Marc Riedel

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 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.

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.

Triggering electrochemical reactions with light provides a powerful tool for the control of complex reaction schemes on photoactive electrodes. Here, we report on the light-directed, multiplexed detection of enzymatic substrates using a non-structured gold electrode modified with CdSe/ZnS quantum dots (QDs) and two enzymes, i.e. glucose oxidase (GOx) and sarcosine oxidase (SOx). While the QDs introduce visible light-sensitivity into the electrode architecture, GOx and SOx allow for a selective conversion of glucose and sarcosine, respectively. For the QD immobilization to the gold electrode a linker-assisted approach using trans-4,4’-stilbenedithiol (StDT) has been used, resulting in a generation of a photocurrent. Subsequently, GOx and SOx have been immobilized in spatially separated spots onto the QD electrode. For the local read-out of the QD electrode a new measurement set-up has been developed by moving a laser pointer across the surface to defined positions on the chip surface. The amplitudes of the photocurrents upon illumination of the GOx or SOx spot depend in a concentration-dependent manner on the presence of glucose and sarcosine, respectively. This measurement also allows for a selective detection in the presence of the other substance. The set-up demonstrates the feasibility of multiplexed measurements of enzymatic reactions using a focused light pointer resulting in an illumination area with a diameter of 0.3 mm for analyzing spots of different enzymes. Moving the laser pointer in x- and y-direction and simultaneously detecting the local photocurrent also allows a spatial imaging of enzyme immobilisation and activity distribution. Here not only the spot dimensions, but also the activity of the enzyme can be verified.

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 (P_Os), 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 P_Os 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 H₂O/O₂ photobioelectrochemical cell reaching a high open‐circuit voltage of about 1 V under illumination.

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 (P_Os), 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 P_Os 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 H₂O/O₂ photobioelectrochemical cell reaching a high open‐circuit voltage of about 1 V under illumination.

Inspired by natural photosynthesis, coupling of artificial light-sensitive entities with biocatalysts in a biohybrid format can result in advanced photobioelectronic systems. Herein, we report on the integration of sulfonated polyanilines (PMSA1) and PQQ glucose dehydrogenase (PQQ-GDH) into inverse opal TiO2 (IO-TiO2) electrodes. While PMSA1 introduces sensitivity for visible light into the biohybrid architecture and ensures the efficient wiring between the IO-TiO2 electrode and the biocatalytic entity, PQQ-GDH provides the catalytic activity for the glucose oxidation and therefore feeds the light-driven reaction with electrons for an enhanced light-to-current conversion. Here, the IO-TiO2 electrodes with pores of around 650 nm provide a suitable interface and morphology, needed for the stable and functional assembly of polymer and enzyme. The IO-TiO2 electrodes have been prepared by a template approach applying spin coating, allowing an easy scalability of the electrode height and surface area. The successful integration of the polymer and the enzyme is confirmed by the generation of an anodic photocurrent, showing an enhanced magnitude with increasing glucose concentrations. Compared to flat and nanostructured TiO2 electrodes the 3-layered IO-TiO2 electrodes give access to a 24-fold and 29-fold higher glucose-dependent photocurrent due to the higher polymer and enzyme loading in IO-films. The three dimensional IO-TiO2|PMSA1|PQQ-GDH architecture reaches maximum photocurrent densities of 44.7 ± 6.5 µA cm-2 at low potentials in the presence of glucose (for a 3 TiO2 layer arrangement). The onset potential for the light-driven substrate oxidation is found to be at -0.315 V vs. Ag/AgCl (1 M KCl) under illumination with 100 mW cm-2, which is more negative than the redox potential of the enzyme. The results demonstrate the advantageous properties of IO-TiO2|PMSA1|PQQ-GDH biohybrid architectures for the light-driven glucose conversion with improved performance.