol-gel matrix on both the cathode and the anode. Hydrogen peroxide, a product of the enzymatic conversion of cholesterol, was electrocatalytically reduced, by the use of Prussian blue, at the cathode. In parallel, cholesterol oxidation catalyzed by mediated cholesterol oxidase occurred at the anode. The analytical performance was assessed for both electrode systems separately. The combination of the two electrodes, formed on high surface-area carbon cloth electrodes, resulted in a self-powered biosensor with enhanced sensitivity (26.0 mA M(-1) cm(-2)), compared to either of the two individual electrodes, and a dynamic range up to 4.1 mM cholesterol. Reagentless cholesterol detection with both electrochemical systems and with the self-powered biosensor was performed and the results were compared with the standard method of colorimetric cholesterol quantification.

Bioelectrocatalysis-based application of quinoproteins and quinoprotein-containing bacterial cells in biosensors and biofuel cells

Electrochemical studies on the applied aspects of quinoproteins are briefly reviewed. Catalytic reactions of quinoprotein enzymes can be connected to electrochemical reactions directly or by the mediation of molecules functioning as electron acceptors of the enzymes. Such an enzyme-electrochemical reaction is called bioelectrocatalysis. It provides a novel method of kinetic analysis of enzyme catalysis and even whole bacterial cell catalysis. The principle of bioelectrocatalysis is first described, then, the bioelectrocatalysis-based application of quinoproteins in biosensors is mentioned. Characteristics and performance of this type of biosensor is explained by citing our own work. Possible application in bioreactors and biofuel cells is also mentioned.

A miniature biofuel cell operating in a physiological buffer

A glucose-O2 biofuel cell, consisting only of two electrocatalyst coated 7-mum diameter, 2-cm long carbon fibers is reported. The cell operated continuously at 0.52 V at 37 degrees C in a physiological buffer solution for a week, producing 1.9 muW during the first and 1.0 muW during the last day, generating in the period 0.9 J of electrical energy while passing a charge of 1.7 C. If a similar dimension zinc fiber were utilized in a battery at 100% current efficiency, only 0.016 C would have been generated.

Investigation of a simple amperometric electrode system to rapidly quantify and detect bacteria in foods

A two electrode system mounted as a single probe was developed to measure electrochemically the rate of reduction of a redox mediator (thionine) by bacteria. The system gave a rapid (2 min) bacterial-dependent current above 2.5 x 10(5) cfu/ml with pure cultures of bacteria, but when applied to the measurement of the bacterial contamination in samples of meat and milk it was unable to detect or quantify the contamination reliably. Incubation of samples for a few hours before examination enabled the system to detect bacteria in excess of 10(6) cfu/ml.

Direct and indirect electron transfer between electrodes and redox proteins

The direct electrochemistry of redox proteins has been achieved at a variety of electrodes, including modified gold, pyrolytic graphite and metal oxides. Careful design of electrode surfaces and electrolyte conditions are required for the attainment of rapid and reversible protein-electrode interaction. The electron transfer reactions of more complex systems, such as redox enzymes, are now being examined. The 'well-behaved' electrochemistry of redox proteins can be usefully exploited by coupling the electrode reaction to enzymes for which the redox proteins act as cofactors. In systems where direct electron transfer is very slow, small electron carriers, or mediators, may be employed to enhance the rate of electron exchange with the electrode. The organometallic compound ferrocene and its derivatives have proved particularly effective in this role. A new generation of electrochemical biosensors employs ferrocene derivatives as mediators.