DOI: 10.1002/celc.201300148 Photoelectrochemical Communication between Thylakoid Membranes and Gold Electrodes through Different Quinone Derivatives Kamrul Hasan, [a] Yusuf Dilgin, [b] Sinan Cem Emek, [a] Mojtaba Tavahodi, [c] Hans-Erik kerlund, [a] Per-ke Albertsson, [a] and Lo Gorton* [a] 1. Introduction The viable production of solar fuels through photochemical energy conversion is a promising resource that can offer long- standing global energy. Nature has optimized photosynthesis, its own solar energy-conversion system, to a finely tuned mo- lecular mechanism. [1] Photosynthesis is the sustainable, effi- cient, and complex process that converts light energy into chemical energy. [2] Thylakoid membranes, photosynthetic sub- cellular organelles, are found in cyanobacteria and in plant chloroplasts. Thylakoids contain the photosynthetic apparatus that is composed of two photosystems, photosystem I (PS I) and photosystem II (PS II), and other necessary components, such as enzymes and cofactors, as outlined in Scheme 1. The photosynthetic reaction starts from the photoexcitation of PS II by light, which results in the oxidation of water into O 2 . The electrons produced from this reaction are transferred through a series of electron carriers, for example plastoquinone (PQ), cytochrome b 6 f, and plastocyanin (PC), to PS I, in which they are excited once more. [3] Excitation of PS I results in the trans- fer of the electrons, causes them to reduce the terminal elec- tron-acceptor ferredoxin (Fd), and subsequently produces re- duced nicotinamide adenine dinucleotide phosphate (NADPH), which is used in the Calvin cycle for fixation of CO 2 to produce sugars. [4] The proton gradient, resulting from the photosynthet- ic reactions, is used by adenosine triphosphate (ATP) synthase to produce ATP, which is the ultimate cellular energy curren- cy. [3] The quantum yield in the thylakoid membrane is nearly 100 %, which makes it very attractive for photobioelectrochem- ical systems. [5] In recent years, extensive research has been focused on pho- toelectrochemical and artificial solar cells imitating photosyn- thesis for energy production. [6–10] Isolated photosynthetic reac- tion centers, especially PS I, have been wired to electrodes to produce hydrogen as a feasible energy source. [1, 11–13] Isolated PS I has previously been wired to a gold electrode by using an osmium-containing redox polymer and methyl viologen as a final electron acceptor, which generated a photocurrent den- sity of 29 mA cm À2 . [14] To take advantage of natural photosyn- thesis, several research groups have devoted their efforts on photobioelectrochemical systems that are based on chloro- plasts, [15] thylakoid membranes, [16–19] photosynthetic reaction centers, [2, 20–27] and bacterial cells. [28–31] However, low electron- transfer efficiency from the photosynthetic machinery to the electrode has confined the performance of these types of sys- tems. Isolated photosynthetic components have some benefits over the entire cell/membrane. For instance, they do not have respiration competing with the photosynthetic electron-trans- fer pathways and they do not require any nutrients for their growth to continue. However, they suffer from low compe- tence because of their inadequate stability on an electrode sur- face. It might be that proper immobilization and good electri- Photosynthesis is a sustainable process for the conversion of light energy into chemical energy. Thylakoids in energy-trans- ducing photosynthetic membranes are unique in biological membranes because of their distinguished structure and com- position. The quantum trapping efficiency of thylakoid mem- branes is appealing in photobioelectrochemical research. In this study, thylakoid membranes extracted from spinach are shown to communicate with a gold-nanoparticle-modified solid gold electrode (AuNP–Au) through a series of quinone derivatives. Among these, para-benzoquinone (PBQ) is found to be the best soluble electron-transfer mediator, generating the highest photocurrent of approximately 130 mAcm À2 from water oxidation under illumination. In addition, the photocur- rent density is investigated as a function of applied potential, the effect of light intensity, quinone concentration, and amount of thylakoid membrane. Finally, the source of photo- current is confirmed by using 3-(3,4-dichlorophenyl)-1,1-dime- thylurea (known by its trade name, Diuron), an inhibitor of photosystem II, which decreases the total photocurrent by 50 %. [a] K. Hasan, Dr. S. C. Emek, Prof. H.-E. kerlund, Prof. P.-. Albertsson, Prof. L. Gorton Biochemistry and Structural Biology, Lund University P.O. Box 124, SE-22100, Lund (Sweden) E-mail: Lo.Gorton@biochemistry.lu.se [b] Prof. Y. Dilgin Science & Art Faculty, Department of Chemistry C¸anakkale Onsekiz Mart University, C¸anakkale (Turkey) [c] M. Tavahodi Department of Chemistry Institute of Advanced Studies in Basic Sciences, Zanjan (Iran) Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/celc.201300148. # 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemElectroChem 2014, 1, 131 – 139 131 CHEMELECTROCHEM ARTICLES