Natural photosynthesis can be divided between the chlorophyll-containing plants, algae and cyanobacteria that make up the oxygenic phototrophs and a diversity of bacteriochlorophyll-containing ...bacteria that make up the anoxygenic phototrophs. Photosynthetic light harvesting and reaction centre proteins from both kingdoms have been exploited for solar energy conversion, solar fuel synthesis and sensing technologies, but the energy harvesting abilities of these devices are limited by each protein's individual palette of pigments. In this work we demonstrate a range of genetically-encoded, self-assembling photosystems in which recombinant plant light harvesting complexes are covalently locked with reaction centres from a purple photosynthetic bacterium, producing macromolecular chimeras that display mechanisms of polychromatic solar energy harvesting and conversion. Our findings illustrate the power of a synthetic biology approach in which bottom-up construction of photosystems using naturally diverse but mechanistically complementary components can be achieved in a predictable fashion through the encoding of adaptable, plug-and-play covalent interfaces.
In a quest to fabricate novel solar energy materials, the high quantum efficiency and long charge separated states of photosynthetic pigment‐proteins are being exploited through their direct ...incorporation in bioelectronic devices. In this work, a biohybrid photocathode comprised of bacterial reaction center‐light harvesting 1 (RC‐LH1) complexes self‐assembled on a nanostructured silver substrate yields a peak photocurrent of 166 μA cm−2 under 1 sun illumination, and a maximum of 416 μA cm−2 under 4 suns, the highest reported to date on a bare metal electrode. A 2.5‐fold plasmonic enhancement of light absorption per RC‐LH1 complex is observed on the rough silver substrate. This plasmonic interaction is assessed using confocal fluorescence microscopy, revealing an increase of fluorescence yield, and radiative rate of the RC‐LH1 complexes, signatures of plasmon‐enhanced fluorescence. Nanostructuring of the silver substrate also enhanced the stability of the protein under continuous illumination by almost an order of magnitude relative to a nonstructured bulk silver control. Due to its ease of construction, increased protein loading capacity, stability, and more efficient use of light, this hybrid material is an excellent candidate for further development of plasmon‐enhanced biosensors and biophotovoltaic devices.
A novel biohybrid photocathode consisting of photosynthetic complexes is revealed on a nanostructured silver electrode. This photocathode nets record photocurrents up to 416 μA cm−2 in part thanks to a 2.5‐fold plasmon‐enhanced light harvesting efficiency.
The exploitation of natural photosynthetic enzymes in semi‐artificial devices constitutes an attractive and potentially sustainable route for the conversion of solar energy into electricity and solar ...fuels. However, the stability of photosynthetic proteins after incorporation in a biohybrid architecture typically limits the operational lifetime of biophotoelectrodes to a few hours. Here, we demonstrate ways to greatly enhance the stability of a mesoporous electrode coated with the RC‐LH1 photoprotein from Rhodobacter sphaeroides. By preserving electron transfer pathways, we extended operation under continuous high‐light to 33 days, and operation after storage to over two years. Coupled with large photocurrents that reached peak values of 4.6 mA cm−2, the optimized biophotoelectrode produced a cumulative output of 86 C cm−2, the largest reported performance to date. Our results demonstrate that the factor limiting stability is the architecture surrounding the photoprotein, and that biohybrid sensors and photovoltaic devices with operational lifetimes of years are feasible.
The viability of biohybrid technologies is primarily limited by the inherent fragility of the biological component. The operational stability of photoproteins adsorbed to mesoporous ITO electrodes is prolonged to 33 days under intense illumination, and 28 months in storage, demonstrating the feasibility of protein‐based devices that last years.
The high quantum efficiency of photosynthetic reaction centers (RCs) makes them attractive for bioelectronic and biophotovoltaic applications. However, much of the native RC efficiency is lost in ...communication between surface-bound RCs and electrode materials. The state-of-the-art biophotoelectrodes utilizing cytochrome c (cyt c) as a biological wiring agent have at best approached 32% retained RC quantum efficiency. However, bottlenecks in cyt c-mediated electron transfer have not yet been fully elucidated. In this work, protein film voltammetry in conjunction with photoelectrochemistry is used to show that cyt c acts as an electron-funneling antennae that shuttle electrons from a functionalized rough silver electrode to surface-immobilized RCs. The arrangement of the two proteins on the electrode surface is characterized, revealing that RCs attached directly to the electrode via hydrophobic interactions and that a film of six cyt c per RC electrostatically bound to the electrode. We show that the additional electrical connectivity within a film of cyt c improves the high turnover demands of surface-bound RCs. This results in larger photocurrent onset potentials, positively shifted half-wave reduction potentials, and higher photocurrent densities reaching 100 μA cm
. These findings are fundamental for the optimization of bioelectronics that utilize the ubiquitous cyt c redox proteins as biological wires to exploit electrode-bound enzymes.
•Description of the potential power conversion efficiency of photosynthetic reaction centers.•Summary of key developments, progress, and current benchmarks in biophotoelectrodes.•Insights for ...electrode construction for obtaining practical efficiencies.
Photosynthesis is the principal solar energy conversion process on Earth, but is low in overall efficiency due to numerous steps necessary to fix carbon. Tapping into the high-efficiency components which drive photosynthesis, known as reaction centers, offers a route to efficiently capture solar energy. This may be achieved by direct integration of reaction centers onto electrode materials in order to extract the high potential electrons and produce electricity or fuels. This review describes the various strategies and current benchmark configurations of Photosystem-I, Photosystem-II and bacterial reaction center-based biophotoelectrodes.
The Rhodobacter sphaeroides reaction centre is a relatively robust and tractable membrane protein that has potential for exploitation in technological applications, including biohybrid devices for ...photovoltaics and biosensing. This report assessed the usefulness of the photocurrent generated by this reaction centre adhered to a small working electrode as the basis for a biosensor for classes of herbicides used extensively for the control of weeds in major agricultural crops. Photocurrent generation was inhibited in a concentration-dependent manner by the triazides atrazine and terbutryn, but not by nitrile or phenylurea herbicides. Measurements of the effects of these herbicides on the kinetics of charge recombination in photo-oxidised reaction centres in solution showed the same selectivity of response. Titrations of reaction centre photocurrents yielded half maximal inhibitory concentrations of 208nM and 2.1µM for terbutryn and atrazine, respectively, with limits of detection estimated at around 8nM and 50nM, respectively. Photocurrent attenuation provided a direct measure of herbicide concentration, with no need for model-dependent kinetic analysis of the signal used for detection or the use of prohibitively complex instrumentation, and prospects for the use of protein engineering to develop the sensitivity and selectivity of herbicide binding by the Rba. sphaeroides reaction centre are discussed.
•The Rhodobacter sphaeroides reaction centre was used as a biosensor for herbicides.•Herbicide concentration was assessed through the attenuation of a photocurrent.•The biosensor showed selectivity for triazine herbicides.•The limit of detection of the biosensor was in the low nanomolar range.•Photocurrent attenuation is a simple and direct basis for a herbicide biosensor.
While the role of collagen and elastin fibrous components in heart valve valvular biomechanics has been extensively investigated, the biomechanical role of the glycosaminoglycan (GAG) gelatinous-like ...material phase remains unclear. In the present study, we investigated the biomechanical role of GAGs in porcine aortic valve (AV) leaflets under tension utilizing enzymatic removal. Tissue specimens were removed from the belly region of porcine AVs and subsequently treated with either an enzyme solution for GAG removal or a control (buffer with no enzyme) solution. A dual stress level test methodology was used to determine the effects at low and high (physiological) stress levels. In addition, planar biaxial tests were conducted both on-axis (i.e. aligned to the circumferential and radial axes) and at 45° off-axis to induce maximum shear, to explore the effects of augmented fiber rotations on the fiber–fiber interactions. Changes in hysteresis were used as the primary metric of GAG functional assessment. A simulation of the low-force experimental setup was also conducted to clarify the internal stress system and provide viscoelastic model parameters for this loading range. Results indicated that under planar tension the removal of GAGs had no measureable affect extensional mechanical properties (either on- or 45° off-axis), including peak stretch, hysteresis and creep. Interestingly, in the low-force range, hysteresis was markedly reduced, from 35.96±2.65% in control group to 25.00±1.64% (p<0.001) as a result of GAG removal. Collectively, these results suggest that GAGs do not play a direct role in modulating the time-dependent tensile properties of valvular tissues. Rather, they appear to be strongly connected with fiber–fiber and fiber–matrix interactions at low force levels. Thus, we speculate that GAGs may be important in providing a damping mechanism to reduce leaflet flutter when the leaflet is not under high tensile stress.
Reaction centre/light harvesting proteins such as the RCLH1X complex from Rhodobacter sphaeroides carry out highly quantum-efficient conversion of solar energy through ultrafast energy transfer and ...charge separation, and these pigment-proteins have been incorporated into biohybrid photoelectrochemical cells for a variety of applications. In this work we demonstrate that, despite not being able to support normal photosynthetic growth of Rhodobacter sphaeroides, an engineered variant of this RCLH1X complex lacking the PufX protein and with an enlarged light harvesting antenna is unimpaired in its capacity for photocurrent generation in two types of bio-photoelectrochemical cells. Removal of PufX also did not impair the ability of the RCLH1 complex to act as an acceptor of energy from synthetic light harvesting quantum dots. Unexpectedly, the removal of PufX led to a marked improvement in the overall stability of the RCLH1 complex under heat stress. We conclude that PufX-deficient RCLH1 complexes are fully functional in solar energy conversion in a device setting and that their enhanced structural stability could make them a preferred choice over their native PufX-containing counterpart. Our findings on the competence of RCLH1 complexes for light energy conversion in vitro are discussed with reference to the reason why these PufX-deficient proteins are not capable of light energy conversion in vivo.
Photosynthetic reaction centers catalyze the majority of solar energy conversion on the Earth. Under low-intensity illumination, this is achieved with a near-unity quantum efficiency, almost every ...absorbed photon producing a photochemical charge separation. Biohybrid technologies seek to capture the high efficiency of natural photoproteins by combining them with man-made electrodes. However, the transfer of photoproteins from their membrane environment into an abiotic architecture invariably results in efficiency losses. Here, we combined spectroscopy and analytical electrochemistry to identify the loss processes in a reaction-center-based biophotoelectrode. While over 90% efficient under low-intensity illumination, the biophotoelectrode efficiency dropped to ∼11% under high-intensity illumination. This loss stemmed from bottlenecks in electron transfer that rendered 60% of reaction centers inactive, as well as a short-circuiting of 73% of the separated charge from active reaction centers. The quantitative insights into loss processes presented in this work will be instrumental in shaping future rational design of biophotoelectrode devices.
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•A protein-photoelectrode was investigated with spectroscopy and electrochemistry•We resolved electron flow and energy loss channels during biohybrid operation•Continuous intense irradiation exacerbated loss channels and compromised efficiency•The knowledge will help drive the rational design of more efficient biohybrids
Solar energy fuels life in two ways: through photosynthesis, providing food for virtually all organisms on the Earth; and by generating electricity in photovoltaic devices. Biohybrid photoelectrodes combine the best of both worlds, coupling natural-light-driven photoenzymes with complex artificial materials in a bid to achieve sustainable, low-power tools. These may be used in a wide range of applications, from the production of solar fuels and value-added chemicals to electricity. However, bridging nature and technology often proves challenging, as biohybrid devices remain inefficient and unstable due to the creation of harmful side reactions. Using combined spectroscopic and electrochemical tools, we discover the origin of productivity losses during the operation of a state-of-the-art biohybrid device. A comprehensive quantification of loss processes is provided together with a blueprint for removal of these hurdles, bringing us closer to a zero-carbon economy driven by sustainable photoenzymes.
In this work, we combined electrochemistry and spectroscopy to analyze electron flow through a protein-based photoelectrode. Such biophotoelectrodes form a platform for biosolar cells, where the processes of solar energy capture and conversion take place within natural photosynthetic proteins. We show that both non-native electron transfer to/from the photoenzyme and a variety of short-circuit loops limit biohybrid performance under operating conditions. The findings are crucial for the development of strategies to block loss channels and enable efficient protein-based biotechnologies.
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