Adrian Ruff

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.

Enzymatic hydrolysis of lignocellulosic biomass for biofuel production relies on complex multi-enzyme ensembles. Continuous and accurate measurement of the released key products is crucial in optimizing the industrial degradation process and also investigating the activity and interaction between the involved enzymes and the insoluble substrate. Amperometric biosensors have been applied to perform continuous cellobiose measurements during the enzymatic hydrolysis of pure cellulose powders. The oxygen-sensitive mediators used in these biosensors restricted their function under physiological or industrial conditions. Also, the combined measurements of the hydrolysis products cellobiose and glucose require a high selectivity of the biorecognition elements. We employed an [Os(2,2′-bipyridine)₂Cl]Cl-modified polymer and cellobiose dehydrogenase to fabricate a cellobiose biosensor, which can accurately and specifically detect cellobiose even in the presence of oxygen and the other main product glucose. Additionally, a glucose biosensor was fabricated to simultaneously measure glucose produced from cellobiose by β-glucosidases. The cellobiose and glucose biosensors work at applied potentials of +0.25 and +0.45 V versus Ag|AgCl (3 M KCl), respectively, and can selectively detect their substrate. Both biosensors were used in combination to monitor the hydrolysis of pure cellulose of low crystallinity or industrial corncob samples. The obtained results correlate with the high-performance liquid chromatography pulsed amperometric detection analysis and demonstrate that neither oxygen nor the presence of redox-active compounds from the lignin fraction of the corncob interferes with the measurements.

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.

We report on a photobioelectrochemical fuel cell consisting of a glucose‐oxidase‐modified BiFeO₃photobiocathode and a quantum‐dot‐sensitized inverse opal TiO₂photobioanode 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.

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.

Eine definierte Assemblierung von photosynthetischen Proteinkomplexen ist für eine optimale Leistung von semiartifiziellen Energieumwandlungssystemen erforderlich, die in der Lage sind, einen unidirektionalen Elektronenfluss zu liefern, wenn lichtsammelnde Proteine mit Elektrodenoberflächen verbunden werden. Wir stellen gemischte Photosystem‐I (PSI)‐Monoschichten vor, die aus nativen cyanobakteriellen PSI‐Trimeren in Kombination mit isolierten PSI‐Monomeren aus demselben Organismus bestehen. Die sich daraus ergebende kompakte Anordnung gewährleistet eine hohe Dichte an photoaktiven Proteinkomplexen pro Flächeneinheit und bildet die Grundlage für eine wirksame Minimierung von Kurzschlussprozessen, die die Leistung von PSI‐basierten Bioelektroden typischerweise einschränken. Die PSI‐Schicht ist darüber hinaus mit Redoxpolymeren für einen optimalen Elektronentransfer verbunden, was eine hocheffiziente lichtinduzierte Photostromerzeugung ermöglicht. Die Kopplung der Photokathode mit einer [NiFeSe]‐Hydrogenase ermöglicht lichtinduzierte H₂‐Entwicklung.

We report on a photobioelectrochemical fuel cell consisting of a glucose‐oxidase‐modified BiFeO₃photobiocathode and a quantum‐dot‐sensitized inverse opal TiO₂photobioanode 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.

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.

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 NH₃ nmol MoFe⁻¹ h⁻¹ durch N₂‐Reduktion. Die biosynthetische N₂‐Reduktion zu NH₃ wurde durch ¹⁵N₂‐Markierungsexperimente und NMR‐Analysen bestätigt.

Die Verwendung hochaktiver, aber zeitgleich auch hochempfindlicher Katalysatoren (z. B. [FeFe]‐Hydrogenase aus Desulfovibrio desulfuricans) in Biobrennstoffzellen ist nach wie vor eine der größten Herausforderungen bei der nachhaltigen Energieumwandlung. Wir berichten über die Herstellung einer auf Gasdiffusionselektroden‐basierten H₂ /O₂‐Biobrennstoffzelle, die mit einer [FeFe]‐Hydrogenase/Redoxpolymer‐basierten H₂‐Oxidationsbioanode mit hoher Stromdichte ausgestattet ist. Die Bioanoden zeigen Benchmark‐Stromdichten von ca. 14 mA cm⁻², und die entsprechenden Brennstoffzellentests zeigen einen Benchmark für eine Polymer/Hydrogenase‐basierte Biobrennstoffzelle mit herausragenden Leistungsdichten von 5.4 mW cm⁻² bei 0.7 V Zellspannung. Darüber hinaus wird die hochempfindliche [FeFe]‐Hydrogenase durch das Redoxpolymer vor Sauerstoffschäden geschützt und kann unter 5 % O₂ arbeiten.