Carbon dots as versatile photosensitizers for solar-driven catalysis with redox enzymes

Georgina A. M. Hutton, Bertrand Reuillard, Benjamin C. M. Martindale, Christine A. Caputo, Colin W. J. Lockwood, Julea N. Butt, Erwin Reisner

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Light-driven enzymatic catalysis is enabled by the productive coupling of an enzyme to a photosensitizer. Photosensitizers used in such hybrid systems are typically costly, toxic and/or fragile, with limited chemical versatility. Carbon dots (CDs) are low-cost nano-sized light-harvesters that are attractive photosensitizers for biological systems as they are water-soluble, photostable, non-toxic and their surface chemistry can be easily modified. We demonstrate here that CDs act as excellent photosensitizers in two semi-biological photosynthetic systems utilizing either a fumarate reductase (FccA) for the solar-driven hydrogenation of fumarate to succinate, or a hydrogenase (H2ase) for reduction of protons to H2. The tunable surface chemistry of the CDs was exploited to synthesize positively charged ammonium-terminated CDs (CD-NHMe2+), which were capable of transferring photo-excited electrons directly to the negatively charged enzymes with high efficiency over 24 h. Enzyme-based turnover numbers of 6000 mol succinate (mol FccA)−1 and 43 000 mol H2 (mol H2ase)−1 were reached after 24 h. Negatively charged carboxylate-terminated CDs (CD-CO2) displayed little or no activity and the electrostatic interactions at the CD–enzyme interface were determined to be essential to the high photocatalytic activity observed with CD-NHMe2+. The modular surface chemistry of CDs together with their photo-stability and aqueous solubility make CDs versatile photosensitizers for redox enzymes with tremendous scope for their utilization in photobiocatalysis.
Original languageEnglish
Pages (from-to)16722–16730
Number of pages9
JournalJournal of the American Chemical Society
Issue number51
Early online date28 Nov 2016
Publication statusPublished - 28 Dec 2016

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