The purpose of this study was to use a photosynthetic antenna complex (LH) assembled on substrates for the development of nanobiodevices from solar to fuel. We use the LH to construct an efficient energy transfer system for nanobiodevices and nanobiomaterial applications. In this study, we primarily aimed to construct an array of photosynthetic antennae on substrates using a modified photosynthetic antenna complex prepared from modern biosynthetic manufacturing methods and in lipid membranes.
C- or N- terminal His-tagged RC-LH1s from Rhodobacter (Rb.) sphaeroides were engineered and attached to Ni-NTA-assembled substrates to assess their orientation and electric contact with the substrates. Point-contact current imaging AFM was used to determine their topography and current/voltage characteristics. The photocurrent responses of the C- or N-His RC-LH1 complexes on the gold electrodes modified with SAM (Ni-NTA and alkanethiol (1-decanethiol, C₁₀SH)) were measure when these electrodes were illuminated. These results indicate that one-way electron transfer from pigments in the RC-LH1 complex to methyl viologen (MV) occurred. The photocurrent density, normalized by RC-LH1 adsorbed, was greater for C-His RC-LH1than N-His RC-LH1. The magnitude of the photocurrent was, therefore, very sensitive to the orientation of RC-LH1 complexes on the modified gold electrode. An AFM topography image was recorded under ambient (N2) conditions of C-His LH1-RCs adsorbed onto the Ni-NTA substrate using an Au/Ir-coated Si probe. Current-voltage measurements showed a semiconducting I-V curve that shows a reversed rectification direction relative to those of C-His RC-LH1s. These results show that His tags fused to the C or N termini of the RC-LH1s can control the orientation of the transmembrane protein complexes assembled on the substrate.
Further,the electron conductivity and photocurrent of the RC-LH1 complex embedded in a lipid membrane were measured using C-AFM and photoelectrochemical analyses. AFM topography showed that RC-LH1 molecules were well oriented with their H-subunits toward the membrane surface. RC-LH1 embedded in a membrane-generated photocurrent upon irradiation when assembled on an electrode. The observed action spectrum was consistent with the absorption spectrum of RC-LH1. The control of the orientation of RC-LH1 by lipid membranes provided well-defined conductivity and photocurrent.
These methods of using self-assembly of photosynthetic protein complexes to study electron transfer reactions of LH on electrodes are promising for the development of nanobiodevices and nanobiomaterials from solar to fuel. Based on biological design principles, future biology-based or synthetic organic photonics could potentially provide clean and inexpensive energy alternatives.

Photosystem I (PSI) is a ~10 nm protein complex that drives photosynthesis. Because of its nanoscale size and photodiode-like properties, PSI has drawn a surging interest for use in biologically inspired energy conversion devices upon extracting it from plants and assembling it as films on electrode surfaces. The research described in this presentation will focus on the molecular and electronic integration of spinach-extracted PSI at electrode surfaces, including metals, rectifying semiconductors, graphene, and conducting polymers to produce both “wet” photoelectrochemical cells and solid-state devices. In both areas, thicker films of PSI, prepared by simple drop casting, absorb more light and yield much greater photocurrents as compared to monolayer films. The electrode that these films are deposited on is vitally important for the performance of the film. For example, micron-thick PSI films on p-doped silicon produce 200-times greater photocurrents than those obtained by deposition on gold. The position of the Fermi level combined with the band gap of silicon enables unidirectional electron transfer to PSI so that current cancellation from non-optimally aligned proteins is avoided. Furthermore, fabricating a composite film that contains both PSI and graphene oxide improves film structure and conductivity and enhances the observed photocurrents. Recent efforts are exploring solid-state PSI systems by contacting the protein with conducting polymers, including polyaniline and polythiophenes, via both electrodeposition and surface-initiated routes. These research efforts are leading to vastly improved performances for PSI-biohybrid solar cells.

Great interest has been given to photosynthetic systems for their potential in future technological applications such as bio-sensors and bio-solar cells. In this context, previous studies have focused on depositing photosynthetic proteins from plants and bacteria onto conducting surfaces. In order to make surface adhered protein complexes viable for applications some basic issues need to be addressed, such as, the efficiency of electron transfer between the electrode and the protein and the orientation of these complexes on the electrode. In this respect, photocurrent measurements on an atomically flat electrode in combination with a monolayer of photosynthetic complexes provides a well-defined system. Here we report the Langmuir-Blodgett deposition technique as a promising method to create self assembled monolayers of isolated photosynthetic proteins with uniform orientation and minimal distance between the proteins and surface. We assessed the properties of this system by means of photo-electrochemistry and show to be able to orient the photosynthetic complexes with 90% accuracy. This system produces a peak photocurrent density of 43 µA/cm² and steady state photocurrent density of 23 µA/cm² with corresponding internal and external quantum efficiencies of 32% and 0.27% for the peak, and 16% and 0.18%, for the steady state. This represents the largest photocurrent for a single monoloyer reported to date.

Photoactive reaction centers (RCs) are protein complexes in bacteria which can convert sunlight into other forms of energy with a high internal efficiency. The photo-stimulation of immobilized RCs on inorganic electrodes can result in the generation of photocurrent that is of interest for bio-solar cell applications.
However, to retain their functionality, the photoactive proteins have to be surrounded by a suitable environment, which implies a proper selection of the electrode material. In this contribution, we investigate the potential of diamond and graphene electrodes to realize biohybrid systems based on bacterial reaction centers from purple bacteria immobilized on these materials.
We will discuss functionalization methods, involving self-assembled monolayers and polymer brushes, aiming at preparing a suitable environment for grafting molecules and proteins onto diamond and graphene surfaces. In particular, we have investigated the effect of the surface functionalization with the linker-molecule 6-phosphonohexanoic acid and with the polymer polymethacrylic acid on the photocurrent generation and the stability of biohybrid systems based on nanocrystalline diamond and graphene electrodes.
We have studied and optimized the photoresponse based on chronoamperometry experiments in the presence of different electron mediators like the coenzyme Q₀, the protein cytochrome c, and the redox molecule aminomethylferrocene. A deeper insight into the mechanism of the photocurrent generation with respect to the coexisting different charge transfer processes will be presented.

Photosystem I is one of two photosynthetic reaction centers, Photosystem I (PSI) and Photosystem II (PSII) involved in oxygenic photosynthesis. This mode of photosynthesis is found in all cyanobacteria, algae and plants. It involves the sequential activity of PSII and PSI to mediate the splitting of water and the ultimate reduction of Fd. The ability to use water as the ultimate electron donor makes this process very attractive for potential direct solar conversion without the need for plant growth and biomass production. Unfortunately, PSII is very labile and easily damaged during its photo cycle. Unlike PSII, PSI has been shown to be remarkably robust, able to function for nearly one year in energy conversion systems. In addition to this robust stability in vitro, PSI also has a much more negative potential and is able to directly product H₂. These properties as well as the unique architecture of PSI have attracted considerable research interest in the past decade worldwide. I will discuss multiple strategies, challenges, and progress is using PSI for Applied Photosynthesis. I will explore the multiple interfaces that we have used for converting solar energy into hydrogen and photocurrents. In addition, new biomolecular strategies will be discussed to possibly alleviate potential kinetic, efficiency, and stability limitations.

Bacterial photosynthetic reaction centers (RCs) are promising materials for solar energy harvesting, due to their high internal quantum efficiency and long recombination time of generated charges. In this work, photoactive electrodes were prepared from a bacterial RC-light-harvesting 1 (LH1) core complex, where the RC is encircled by the LH1 antenna, to increase light capture. A simple immobilization method was used to prepare RC-LH1 photoactive layers. The Bacterial RC-LH1s were pretreated with exogenous quinone prior to immobilization. Herein, we demonstrate that the combination of pretreatment of the RC-LH1 protein complexes and the immobilization method results in bio-photoelectrochemical cells with current response of 3.5 µA cm-2 and external quantum efficiency of 0.21%. This work provides new directions to higher performance bio-photoelectrochemical cells as well as possibly other applications of this broadly functional photoactive material.

In natural photosynthesis, light-induced high-energy electrons are transported through the chains of electron carriers located in thylakoid membranes. After a number of redox reactions, electrons are finally used for reduction of NADPH. Extraction of photosynthetic electrons before the Calvin-Benson cycle can enhance the efficiency of bioenergy harvesting. Previously, we reported the direct extraction of photosynthetic electrons using custom-built AFM-compatible nanoelectrodes from living algal cells, Chlamydomonas reinhardtii (Chalmy cells), which were trapped in microfluidic traps. Although the work demonstrated the feasibility of energy harvesting of high-energy electrons from living plant cells, there still remains multiple challenges including the identification of the source of the photosynthetic electrons. Here, we report the development of vertically-aligned nanoelectrode arrays which can be inserted into single algal cells. Using highly doped silicon-on-insulator wafers, we made electrode arrays with high aspect ratio. To minimize electrical noises from the electrical circuits, silicon nitride was deposited as an insulation layer using a chemical vapor deposition process. Finally, electrode tips were covered with an Au layer for reduced contact resistance with cell membrane. The fabricated electrode was inserted into Chlamy cell using a glass micropipette connected to a micromanipulator. After nanoelectrode insertion into cells, light-sensitive currents were measured from the inserted cells using chronoamperometry. At the electrode potential of 400 mV versus an Ag/AgCl electrode, about 1.1 pA of currents were detected. Then, photosynthetic inhibitor tests were performed using a 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) solution. Addition of the DCMU solution to the Chlamy cells suppressed the generation of the photosynthetic currents, which indicated that the collected electrons originated from photosynthetic processes. To identify the sources of the photosynthetic electrons, the electrode potential bias was varied from 0 to 1.0 V versus the Ag/AgCl electrode. When higher potentials were applied, the amount of photo-responsive currents gradually increased in general. However, in the range between 200 to 400 mV, currents showed “rapid increase”. When the Z-scheme of photosynthesis is analyzed, at the electrode potential above 200 mV, only plastocyanine (PC), a mobile electron carrier can be oxidized. This indicates that PC is likely to be the major electron donor in our energy harvesting experiment.

A very promising synthesis pathway is presented for the encapsulation of the photosynthetically active entities such as chlorophyta Dunaliella tertiolecta in a core-shell system based upon a robust Alginate/silica hybrid matrix. Oximetry and fluorescence measurements highlight how this algal culture can remain photosynthetically active over a period of 9 months. The photosynthetic activity of our systems shows that the material was able to produce oxygen for over months to reduce CO₂ into carbohydrates. Instead of beads, this synthesis strategy has been applied to prepare Alginate/silica hybrid films to construct the photosynthetic solar cells. The photosynthetic material holds much promise in the development of new, green chemical processes. These results constitute a significant advance towards the final goal, long-lasting semi-artificial photosynthetic solar cells that can advantageously exploit solar radiation to convert polluting carbon dioxide into useful biofuels, sugars or medical metabolites and electricity.

The presentation will focus on describing recent results on assembling hybrid nanostructures composed of natural photosynthetic complexes and metallic nanostructures with an aim of developing ways of enhancing absorption of photosynthetic complexes by using plasmon excitations.The influence of plasmon excitations upon the optical properties of Photosystem I, Reaction Center from the Green Sulphur Bacteria, and the FMO complex, was investigated using variety of fluorescence microscopy and spectroscopy techniques. We find that in contrast to simple light-harvesting complexes, such as peridinin-chlorophyll-protein, these multichromophoric systems feature huge fluorescence enhancement factors, reaching up to 200. The enhancement strongly depend on the excitation wavelength, although we find no clear correlation between values of enhancement factors and extinction of metallic nanostructure. This indicates that by applying metallic nanostructures with defined geometry we can artificially enhance absorption in a certain spectral region, as well as even reverse the actual absorption efficiency of photosynthetic complexes.
Research supported by the WELCOME/2008/2 project funded by the Foundation for Polish Science, DEC-2013/11/B/ST3/03984 project from the National Science Center of Poland, and EUROCORES project “BOLDCATS” funded by the European Science Foundation.
N. Czechowski, H. Lokstein, D. Kowalska, K. Ashraf, R.J. Cogdell, S. Mackowski, "Large Plasmonic Fluorescence Enhancement of Cyanobacterial Photosystem I Coupled to Silver Island Films", Applied Physics Letters, 105, 043701/1-5 (2014)
M. Olejnik, B. Krajnik, D. Kowalska, M. Twardowska, N. Czechowski, E. Hofmann, S. Mackowski, "Imaging of fluorescence enhancement in photosynthetic complexes coupled to silver nanowires", Applied Physics Letters 102, 083703/1-5 (2013)
#321;. Bujak, N. Czechowski, D. Piatkowski, R. Litvin, S. Mackowski, T.H.P. Brotosudarmo, R.J. Cogdell
S. Pichler, W. Heiss, "Absorption Enhancement of LH2 Light-Harvesting Complexes Coupled to Spherical Gold Nanoparticles", Applied Physics Letters, 99, 173701/1-3 (2011)
S. Mackowski, S. Wörmke, A.J. Maier, T.H.P. Brotosudarmo, H. Harutyunyan, A. Hartschuh, A.O. Govorov, H. Scheer, C. Bräuchle, "Metal - Enhanced Fluorescence of Chlorophylls in Single Light - Harvesting Complexes", Nano Letters 8, 558-564 (2008)

Current state of the art transparent electrodes used in solar cells are indium tin oxide (ITO) for organic solar cells and fluorine-doped tin oxide (FTO) for dye-sensitized solar cells (DSSCs). ITO and FTO are relatively brittle, expensive, and suffer from chemical incompatibilities. Contrary to this, conductive boron-doped diamond is known to be one of the most stable and hardest materials. Although it is resistant to any chemical or biological environment, the stable sp3-bonded carbon surface allows the application of a rich surface chemistry enabling a strong and stable covalent bonding of organic molecules [1]. Thin (~150 nm) heavily boron-doped nanocrystalline diamond (B:NCD) films on glass provide thus an excellent electrode platform for (electrochemical) functionalization of the diamond surface with dye molecules. The p-type conductivity, which can be varied from 1 x 10^-9 to 100 Omega;^-1 cm^-1, turns such films into novel hole conducting electrodes for dye-sensitized solar cell applications.
As an illustrative system, the covalent attachment of N3 dye molecules [cis-bis(isothiocyanato)-bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium(II)] onto boron-doped nanocrystalline diamond (B:NCD) thin films will be discussed [2]. This goal is reached through a combination of coupling chemistries, i.e. diazonium, Suzuki and EDC-NHS. Diamond possesses the unique property that the absolute positions of valence and conduction band edges with respect to the vacuum level can be tuned, depending on the surface termination. For an efficient charge transfer, the energy levels of the dye and the diamond film need show a certain alignment. X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and near edge X-ray absorption fine structure spectroscopy (NEXAFS) are used to probe this alignment, while verifying the covalent bonding of the dye on the B:NCD surface. The spectroscopic results confirm the presence of a dense N3 chromophore layer. The positions of the frontier orbitals of the dye relative to the band edge of the B:NCD thin film show a promising configuration for charge transfer from the dye to the electrode, which is confirmed by photo-electrochemical measurements, displaying a strong increase in the detected photocurrent compared to bare diamond electrodes. These results present a first step towards the development of fully carbon-based devices for light to electricity conversion.
Financial support by the EU 7th Framework Programme, the Research Foundation Flanders (FWO), and Hasselt University is greatly acknowledged.
References:
[1] R.J. Nemanich, J.A. Carlisle, A. Hirata, K. Haenen, MRS Bulletin 39/6 (2014), 490-494.
[2] W.S. Yeap, X.J. Liu, D. Bevk, A. Pasquarelli, L. Lutsen, M. Fahlman, W. Maes, K. Haenen, ACS Applied Materials & Interfaces 6/13 (2014), 10322-10329.

Measuring photocurrents generated by monolayers of photosynthetic complexes adsorbed on conductive substrates offers a powerful tool to study the fundamental workings of photosynthesis based bioelectronics, biosensors and bio-photovoltaic devices.
Photosynthetic reaction centers consist of a precisely arranged series of cofactors that yield 100% QE charge separation. While elegant and optimized for its in vivo environment, interfacing these proteins with conducting substrates proves cumbersome, as the protein scaffold generally imposes a large barrier hindering efficient electron tunneling.
Here we report on the most important features of the various components active in our biophotovoltaic half cell for optimizing the interaction between the RC and the electrode surface: direct protein metal interactions, hard wired cytochrome c and a nanostructured substrate. In effect, optimal photocurrents are achieved in the presence of only Quinones in solution, in contrast with our previous conditions where both cytochrome c and quinones are present in solution (Hollander, 2011).
Furthermore, we show that the high quantum efficiency of the photosynthetic complexes are also retained in our biophotovoltaic half cells via enhanced electron transfer efficiency between the electrode and protein complex.

Nature has evolved the highly sophisticated architectures of photosynthetic complexes in plants and bacteria over several billion years to efficiently harvest sunlight for their survival. Natural photosystems have been of great interest, because their light-harvesting antenna complexes absorb sunlight and transport excitation energy with nearly 100% efficiency to a reaction center where converts the energy into chemical fuels. The design principles of such high transport efficiency can provide insight into conceiving efficient solar energy technologies. Until now, there has been intense focus of both experimental and theoretical efforts to elucidate the underlying mechanism of the energy transport in the light-harvesting complexes. Research in photosynthesis has suggested that nature uses the design principles such as the structural arrangement of chromophores, inter-chromophoric couplings, and exciton delocalization. However, the role of quantum coherence remains elusive in the natural light-harvesting complexes because of the innate limitations to their tunability. Here, using nature&’s design principles, I create a genetically tunable, artificial light-harvesting system for controlling chromophore networks of M13 bacteriophage. In this controllable system, the combination of spectroscopic analysis and dynamic modeling illuminates an intermediate regime showing the interplay of quantum coherent and classical, incoherent exciton transport at room temperature. Furthermore, this interplaying regime achieves a significant enhancement of the energy transport, which suggests that quantum transport can play a key role in maximizing efficiency in solar energy applications such as organic photovoltaic devices and photocatalytic water splitting cells.

The artificial leaf project calls for new materials enabling multielectron catalysis with minimal
overpotential, high turnover frequency, and long-term stability.
Here we show the new discovery of a mixed-valence tetramanganese core shaped by a hybrid organic-inorganic coordination sphere that mimicks the Oxygen Evolving Center of the natural PSII enzyme. Our results include the design of functionalized graphene providing an sp² carbon nano-platform to anchor the artificial analog of the PSII reactive core. The resulting hybrid material displays oxygen evolution at overpotential as low as 300 mV at neutral pH. This multi-layer electroactive asset enhances the turnover frequency by one order of magnitude with respect to the isolated catalyst.
References
1. F. Paolucci, M. Prato, and M. Bonchio et al., ACS nano, 7, 811, 2013
2. Bonchio, M.; Fabris, S. et al. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, 4917-4922.
3. S.; Scandola, F.; Kortz, U.; Bonchio, M. Angew. Chem. Int. Ed., 2014.

The Rhodobacter sphaeroides photosynthetic reaction center is a robust and malleable integral membrane protein that lends itself to the construction of biohybrid devices for a range of applications in photovoltaics, biosensing, photocatalysis and molecular electronics. One key issue in the use of such proteins is controlling how they interact with conducting surfaces and other device components in order to optimise function, maximise stability and simplify fabrication procedures. To date these issues have largely been addressed through selection and surface modification of electrode materials, and the manipulation of mediators and reaction conditions. However, engineering of the proteins themselves to control adsorption and assembly at the electrode surface through genetic encoding remains largely unexplored. To this end we have modified the atomic structure of the reaction center protein in variety of ways to direct specific associations with conducting materials and to gain control over the way that individual proteins self-assemble into long-range oligomeric structures both in vivo and in vitro. We have also explored the use of lipid-polymer nanodiscs as an alternative vehicle for housing photovoltaic reaction centres, dispensing with the need to employ detergents during protein extraction from the membrane and subsequent purification. These nanodiscs preserve native functional properties that are modified on exposure to detergent, and provide a stabilising environment in which to house the reaction center protein. Recent progress in these areas will be described.

Artificial photosynthesis may represent an inexpensive means of converting the energy in sunlight into clean chemical fuels. Most artificial photosynthetic systems mimic nature&’s properties of light absorption, electronic charge separation, and electronic charge collection, so that electrons can ultimately make and break chemical bonds. However, nature also transduces photon energy into proton gradients whose electrical potential also drives chemical-bond formation. In my presentation I will report on my research group&’s progress toward mimicking nature in function, by using the energy in light to drive endergonic ion-transfer reactions for light-to-ionic energy conversion. The applicability and practicality of this material as a membrane in solar fuels devices and as a separate ionic photovoltaic device will also be discussed.
My research group&’s primary goal is to provide a proof-of-concept demonstration of an artificial proton pump that performs photovoltaic action through ion motion. For an initial model system we utilized a conical nanopore etched in a polyethylene terephthalate plastic sheet. This pore was formed via swift heavy ion bombardment followed by alkaline chemical etching. The pore was functionalized using peptide coupling chemistries to generate regions containing fixed cationic, anionic, and neutral functional groups. Novel photoacid molecules were also covalently anchored into the proposed electrostatic depletion region of the nanopores. It was hypothesized that under visible-light illumination and a small reverse bias, liberated protons would generate an ionic photocurrent and indeed one was observed. We are currently expanding this initial research and successful demonstration of an artificial light-driven ion pump to other polymeric materials.

Efficient biophotoelectrochemical and bio-photovoltaic cells require fast electron transfer at low overpotential. At the single protein level extremely fast direct electron transfer between photosynthetic proteins and electrodes can be achieved without loss of voltage [1]. However, the upscaling from the single protein to large ensembles doubly connected in the direct electron transfer mode is challenging.
Instead, electron relays provide an efficient alternative toward high power density at the condition that their propershy;ties, and in particular their redox potentials, are tuned to enable maximal current density at low overpotential. To illustrate the desired parameters of an electron relay and of its polymeric supporting matrix, the example of bio-photoelectrochemical cell as well as a full bio-photovoltaic cells based on photosynthetic protein complexes will be given [2,3]. In particular, the performances of a PS1 photocathode are sufficiently high to envision technological applications in biophotovoltaic devices [4].
Besides the solar energy to electricity conversion, the production of chemical fuels from catalyst coupled to the biophotochemical processes will be discussed. In particular the implementation of hydrogenase in redox hydrogels allows for protection of this sensitive biocatalyst from high potential deactivation and oxygen damage which are typically encountered in technological applications [5]. Various further strategies for shielding from oxygen damage that may also occur in biophotovoltaic devices will be presented [6,7].
Literature
[1] a) N. Plumeré, Nature Nanotech., 2012, 7(10), 616-617; b) D. Gerster, J. Reichert, H. Bi, J. V. Barth, S. M. Kaniber, A. W. Holleitner, I. Visoly-Fisher, S. Sergani and I. Carmeli, Nature Nanotech., 2012, 7, 673-676.
[2] T. Kothe, N. Plumeré, A. Badura, M. M. Nowaczyk, D. A. Gushin, M. Rögner, W. Schuhmann, Angew. Chem. Int. Ed., 2013, 52, 14233 -14236.
[4] T. Kothe, S. Pöller, F. Zhao, P. Fortgang, M. Rögner, W. Schuhmann, N. Plumeré Chemistry - A European Journal,2014, 20, 11029 - 11034.
[5] N. Plumeré, O. Rüdiger, A. Alsheikh Oughli, R. Williams, J. Vivekananthan, S. Pöller, W. Schuhmann, W. Lubitz, Nature Chemistry, 2014, 6, 822-827.
[6] N. Plumeré, J. Henig and W. H. Campbell, Anal. Chem. 2012, 84, 2141-2146.
[7] M. Swoboda, J. Henig, H.-M. Cheng, D. Brugger, D. Haltrich, N. Plumeré, M. Schlierf, ACS Nano, 2012, 6(7), 6364-6369.
Financial support by the Cluster of Excellence RESOLV (EXC 1069) funded by the Deutsche Forschungsgemeinschaft is gratefully acknowledged.

The first bio-hybrid electrodes were used by Melvin Calvin in the late 1950s where he sublimated chlorophyll on aquadag graphite interdigital electrodes. This was done merely to study the bio-organic material. Helmut Tributsch' dye-sensitized solar cells (DSSC) in the early 1970s were ZnO electrodes, i.e. semiconductors further functionalized with natural absorbing dye molecules. Since, DSSCs have developed as a field in photovoltaic solar energy conversion technology. Meanwhile, photoelectrodes for solar water splitting in photoelectrochemical cells (PEC) evolved as an independent field. This field has recently emerged again and is virtually taking center stage. Also here, functionalization of traditional semicondcutor electrodes with bio-organic motifs is gaining more and more interest. Hydrogenase is a frequently used protein for the promotion of hydrogen evolution on photocathodes. We have recently coated the light harvesting antenna protein C-phycocyanin on iron oxide photoelectrodes. This approach was quite promising. We measured an increrased photocurrent density at the photoanode and an increased hydrogen evolution at the counter electrode. During our studies we were pointed to the question of charge transfer across the bio-electronic interface which is formed by biomolecules and metal oxides. Because the expressioan and purification of C-phycocyanin, which is extracted from cyanobacteria, is a costly and laborious process, we explored also the use of complete cyanobacteria on the photoelectrodes. The thylakoid membrane and cell membrane may pose electrical barriers between the biocatalytic or light harvesting components in the photosynthetic apparatus and the semicondcutor electrode underneath. It is therefore necessary to quantify this barrier. For this, we are performing electroanalytical experiments and x-ray spectroscopy experiments operando and in situ.
[1] J. Ihssen, A. Braun, G. Faccio, K. Gajda-Schrantz, L. Thöny-Meyer; Light harvesting proteins for solar fuel generation in bioengineered photoelectrochemical cells; Current Protein and Peptide Science, 2014, 15 (4),374-384.
[2] D. K. Bora, Y. Hu, S. Thiess, S. Erat, X. Feng, S. Mukherjee, G. Fortunato, N. Gaillard, R. Toth, K. Gajda-Schrantz, W. Drube, M. Grätzel, J. Guo, J. Zhu, E.C. Constable, D.D. Sarma, H. Wang, A. Braun, Between Photocatalysis and Photosynthesis: Synchrotron spectroscopy methods on molecules and materials for solar hydrogen generation, J. Electron Spectr. Rel. Phenom. 2013, 190 A, 93-105.
[3] D.K. Bora, A.A. Rozhkova, K. Schrantz, P.P. Wyss, A. Braun, T. Graule, E.C. Constable, Functionalization of Nanostructured Hematite Thin-Film Electrodes with the Light-Harvesting Membrane Protein C-Phycocyanin Yields an Enhanced Photocurrent, Advanced Functional Materials 2012, 22 (3) 490-502.
[4] D.K. Bora, A. Braun, E.C. Constable, “In rust we trust”. Hematite the prospective inorganic backbone for artificial photosynthesis, Energy Environ. Sci., 2013,6, 407-425.

Pt is a still dominant counter electrode material in a dye-sensitized solar cell (DSC) although lots of promising materials such as carbon, graphene, and polymer have challenged to replace conventional Pt counter electrode so far. It is not easy to find a special material with high catalytic activity, good charge transfer, and sufficient contact. Polymeric materials are also one of good candidates. Especially, its low cost is incomparable with other promising materials for realizing cheap and highly efficient photovoltaic devices. Good conductive polymer, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS), was already applied to counter electrode of DSC but its low catalytic activity deteriorated photovoltaic performance with low fill factor. Slow catalytic reaction caused electron jam at the counter electrode and slow dye regeneration. In this work, performance of DSC with PEDOT:PSS counter electrode was also low due to insufficient catalytic activity of polymeric counter electrode. In order to improve catalytic reaction of PEDOT:PSS counter electrode, TiO₂ nano-particles were introduced to PEDOT:PSS counter electrode. The mixture of PEDOT:PSS and TiO₂ was deposited on counter electrode. Surface area of PEDOT:PSS counter electrode was increased by nano-particles and the catalytic reaction was activated. Their catalytic and photovoltaic properties were analyzed according to the amount of TiO₂ nano-particles. As a result, the catalytic reaction of PEDOT:PSS counter electrode was much activated with TiO₂ amount. Catalytic activation supplied more electrons into electrolyte and dye regeneration was quickened. The photovoltaic performance of activated polymeric counter electrode was consequently higher than that of Pt counter electrode. Final performance of a DSC with improved PEDOT:PSS counter electrode was defined by 0.72 V of V_OC, 14.06 mA/cm² of J_SC, 0.72 of FF, and 7.24% of efficiency while the performance of a DSC with Pt counter electrode had 0.72 V of V_OC, 12.65 mA/cm² of J_SC, 0.71 of FF, and 6.50% of efficiency.

Two important reasons make the design and construction of small protein functional analogs of photosynthetic proteins an appealing strategy toward novel sloar energy conversion devices. First, it provides simple models to the elaborate multi-protein multi-cofactor complexes that carry out natural photosynthesis, and thereby a way to study the fundamental engineering principles of biological solar energy conversion and learn how to implement these principles outside their biological context. Second, successful designs may be integrated with artificial and/or natural components into novel systems for the production of viable solar fuels. Our focus is on natural photosynthetic light-harvesting complexes in which dense arrays of chlorophylls, phycobilins, and/or carotene derivatives are held in place by specific binding proteins. The particular arrangement of chromophores and their specific protein environment allows precise control of the non-radiative energy dissipation processes that prevail in such dense arrays of pigments. This enables regulating the photon fluxes throughout the light harvesting system and directing excitation energy toward its final destination the reaction center. The mechanisms underlying energy transfer and dissipation within the complicated network of chromophores in natural light-harvesting complexes are not completely clear. By designing small water-soluble proteins that are capable of binding and assembling a few chlorophyll and/or phycobilin derivatives we are able to rigorously characterizatize energy transfer and dissipation mechanisms by systematic manipulation of pigment types, relative orientations, and local protein environments. Recent examples include 1) the conversion of a native transmembranal chlorophyll binding motif into a water-soluble protein capable of binding up to seven bacteriochlorophyll derivatives, 2) fusion proteins combining a natural phycobilin-binding protein domain and a de novo designed porphyrin- or chlorophyll-binding protein domain, and 3) a new reconstitution protocol for water-soluble chlorophyll binding proteins with native hydrophobic chlorophyll derivatives. From these we learn important lessons on controlling photexctation dynamics in multipigment protein complexes. For example, our Stark spectroscopy study of zinc-substituted bacteriochlorophyllide dimers bound to HP7, a de novo designed four-helix bundle protein emphasize the importance of controlling the energetics of charge-transfer states in excitonically coupled chlorophyll pairs. It suggests a general mechanism for determining the fate of the pair&’s photoexcited state and switching between energy-transfer, energy-dissipation and charge-separation.

Protein film photoelectrochemistry (PF-PEC) allows for the light-dependent activity of Photosystem II (PSII) adsorbed onto an electrode surface to be studied.¹ We have recently made progress in the direct integration of PSII in conducting metal oxide electrodes. PSII from Thermosynechococcus elongatus was adsorbed on a nanostructured and transparent indium-tin oxide (ITO) electrode for visible light driven water oxidation to O₂ and non-mediated electron transfer was observed at the enzyme-electrode interface.² A rational strategy to electrostatically orient and covalently immobilise PSII on the ITO electrode was also developed, resulting in enhanced photocurrent response and film stability.³ In these studies, PF-PEC was shown to provide us with valuable insights into the activity, stability, quantum yields, and interfacial electron transfer pathways of PSII.

Tunable protein scaffolds labeled with light-absorbing molecules are a promising platform for biomimetic light harvesting systems. While the spectrum-enhancing capabilities and ultrafast excitation transfer properties of chromophore arrays within these biomimetic constructs have been discussed, the change in the properties of individual chromophore units as they are inserted into this artificial environment has not been quantified.
Using time-resolved absorption and fluorescence measurements, we report the effects of rigidification and confinement on fluorescent molecules covalently attached to the interior of the nanometer-sized cavity of a circular permutant of the tobacco mosaic virus capsid double-disk assembly. The ultrafast population dynamics of such fluorophores become significantly slower within the cavity when compared to bulk solvent, and slower as the fluorophores are inserted deeper into the cavity. We observe three distinct signatures of this spatially-dependent molecular environment: (1) hydration dynamics substantially slower than bulk solvent, (2) hindered molecular rearrangements, and (3) enhancement of the excitation lifetime of a flexible fluorophore.
These effects can be explained by considering that the molecular environment of the fluorophore, solvent, and protein becomes progressively rigidified as a function of position within the cavity. It is important to note that the fluorophore size is comparable to the cavity dimensions, and excludes a non-negligible amount of solvent from this cavity. The interactions between fluorophore, solvent molecules, and protein within a confined geometry result in a system where each component plays an important role in determining the excited state population dynamics.
An important observation from this work is that while dyes with rigid structures are favored due to their longer excitation lifetimes, this rigidity can be built into the protein-solvent-chromophore environment and does not necessarily have to be built into the chemical identity of the chromophore. Differences in solvation and confinement such as those observed in this work are thus a powerful determinant of the properties of small molecules within protein cavities, and should be incorporated into the design of biohybrid systems.

Solar energy is an environmentally friendly alternative energy source that can make a significant contribution to solving worldwide energy problems. Low-cost and easy fabrication of dye-sensitized solar cells make this type of devices very promising for future indoor and outdoor applications. Though greater than 13% energy conversion efficiency has been achieved in a zinc porphyrin-sensitized solar cell, low energy conversion efficiency and poor long-term stability are still two major concerns in regard to its competitiveness with other types of solar cells. In this talk, several strategies will be presented to address these barriers. We found that inserting a thiophene or a fluorene unit between a donor and an acceptor in porphyrin structures led to the gradual broadening of the absorption spectra, resulting in increased energy conversion efficiency. However, adding a small complementary BODIPY dye in a porphyrin solution during the dye-loading process may or may not benefit the energy conversion depending upon the porphyrin structures. Further studies also showed that replacement of a benzoic acid by an 8-hydroxyquinoline significantly increased the binding strength of the dye molecules on titanium dioxide nanoparticles. The trade-off of these strategies will also be discussed.