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Carbenes with conjugatively connected redox system act as “auto‐umpolung” ligands. Due to their electronic flexibility, they should also be particularly suitable to stabilize open‐shell species. Herein, the first neutral radical of such sort is described in form of a dialkylamino‐substituted bis(dicyanomethylene)cyclopropanide. Despite the absence of steric shielding, the radical is stable for an extended amount of time and was consequently characterized in solution via EPR measurements. These data and accompanying X‐ray structural analyses indicate that the radical species is in equilibrium with aggregates (formed via π‐stacking) and dimers (obtained via σ‐bond formation between methylene carbons).

We report on a photobioelectrochemical fuel cell consisting of a glucose‐oxidase‐modified BiFeO3 photobiocathode and a quantum‐dot‐sensitized inverse opal TiO2 photobioanode linked to FAD glucose dehydrogenase via a redox polymer. Both photobioelectrodes are driven by enzymatic glucose conversion. Whereas the photobioanode can collect electrons from sugar oxidation at rather low potential, the photobiocathode shows reduction currents at rather high potential. The electrodes can be arranged in a sandwich‐like manner due to the semi‐transparent nature of BiFeO3, which also guarantees a simultaneous excitation of the photobioanode when illuminated via the cathode side. This tandem cell can generate electricity under illumination and in the presence of glucose and provides an exceptionally high OCV of about 1 V. The developed semi‐artificial system has significant implications for the integration of biocatalysts in photoactive entities for bioenergetic purposes, and it opens up a new path toward generation of electricity from sunlight and (bio)fuels., A photobioelectrochemical tandem cell is presented in which two photoelectrodes have been functionally coupled with two biocatalysts for supplying the light‐driven reaction with charge carriers from glucose conversion. The cell allows the generation of electricity from biofuels and light with a high open‐circuit voltage of 1 V.

Biohybrid photoelectrochemical systems in photovoltaic or biosensor applications have gained considerable attention in recent years. While the photoactive proteins engaged in such systems usually maintain an internal charge separation quantum yield of nearly 100%, the subsequent steps of electron and hole transfer beyond the protein often limit the overall system efficiency and their kinetics remain largely uncharacterized. To reveal the dynamics of one of such charge-transfer reactions, we report on the reduction of Rhodobacter sphaeroides reaction centers (RCs) by Os-complex-modified redox polymers (P-Os) characterized using transient absorption spectroscopy. RCs and P-Os were mixed in buffered solution in different molar ratios in the presence of a water-soluble quinone as an electron acceptor. Electron transfer from P-Os to the photoexcited RCs could be described by a three-exponential function, the fastest lifetime of which was on the order of a few microseconds, which is a few orders of magnitude faster than the internal charge recombination of RCs with fully separated charge. This was similar to the lifetime for the reduction of RCs by their natural electron donor, cytochrome c2. The rate of electron donation increased with increasing ratio of polymer to protein concentrations. It is proposed that P-Os and RCs engage in electrostatic interactions to form complexes, the sizes of which depend on the polymer-to-protein ratio. Our findings throw light on the processes within hydrogel-based biophotovoltaic devices and will inform the future design of materials optimally suited for this application.

Well‐defined assemblies of photosynthetic protein complexes are required for an optimal performance of semi‐artificial energy conversion devices, capable of providing unidirectional electron flow when light‐harvesting proteins are interfaced with electrode surfaces. We present mixed photosystem I (PSI) monolayers constituted of native cyanobacterial PSI trimers in combination with isolated PSI monomers from the same organism. The resulting compact arrangement ensures a high density of photoactive protein complexes per unit area, providing the basis to effectively minimize short‐circuiting processes that typically limit the performance of PSI‐based bioelectrodes. The PSI film is further interfaced with redox polymers for optimal electron transfer, enabling highly efficient light‐induced photocurrent generation. Coupling of the photocathode with a [NiFeSe]‐hydrogenase confirms the possibility to realize light‐induced H2 evolution., Towards the development of improved biophotovoltaic devices for solar energy conversion, a mixed monolayer constituted by photosystem I trimers and monomers enables the fabrication of highly efficient biophotoelectrodes by minimizing electronic short‐circuiting processes while at the same time ensuring a high density of photoactive molecules per unit area.

Wir berichten über ein auf einem Polymer basierendes,elektroenzymatisches Stickstofffixierungssystem unter Verwendung eines metallfreien Redoxpolymers – mit Neutralrot modifiziertes Poly(glycidylmethacrylat-co-methylmethacrylat- co-poly(ethylenglycol)methacrylat), das ein niedriges Redoxpotential von 0.58 V vs. SCE besitzt. Die stabile und effiziente elektrische Kontaktierung der Nitrogenase innerhalb der Redoxpolymermatrix ermöglicht eine mediierte Bioelektrokatalyse von N3-, NO2- und N2 zu NH3, die durch das MoFe-Protein über die polymergebundenen Redoxeinheiten, die in der Polymermatrix verteilt sind, katalysiert wird. Elektrolyse produzierte 209±30 nmol NH3nmol MoFe-1h-1 durch N2-Reduktion. Die biosynthetische N2-Reduktion zu NH3 wurde durch 15N2-Markierungsexperimente und NMR-Analysen bestätigt.

The incorporation of highly active but also highly sensitive catalysts (e.g. the [FeFe] hydrogenase from Desulfovibrio desulfuricans) in biofuel cells is still one of the major challenges in sustainable energy conversion. We report the fabrication of a dual-gas diffusion electrode H2 /O2 biofuel cell equipped with a [FeFe] hydrogenase/redox polymer-based high-current-density H2 -oxidation bioanode. The bioanodes show benchmark current densities of around 14 mA cm-2 and the corresponding fuel cell tests exhibit a benchmark for a hydrogenase/redox polymer-based biofuel cell with outstanding power densities of 5.4 mW cm-2 at 0.7 V cell voltage. Furthermore, the highly sensitive [FeFe] hydrogenase is protected against oxygen damage by the redox polymer and can function under 5 % O2 .

The fabrication and electrochemical evaluation of transparent photoelectrodes consisting of Photosystem I (PSI) or Photosystem II (PSII) is described, which are embedded and electrically wired by a redox polymer. The fabrication process is performed by an automated airbrush-type spray coating system, which ensures controlled and scalable electrode preparation. As proof of concept, electrodes with a surface area of up to 25 cm2 were prepared. The macro-porous structure of the indium tin oxide electrodes allows a high loading of the photoactive protein complexes leading to enhanced photocurrents, which are essential for potentially technologically relevant solar-powered devices. In addition, we show that unpurified crude PSII extracts, which can be provided in comparatively high yields for electrode modification, are suitable for photoelectrode fabrication with comparable photocurrent densities.

Variants of the highly active [NiFeSe] hydrogenase from D. vulgaris Hildenborough that exhibit enhanced O2 tolerance were used as H2‐oxidation catalysts in H2/O2 biofuel cells. Two [NiFeSe] variants were electrically wired by means of low‐potential viologen‐modified redox polymers and evaluated with respect to H2‐oxidation and stability against O2 in the immobilized state. The two variants showed maximum current densities of (450±84) μA cm−2 for G491A and (476±172) μA cm−2 for variant G941S on glassy carbon electrodes and a higher O2 tolerance than the wild type. In addition, the polymer protected the enzyme from O2 damage and high‐potential inactivation, establishing a triple protection for the bioanode. The use of gas‐diffusion bioanodes provided current densities for H2‐oxidation of up to 6.3 mA cm−2. Combination of the gas‐diffusion bioanode with a bilirubin oxidase‐based gas‐diffusion O2‐reducing biocathode in a membrane‐free biofuel cell under anode‐limiting conditions showed unprecedented benchmark power densities of 4.4 mW cm−2 at 0.7 V and an open‐circuit voltage of 1.14 V even at moderate catalyst loadings, outperforming the previously reported system obtained with the [NiFeSe] wild type and the [NiFe] hydrogenase from D. vulgaris Miyazaki F., Triple protection: A stable, high‐current‐density‐based H2‐oxidation bioanode is presented. It is equipped with [NiFeSe] variants that show enhanced O2 tolerance, which are immobilized and wired to electrode surfaces with a low‐potential viologen‐modified polymer. The polymer acts simultaneously as a high‐potential and O2 shield. The triply protected bioanodes are incorporated in membrane‐free biofuel cells, which reveal benchmark performances at moderate catalyst loading.

Photosystem II (PSII) is the only enzyme that catalyzes light-induced water oxidation, the basis for its application as a biophotoanode in various bio-photovoltaics and photo-bioelectrochemical cells. However, the absorption spectrum of PSII limits the quantum efficiency in the range of visible light, due to a gap in the green absorption region of chlorophylls (500–600 nm). To overcome this limitation, we have stabilized the interaction between PSII and Phycobilisomes (PBSs) – the cyanobacterial light harvesting complex, in vitro. The PBS of three different cyanobacteria (Acaryochloris marina, Am, Mastigocladus laminosus, ML, and Synechocystis sp. PCC 6803, Syn) are analyzed for their ability to transfer energy to Thermosynechococcus elongatus (Te) PSII by fluorescence spill-over and photo-current action spectra. Integration of the PBS–PSII super-complexes within an Os-complex-modified hydrogel on macro-porous indium tin oxide electrodes (MP-ITO) resulted in notably improved, wavelength dependent, incident photon-to-electron conversion efficiencies (IPCE). IPCE values in the green gap were doubled from 3% to 6% compared to PSII electrodes without PBS and a maximum IPCE up to 10.9% at 670 nm was achieved.

We describe the fabrication of gas diffusion electrodes modified with polymer/enzyme layers for electroenzymatic CO2 fixation. For this, a metal-free organic low-potential viologen-modified polymer...

Bioelectrocatalysis provides access to sustainable and highly efficient technological applications. However, several limitations related either to the intrinsic properties of the biocatalyst or to technical difficulties still hamper or even prevent the integration of such devices into technologically relevant large-scale processes. In this Review, we challenge the common viewpoint suggesting biology-based catalytic systems as a promising approach for the provision of sustainable stored energy and discuss the status of bioelectrocatalytic devices developed for energy conversion. In particular, we focus on two major research areas in the field, that is, H2-powered hydrogenase-based biofuel cells and biophotoelectrodes for solar energy harvesting. We identify the main limitations that have to be addressed to gain access to applied large-scale bio-based and bio-inspired advanced energy conversion systems. Moreover, we show recent examples and milestones that are paving the way towards potential realization of these technologies by overcoming existing limiting factors. Bioelectrocatalysis provides access to sustainable and highly efficient technological applications, but several limitations still prevent the large-scale integration of such devices. This Review discusses the current status of hydrogenase-based biofuel cells and biophotoelectrodes for solar energy harvesting.

Following inspiration by natural photosynthesis, the design and fabrication of semi-artificial biophotoelectrochemical devices able to harvest solar energy and aiming on the implementation of green and sustainable energy conversion systems is presently an important field of research. Here we present the development of a fully light-driven biosupercapacitor fabricated by incorporation of isolated photosystem 2 and photosystem 1 protein complexes embedded within the same Os-complex modified redox polymer. By this, light energy is stored at both electrodes within the polymer-based pseudocapacitive matrix in the form of Os3+ centers at the photosystem1-based biocathode and in the form of Os2+ centers at the photosystem 2-based bioanode. The stored energy can be released on demand into bursts of electricity. Due to the purely light-driven self-charging process, the biosupercapacitor provided a power output of 1.0 μW cm−2 after 200 s charging time. Moreover, the use of different electrode materials and their implication on the performance of the implemented biodevice is evaluated.

We report an amperometric biosensor for the urinary disease biomarker para-hydroxyphenylacetate ( p-HPA) in which the allosteric reductase component of a bacterial hydroxylase, C1-hpah, is electrically wired to glassy carbon electrodes through incorporation into a low-potential Os-complex modified redox polymer. The proposed biosensing strategy depends on allosteric modulation of C1-hpah by the binding of the enzyme activator and analyte p-HPA, stimulating oxidation of the cofactor NADH. The pronounced concentration-dependence of allosteric C1-hpah modulation in the presence of a constant concentration of NADH allowed sensitive quantification of the target, p-HPA. The specific design of the immobilizing redox polymer with suitably low working potential allowed biosensor operation without the risk of co-oxidation of potentially interfering substances, such as uric acid or ascorbic acid. Optimized sensors were successfully applied for p-HPA determination in artificial urine, with good recovery rates and reproducibility and sub-micromolar detection limits. The proposed application of the allosteric enzyme C1-hpah for p-HPA trace electroanalysis is the first successful example of simple amperometric redox enzyme/redox polymer biosensing in which the analyte acts as an effector, modulating the activity of an immobilized biocatalyst. A general advantage of the concept of allosterically modulated biosensing is its ability to broaden the range of approachable analytes, through the move from substrate to effector detection.

The immobilization, protection, and electrical wiring of sensitive catalysts by specifically designed supporting matrixes are of particular importance for technological relevant applications. Here,...

The development of bioelectrochemical assemblies for sustainable energy transformation constitutes an increasingly important field of research. Significant progress has been made in the development of semiartificial devices for conversion of light into electrical energy by integration of photosynthetic biomolecules on electrodes. However, sufficient long-term stability of such biophotoelectrodes has been compromised by reactive species generated under aerobic operation. Therefore, meeting the requirements of practical applications still remains unsolved. We present the operation of a photosystem I-based photocathode using an electron acceptor that enables photocurrent generation under anaerobic conditions as the basis for a biodevice with substantially improved stability. A continuous operation lifetime considerably superior to previous reports and at higher light intensities is paving the way toward the potential application of semiartificial energy conversion devices.

A biohybrid photobioanode mimicking the Z-scheme has been developed by functional integration of photosystem II (PSII) and PbS quantum dots (QDs) within an inverse opal TiO2 architecture giving rise to a rather negative water oxidation potential of about -0.55 V vs. Ag/AgCl, 1 m KCl at neutral pH. The electrical linkage between both light-sensitive entities has been established through an Os-complex-modified redox polymer (POs ), which allows the formation of a multi-step electron-transfer chain under illumination starting with the photo-activated water oxidation at PSII followed by an electron transfer from PSII through POs to the photo-excited QDs and finally to the TiO2 electrode. The photobioanode was coupled to a novel, transparent, inverse-opal ATO cathode modified with an O2 -reducing bilirubin oxidase for the construction of a H2 O/O2 photobioelectrochemical cell reaching a high open-circuit voltage of about 1 V under illumination.

Photosynthetic protein complexes are attractive building blocks for the fabrication of semi-artificial energy conversion devices. However, limitations in the efficiency of the implemented biophotovoltaic systems prevent their use in practical applications. In particular, the effective minimization of recombination processes in photosystem I (PSI) modified bioelectrodes is crucial for enabling a unidirectional electron flow allowing the true potential of the large charge separation at PSI being exploited. Here, we present controlled immobilization of PSI monolayers with a predefined preferential orientation that translates into anisotropic electron flow upon irradiation. Further interface of the oriented PSI monolayer with redox polymers allows an efficient electron transfer and minimization of possible short-circuiting pathways. To complete the functional biophotocathode, the PSI monolayer is coupled to a hydrogenase (H2ase) to realize light-induced H2 evolution. The PSI/H2ase biocathode is then combined with a redox polymer/photosystem II-based bioanode demonstrating a fully light-driven Z-scheme mimic biophotovoltaic cell for bias-free water splitting.

Photosystem I (PSI), a robust and abundant biomolecule capable of delivering high-energy photoelectrons, has a great potential for the fabrication of light-driven semi-artificial bioelectrodes. Although possibilities have been explored in this regard, the true capabilities of this technology have not been achieved yet, particularly for their use as bioanodes. Here, the use of PSI Langmuir monolayers and their electrical wiring with specifically designed redox polymers is shown, ensuring an efficient mediated electron transfer as the basis for the fabrication of an advanced biophotoanode. The bioelectrode is rationally implemented and optimized for enabling the generation of substantial photocurrents of up to 17.6 μA cm−2 and is even capable of delivering photocurrents at potentials as low as −300 mV vs standard hydrogen electrode, surpassing the performance of comparable devices. To highlight the applicability of the developed light-driven bioanode, a biophotovoltaic cell is assembled in combination with a gas-breathing biocathode. The assembly operates in a single compartment cell and delivers considerable power outputs at large cell voltages. The implemented biophotoanode constitutes an important step toward the development of advanced biophotovoltaic devices.

We report an organic redox‐polymer‐based electroenzymatic nitrogen fixation system using a metal‐free redox polymer, namely neutral‐red‐modified poly(glycidyl methacrylate‐co‐methylmethacrylate‐co‐poly(ethyleneglycol)methacrylate) with a low redox potential of −0.58 V vs. SCE. The stable and efficient electric wiring of nitrogenase within the redox polymer matrix enables mediated bioelectrocatalysis of N3 −, NO2 − and N2 to NH3 catalyzed by the MoFe protein via the polymer‐bound redox moieties distributed in the polymer matrix in the absence of the Fe protein. Bulk bioelectrosynthetic experiments produced 209±30 nmol NH3 nmol MoFe−1 h−1 from N2 reduction. 15N2 labeling experiments and NMR analysis were performed to confirm biosynthetic N2 reduction to NH3., Fixed in the matrix: An electroenzymatic ammonia‐producing system is demonstrated using nitrogenase immobilized within a specifically designed neutral‐red‐modified redox polymer. Efficient electric wiring of nitrogenase in the redox polymer matrix enabled mediated bioelectrocatalysis and thereby facilitated biosynthetic N2 fixation in the absence of ATP and Fe protein.

The incorporation of highly active but also highly sensitive catalysts (e.g. the [FeFe] hydrogenase from Desulfovibrio desulfuricans) in biofuel cells is still one of the major challenges in sustainable energy conversion. We report the fabrication of a dual‐gas diffusion electrode H2/O2 biofuel cell equipped with a [FeFe] hydrogenase/redox polymer‐based high‐current‐density H2‐oxidation bioanode. The bioanodes show benchmark current densities of around 14 mA cm−2 and the corresponding fuel cell tests exhibit a benchmark for a hydrogenase/redox polymer‐based biofuel cell with outstanding power densities of 5.4 mW cm−2 at 0.7 V cell voltage. Furthermore, the highly sensitive [FeFe] hydrogenase is protected against oxygen damage by the redox polymer and can function under 5 % O2., A highly active but extremely O2‐sensitive [FeFe] hydrogenase that acts as a H2‐oxidation catalyst in a H2/O2 biofuel cell is integrated in a shielded bioanode and a membrane‐free H2/O2 biofuel cell. The enzyme was wired to gas diffusion electrodes by means of a viologen‐modified redox polymer matrix. Outstanding current densities of up to 14 mA cm−2 and power outputs of 5.5 mW cm−2 in a membrane‐free device were achieved.

A light-controlled multiplexing platform has been developed on the basis of a quantum dot-sensitized inverse opal TiO2 electrode with integrated biocatalytic reactions. Spatially resolved illumination enables multiplexed sensing and imaging of enzymatic oxidation reactions at relatively negative applied potentials.

Robotic electroanalysis in 24-well microplates was used to determine Paracetamol (PCT) release from thin films of chitosan and two pH-sensitive synthetic polymers as well as blends of the polymers with each other and with agarose. Square-wave voltammograms were recorded automatically in a potential window of 0.35 V-0.85 V vs. Ag/AgCl/0.1 M KCl and their evaluation revealed time-dependent PCT release into acidic and basic media. Comparison of the release profiles showed that pure chitosan layers released PCT quickly in a single-phase process while liberation from synthetic polymer thin films was slower with a sigmoidal shape at pH 1.2 and pH 8.0 with a maximum release of PCT after approximately 150 and 140 min, respectively. The release profile from thicker agarose films was between those of the thin films. Agarose blended with chitosan or synthetic polymers formed films with biphasic release behavior. Chitosan linearized the initial section of the release profile in chitosan/polymer blends. The automated procedure for release testing offers the advantage of low-cost, labor-effective and error-free data acquisition. The procedure has been validated as a useful microplate assay option for release profile testing.

In the present "genomic era" and developing world of DNA chips DNA detection based on intercalation of specific molecules is of particular interest because the detection process is largely indepen-dent of the sequence of the target DNA. In this work, an acridine orange based intercalator, which was tethered to deglycosylated glucose oxidase was ad-hoc synthesized and investigated towards its ability for the interaction with dsDNA. Amperometric detection of the DNA hybridization was done by signal amplification based on the catalytic oxidation of glucose by DNA-bound glucose oxidase. A clear distinction between dsDNA and ssDNA was achieved owing to a carefully designed DNA-modified electrode surface and prevention of unspecific adsorption of the acridinium orange modified enzyme by implementing a potential-assisted immobilization method for the fabri¬cation of DNA sensing platforms.

Carbon nanoelectrodes in the sub-micron range were modified with an enzyme cascade immobilized in a spatially separated polymer double layer system for the detection of glutamate at the cellular level. The enzyme cascade consists of glutamate oxidase (GlutOx) that was immobilized in a hydrophilic redox silent polymer on top of a horseradish peroxidase (HRP)/redox polymer layer. In the presence of O2, glutamate was oxidized under concomitant reduction of O2 to H2O2 at GlutOx. H2O2 is further reduced to water by means of HRP and electrons are shuttled via the redox polymer matrix that wires the HRP to the electrode surface, hence delivering a current response proportional to the glutamate concentration. The nanometer-sized sensors could be successfully used to measure glutamate release from primary mouse astrocytes in 10 mM HEPES buffer.

Summary Autonomous bioelectrochemical devices have been described since the beginning of the 21st century. The properties and broad potential applications of such devices encouraged the development of a plethora of examples. Self-powered biodevices have been mainly used for sensing applications with different strategies reported for the detection of various important analytes. Moreover, these devices had also inspired the design and fabrication of logic- and biocomputing-based systems with further applications in logic-activated drug release for the development of sense-act-treat systems. In addition, their use as self-sustained systems for energy supply has been recently reported. This review summarizes the development and progress of self-powered biodevices with particular attention to latest advances and novel applications.

In the development of semi-artificial biophotovoltaic assemblies, deeper understanding of electrochemical processes is required to achieve functional and efficient devices. Evaluation of photosystem 2 embedded in an Os-complex modified redox polymer using scanning photoelectrochemical microscopy (SPECM) provides insight into the intricate electrochemical processes of the immobilized protein complex and its electrical communication pathways with the redox tethers of the polymer matrix. The use of local irradiation during an SPECM array scan prevents sample inactivation prior to analysis. Moreover, the simultaneously possible collection of partially reduced oxygen species in the form of hydrogen peroxide confirms the presence of competing charge transfer pathways involved in the reduction of oxygen at the chlorophyll pigments upon irradiation of the sample. In addition, evaluation of photocurrent in the presence of an inhibitor that blocks the terminal plastoquinone QB binding site of the photosystem reveals electrochemical communication between the intermediate plastoquinone QA and the redox polymer. The obtained information proves to be relevant for further design and optimization of devices for technological applications.

In the development of biofuel cells great effort is dedicated to achieving outstanding figures of merit, such as high stability, maximum power output, and a large open circuit voltage. Biofuel cells with immobilized redox mediators, such as redox polymers with integrated enzymes, show experimentally a substantially higher open circuit voltage than the thermodynamically expected value. Although this phenomenon is widely reported in the literature, there is no comprehensive understanding of the potential shift, the high open circuit voltages have not been discussed in detail, and hence they are only accepted as an inherent property of the investigated systems. We demonstrate that this effect is the result of a Nernstian shift of the electrode potential when catalytic conversion takes place in the absence or at very low current flow. Experimental evidence confirms that the immobilization of redox centers on the electrode surface results in the assembled biofuel cell delivering a higher power output because of charge storage upon catalytic conversion. Our findings have direct implications for the design and evaluation of (bio)fuel cells with pseudocapacitive elements.

Natural photosynthesis stores sunlight in chemical energy carriers, but it has not evolved for the efficient synthesis of fuels, such as H2. Semi-artificial photosynthesis combines the strengths of natural photosynthesis with synthetic chemistry and materials science to develop model systems that overcome nature’s limitations, such as low-yielding metabolic pathways and non-complementary light absorption by photosystems I and II. Here, we report a bias-free semi-artificial tandem platform that wires photosystem II to hydrogenase for overall water splitting. This photoelectrochemical cell integrated the red and blue light-absorber photosystem II with a green light-absorbing diketopyrrolopyrrole dye-sensitized TiO2 photoanode, and so enabled complementary panchromatic solar light absorption. Effective electronic communication at the enzyme–material interface was engineered using an osmium-complex-modified redox polymer on a hierarchically structured TiO2. This system provides a design protocol for bias-free semi-artificial Z schemes in vitro and provides an extended toolbox of biotic and abiotic components to re-engineer photosynthetic pathways.

The functional coupling of photoactive nanostructures with enzymes creates a strategy for the design of light-triggered biocatalysts. This study highlights the efficient wiring of flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase (FAD-GDH) to PbS quantum dot (QD)-sensitized inverse opal TiO2 electrodes (IO-TiO2) by means of an Os-complex-containing redox polymer for the light-driven glucose oxidation. For the construction of IO-TiO2 scaffolds, a template approach has been developed, enabling the tunability of the surface area and a high loading capacity for the integration of QDs, redox polymer, and enzyme. The biohybrid signal chain can be switched on with light, generating charge carriers within the QDs, triggering a multistep electron-transfer cascade from the enzyme toward the redox polymer via the QDs and finally to the IO-TiO2 electrode. The resulting anodic photocurrent can be modulated by the potential, the excitation intensity, and the glucose concentration, providing a new degree...

We report the fabrication of an amperometric NADH biosensor system that employs an allosterically modulated bacterial reductase in an adapted osmium(III)-complex-modified redox polymer film for analyte quantification. Chains of complexed Os(III) centers along matrix polymer strings make electrical connection between the immobilized redox protein and a graphite electrode disc, transducing enzymatic oxidation of NADH into a biosensor current. Sustainable anodic signaling required (1) a redox polymer with a formal potential that matched the redox switch of the embedded reductase and avoided interfering redox interactions and (2) formation of a cross-linked enzyme/polymer film for stable biocatalyst entrapment. The activity of the chosen reductase is enhanced upon binding of an effector, i.e. p-hydroxy-phenylacetic acid ( p-HPA), allowing the acceleration of the substrate conversion rate on the sensor surface by in situ addition or preincubation with p-HPA. Acceleration of NADH oxidation amplified the response of the biosensor, with a 1.5-fold increase in the sensitivity of analyte detection, compared to operation without the allosteric modulator. Repetitive quantitative testing of solutions of known NADH concentration verified the performance in terms of reliability and analyte recovery. We herewith established the use of allosteric enzyme modulation and redox polymer-based enzyme electrode wiring for substrate biosensing, a concept that may be applicable to other allosteric enzymes.

Redox polymer/protein biophotoelectrochemistry was used to analyse forward electron transfer of isolated PSII complexes with natural PsbA-variants. PsbA1- or PsbA3-PSII was embedded in a redox hydrogel that allows diffusion-free electron transfer to the electrode surface and thus measurement of an immediate photocurrent response. The initial photocurrent density of the electrode is up to ~2-fold higher with PsbA1-PSII under all tested light conditions, the most prominent under high-light [2,300 μmol(photon) m–2 s–1] illumination with 5 μA cm–2 for PsbA3-PSII and 9.5 μA cm–2 for PsbA1-PSII. This indicates more efficient electron transfer in low-light-adapted PsbA1-PSII. In contrast, the photocurrent decays faster in PsbA1-PSII under all tested light conditions, which suggests increased stability of high-light-adapted PsbA3-PSII. These results confirm and extend previous observations that PsbA3-PSII has increased P680+•/QA–• charge recombination and thus less efficient photon-to-charge conversion, whereas PsbA1-PSII is optimised for efficient electron transfer with limited stability.

Redox polymers are widely applied in bioelectrochemical applications. Thus, the design of novel polymers and tuning of mediator properties, in particular the redox potential, plays a crucial role for the fabrication of highly efficient bioelectrodes. This review summarizes recent developments and advances in redox polymers that were used for the development of various bioelectrochemical devices, i.e. amperometric biosensors, bioelectrocatalysis and energy conversion/storage systems.

We report on the fabrication of bioanodes for H2 oxidation based on [NiFeSe] hydrogenase. The enzyme was electrically wired by means of a specifically designed low-potential viologen-modified polymer, which delivers benchmark H2 oxidizing currents even under deactivating conditions owing to efficient protection against O2 combined with a viologen-induced reactivation of the O2 inhibited enzyme. Moreover, the viologen-modified polymer allows for electrochemical co-deposition of polymer and biocatalyst and, by this, for control of the film thickness. Protection and reactivation of the enzyme was demonstrated in thick and thin reaction layers.

An intrinsic self-charging biosupercapacitor built on a unique concept for the fabrication of biodevices based on redox polymers is presented. The biosupercapacitor consists of a high-potential redox polymer based bioanode and a low-potential redox polymer based biocathode in which the potentials of the electrodes in the discharged state show an apparent potential mismatch E

Novel [15]crown-5 and [18]crown-6 o-terphenyls differing in number and position of sulfur in the side chains and their corresponding triphenylene analogues were synthesized via a nucleophilic aromatic displacement of fluoride as the key step. Except for one short chain derivative all other compounds showed enantiotropic columnar mesophases which were studied by DSC, POM and XRD (WAXS, SAXS). The presence of sulfur induced broad room temperature columnar mesophases. This effect was more pronounced for bend [15]crown-5 derivatives than for linear [18]crown-6 derivatives. Redox properties were mostly governed by the triphenylene moieties, showing stepwise oxidation of the individual triphenylene units.

If the analyte does not only change the electrochemical but also the optical properties of the electrode/solution interface, the spatial resolution of an electrochemical sensor can be substantially enhanced by combining the electrochemical sensor with optical microscopy. In order to demonstrate this, electrochemical biosensors for the detection of hydrogen peroxide and glucose were developed by drop casting enzyme and redox polymer mixtures onto planar, optically transparent electrodes. These biosensors generate current signals proportional to the analyte concentration via a reaction sequence which ultimately changes the oxidation state of the redox polymer. Images of the interface of these biosensors were acquired using bright field reflected light microscopy (BFRLM). Analysis showed that the intensity of these images is higher when the redox polymer is oxidized than when it is reduced. It also revealed that the time needed for the redox polymer to change oxidation state can be assayed optically and is dependent on the concentration of the analyte. By combining the biosensor for hydrogen peroxide detection with BFRLM, it was possible to determine hydrogen peroxide in concentrations as low as 12.5 µM with a spatial resolution of 12 µm × 12 µm, without the need for the fabrication of microelectrodes of these dimensions.

International audience; We report the fabrication of a polymer/enzyme based biosupercapacitor (BSC)/biofuel cell (BFC) hybrid device with optimized cell voltage that can be switched on demand from energy conversion to energy storage mode. The redox polymer matrices used for the immobilization of the biocatalyst at the bioanode and biocathode act simultaneously as electron relays between the integrated redox enzymes and the electrode surface (BFC) and as pseudo-capacitive charge storing elements (BSC). Moreover, due to the self-charging effect based on the continuously proceeding enzy-matic reaction, a Nernstian-shift in the pseudo-capacitive elements, i.e. in the redox polymers, at the individual bioelectrodes leads to a maximized open circuit voltage of the device in both operating modes. Comparison with a conventional fuel cell design, i.e. using redox mediators with redox potentials that are close to the potentials of the used redox proteins, indicates that the novel hybrid device shows a similar voltage output. Moreover, our results demonstrate that the conventional design criteria commonly used for the development of redox polymers for the use in biofuel cells have to be extended by considering the effect of a Nernstian-shift towards the potentials of the used biocatalysts in those pseudo-capacitive elements.