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Nanoconfinement of enzymes in nanocage-structured electrodes for bioelectrocatalytic energy conversion – CAGEZYMES

Nanocage electrodes to confine and protect fragile enzymes for sustainable energy conversion

Enzymes have advantages compared to synthetic or rare metal catalysts such as exquisite specificity and reactivity under mild conditions, but they are complex and fragile. The limited stability of enzyme bioelectrodes is a technological bottleneck for next generation biofuel cells and biosensor devices.

Enzyme nanoconfinement in porous nanocage structures to enhance the stability and activity of bioelectrocatalytic reactions, and leading to new understanding of enzyme reactivity in porous materials

Enzymes are nature’s catalysts that drive many important biological reactions. Compared to synthetic or rare metal catalysts, enzymes have advantages such as exquisite specificity, high reactivity under mild conditions, and low environmental impact. However, the fragility of enzymes outside of their environment is a major issue that limits or restricts their widespread use. Enzymatic biofuel cells are a sub category of fuel cells that can deliver µW to mW cm-2 power outputs from natural fuels such as glucose and oxygen. Biofuel cells now offer the real prospect of replacing miniaturised batteries that are complex and non-ecological. A commonly overlooked issue and important technological bottleneck is the limited stability of enzymes and enzyme-electrode interfaces, particularly under challenging and deactivating conditions. This issue not only applies to biofuel cells but also related enzymatic biosensor technologies where bioelectrocatalytic electrodes are core technologies.<br /><br />Recent works have demonstrated that a high level of control over the spatial confinement of enzymes at surfaces, interfaces, and in small volumes, can dramatically enhance their catalytic activity and stability compared to free enzymes in solution. Pore size engineering, with a high level of control over factors such as pore size and spatial distribution, has recently emerged for improving redox enzyme immobilisation and electrical wiring for bioelectrocatalysis. Nevertheless, the best performing porous materials are often poorly controlled. This opens up a new research avenue aimed at confining and shielding enzymes in ordered porous architectures.<br /><br />The main goal is develop ultra-precise nanocage-structured electrodes to confine and protect fragile redox enzymes to extend the lifetime of biofuel cells for a more sustainable energy future. The vision is to develop new methodology and understanding that will apply to enzymes for energy conversion. It is envisaged that the nanocage concept and/or nanocage materials can be later extended to other fragile catalysts or entities for a spring-board of applications from fuel cells to supercapacitors to sensors.

Methods will be developed to elaborate metal organic framework (MOF) electrodes with specific properties including pore structures, chemical functions, and conductivities. Innovative MOF electrode assembly methods are being elaborated. Electrochemistry, powder-x ray diffraction, electron microscopy, and spectroscopic techniques are the principal characterisation techniques used in this project.

In the first half of this project we made good progress on the synthesis and characterisation of micro- and meso-porous MOFs and MOF-derived electrodes integrating carbon nanotubes. Solvothermal and hydrothermal synthesis methods of water-stable MOFs such as ZIF-8 and MIL(100) MOFs have been developed. The synthesis of a redox-active mesoporous MOF that exploits ferrocene as a redox mediator for the electrical wiring of enzymes is well underway. Composite and layer-by-layer strategies have been developed and insight into solvent effects on film and electrode stability revealed. Further experiments are planned to improve control and uniformity of MOF layers. The first conductive MOF materials have been developed but no electrochemistry has been performed; product quantities are very small (scale up required).

Important progress has been made on the assembly and characterisation of MOF/enzyme composites (WP 2) for biocatalysis and bioelectrocatalysis. We have developed post-synthetic assembly methods at this point but in-situ enzyme encapsulation is also planned. We have explored activities with metalloenzymes for oxygen and H202 reduction (e.g. for enzymatic biocathodes).

The possibility to achieve electron transfer between immobilised redox enzymes at MOF bioelectrodes has been achieved in physiological buffer. Thorough stability tests have been performed. For example, tests have been explored in the presence of inhibitors and/or interfering agents. Somewhat unexpectedly, we show that the MOF and the ligand are both effective in improving bioelectrocatalytic reduction reactions in the presence and absence of inhibitors and interfering agents. We have some evidence of nanocaging and electrostatic protection effects but further experiments and understanding are necessary.

This project focusses on advancing the field of bioelectrocatalysis and particularly the development of improved (longer-lasting) catalytic electrodes and biofuel cells under challenging conditions for clean and sustainable energy. This project is making important advances in the domains of nanoscale surface chemistry, porous materials science, biology, and electrochemistry. As mentioned earlier, the methodology developed could be extended for confinement of other catalysts or entities for applications including fuel cells, sensors and reactors.

Enzymatic biofuel cells with typical µW to mW power outputs are currently destined for low-power applications, for example, for the powering of electronic medical devices. Miniaturised battery recycling is ineffective and ultimately leads to problems such as environmental pollution. Socially, there is an ever-increasing demand for wearable and implantable medical devices, for example, for personal health monitoring. This CAGEZYMES project is destined to deliver new fundamental results and understanding to help prolong the lifetime and enhance the performance of bioelectrocatalytic electrodes for applications in biofuel cells as well as biosensors.

The development of porous materials and sustainable catalysis for clean energy conversion in this project is aligned with the European Union climate and energy strategy including EU directives to develop clean energy for Europeans with improved use of renewable materials and energy.

2 publications to date.

Enzymes are nature's catalysts that are being increasingly exploited at electrodes for studying and controlling chemical transformations. Enzymes have advantages compared to synthetic catalysts such as exquisite specificity but they are complex and fragile. The project aim is to develop molecularly-precise nanocage structures for confinement and protection of fragile redox enzymes for bioelectrocatalysis. Methods will be developed to obtain metal organic framework (MOF) electrodes with specific pore structures and chemistry. New knowledge in MOF synthesis and breakthrough methods in MOF-electrode assembly will be developed. The project will reveal if nanocage structures can stabilise enzymes, lead to new understanding of enzyme function, and result in next generation biofuel cells for sustainable energy conversion. This 4-year project will allow the esteemed junior CNRS researcher to build his research team and lead the development of a new thematic and its sub-topics in Grenoble.

Project coordination


The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.



Help of the ANR 179,550 euros
Beginning and duration of the scientific project: September 2020 - 48 Months

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