Research

This research topic targets a novel sensing approach for sparing the fossil energy resources massively used in agriculture. The production of nitrogen fertilizer alone consumes up to 5% of the global natural gas production. These fertilizers are applied in excess in the field and lost in the form of nitrates. Our group addresses this issue by developing sensors to determine the nitrate content in plants directly in the field by the farmers themselves to provide the information on the plants’ need to adjust the fertilizer input in real-time¹. The democratization of the use of such sensors requires simple procedures for on-site nitrate quantification without sample preparation. To this end a redox enzyme that selectively reduces nitrate² is contacted via artificial electron relays to single-use electrodes. The main interferences in this sensing concept when brought from the lab to field applications is oxygen from air. To overcome this issue, we develop universal oxygen scavengers that are compatible with biochemical and electrochemical processes. The principal challenge resides in designing an oxygen reduction reaction that results in fully inert products³. Enzymatic oxygen scavengers based on carbohydrate oxidation are most promising and we selected the enzymes catalase and pyranose oxidase to reduce oxygen with glucose to water. Such O₂ scavenging systems maintain tiny volumes (down to 20 µL) under anaerobic conditions for hours, even when exposed to ambient air. The conditions of the systems such as pH value or biological activity are not affected by the oxygen reduction product^4,5. We demonstrated that the oxygen scavenger system associated to the nitrate biosensing concept allow for fast, simple and reliable nitrate quantification on the field.
The impact of the nitrate biosensing method to spare fossil ressources and to eventually reduce CO₂ emission was recently recognized by KlimaExpo.NRW who made it a priority topic to encourage and educate about climate protection⁶. The method is awaiting validation of a pending patent application⁷.

1. Plumeré N. Nachrichten aus der Chemie 2014, 62(7), 777-779.  DOI: 10.1002/nadc.201490261
2. Campbell W. H., Henig J., Plumeré N. Bioelectrochemistry, 2013, 93, 46-50.  DOI: 10.1016/j.bioelechem.2012.07.002
3. Plumeré N. Analytical and Bioanalytical Chemistry, 2013, 405(11), 3731-3738.  DOI: 10.1007/s00216-013-6827-z
4. Swoboda M., Henig J., Cheng H.-M., Brugger D., Haltrich D., Plumeré N., Schlierf M. ACS Nano, 2012, 6(7), 6364-6369.DOI: 10.1021/nn301895c
5. Plumeré N., Henig J. and Campbell W. H. Analytical Chemistry, 2012, 84, 2141-2146.  DOI: 10.1021/ac2020883
6. Plumeré N.,Nitratsensor: Schluss mit Überdüngung – Feldanalytik in der Landwirtschaft. KlimaExpo.NRW Motor für den Fortschritt
7. Plumeré N., Campbell W. H., Campbell E. R., Systems and Methods for Enzymatic Oxygen Removal.  US2012211372 (A1) – 2012-08-23

Besides organic and inorganic semiconductors, that have reached practical efficiencies and commercial applications, the utilization of photosynthetic material in artificial device to convert light energy is principally demonstrated¹. Currently there is a growing recognition of the applicability of the biological machinery of photosynthesis as the active solar cell material. The primary advantage being that these molecular systems have been already optimized for light harvesting and charge separation by over 3 billion years of evolution. In theory the use of photosynthetic proteins may result in biophotovoltaic devices with open circuit voltages in excess of 1 V and non-limiting electron transfer rates¹. The utilization of photosynthetic proteins as solar cell material may ultimately provide the cheapest possible photovoltaics devices since these key building blocks can be harvested from organisms such as algae in large scales. Biophotoelectrode designed for photovoltaics may also be applied for chemical fuel production² and for novel sensing concepts.
To these ends, we design redox hydrogels for highly efficient electrical contacting and stabilization of the natural photosynthetic protein in artificial devices. While early devices yielded only low efficiency³, the fine tuning of electron mediators with redox potentials adjusted to the one of the protein resulted in several order of magnitude improvement in both photocurrents⁴ and voltages⁵. Together with our cooperation partners (W. Schuhmann, M. Nowaczyk and M. Rögner), we have shown that electrons provided by photosynthetic proteins can be recovered at artificial conducting materials, even faster than in natural photosynthesis itself⁴. The possibility to further improve these performances raise the expectation to eventually achieve practical efficiency from biophotovoltaic devices to provide electrical energy both in high tech devices, such as biocompatible photovoltaics in smart contact lenses⁶, and in low tech, “painted” large scale solar cells which opens new routes for the cost-per-Watt race in electrical energy production⁷.

1. Plumeré, N. Nature Na notech. 2012, 7 (10), 616–617.  DOI: 10.1038/nnano.2012.175
2. Zhao F., Conzuelo F., Hartmann V., Li H., Nowaczyk M. M., Plumeré N., Rögner M., Schuhmann W., J. Phys. Chem. B, 2015, 119 (43), 13726–13731.  DOI: 10.1021/acs.jpcb.5b03511
3. Kothe, T.; Plumeré, N.; Badura, A.; Nowaczyk, M. M.; Guschin, D. A.; Rögner, M.; Schuhmann, W., Angew. Chem. Int. Ed. 2013, 52 (52), 14233–14236.  DOI: 10.1002/anie.201303671
4. Kothe T., S. Pöller, F. Zhao, P. Fortgang, M. Rögner, W. Schuhmann, N. Plumeré Chemistry – A European Journal, 2014, 20, 11029–11034. DOI: 10.1002/chem.201402585
5. Hartmann V.,Kothe T., Pöller S., El-Mohsnawy E., Nowaczyk M. M., Plumeré N., Schuhmann W.,Rögner M., Phys. Chem. Chem. Phys., 2014, 16, 11936-11941.  DOI: 10.1039/C4CP00380B
6. Ravilious K, Clothes that recharge your laptop – the near-endless possibilities of artificial leaves. Horizon, The research & innovation magazine of the European commission. 16 October 2014
7. Plumeré et al., Researchers forecast an Ebola vaccine and low-cost solar cells in 2015. Horizon, The research & innovation magazine of the European commission, 5 January 2015

We use organic chemistry, molecular biology and electrochemical approaches to build biologic-organic hybrid architectures. We are working on the development of nanosized chelators to achieve the specific recognition and orientation of a redox protein. Our interest is to gain fundamental information on the chelate effect on the supramolecular level. Understanding and adjusting the molecular recognition between the receptor and the guest in combination to designing electron relays to bridge redox enzymes are the key issues to achieve controlled orientation and fast electron transfer. We apply our redox protein immobilization concepts for sensing (nitrate biosensors) and energy conversion applications (bio-photovoltaics and bio-fuel cells).