Photosynthetic apparatus of Rhodobacter sphaeroides exhibits prolonged charge storage

Unraveling the Photovoltage Formation Mechanism in Indium-Tin Oxide Branched Nanowires/Poly(3-Hexylthiophene) Photorechargeable Supercapacitors

Photorechargeable supercapacitors are promising next-generation renewable energy storage devices. Previously, a hybrid structure consisting of indium-tin oxide branched nanowires (ITO BRs) and poly(3-hexylthiophene) (P3HT) was demonstrated as a photorechargeable supercapacitor. However, the formation mechanism of photovoltage has not been studied. Herein, we experimentally investigated the photovoltage-determining parameters in the ITO BRs/P3HT photorechargeable supercapacitor by inserting a polyethylenimine ethoxylated (PEIE) interlayer or adding a phenyl-C61-butyric acid methyl ester (PCBM) electron acceptor. Coating the PEIE interlayer on ITO BRs decreased the work function by 0.5 eV and hindered the hole extraction from P3HT to ITO BRs, leading to interfacial recombination and a decrease in photovoltage. On the other hand, the addition of PCBM promoted the charge transfer of the electrons from P3HT to PCBM, enhanced the redox reaction at the PCBM/electrolyte interface, and reduced the number of accumulated electrons, leading to a decreased photovoltage. From these results, we found that two key parameters determine the photovoltage and charge storage capability; one is the interfacial recombination at the ITO BRs/P3HT interface and the other is the redox reaction at the P3HT/electrolyte interface.

Pulsed Force Kelvin Probe Force Microscopy-A New Type of Kelvin Probe Force Microscopy under Ambient Conditions

Kelvin probe force microscopy (KPFM) is an increasingly popular scanning probe microscopy technique used for nanoscale imaging of surface potential for various materials, such as metals, semiconductors, biological samples, and photovoltaics, to reveal their surface work function and/or local accumulation of charges. This featured review outlines the operation principles and applications of KPFM, including several typical commercially available variants. We highlight the significance of surface potential measurements, present the details of the method operation, and discuss the causes of the limitation on spatial resolution. Then, we present the pulsed force Kelvin probe force microscopy (PF-KPFM) as an innovative improvement to KPFM, which provides an enhanced spatial resolution of <10 nm under ambient conditions. PF-KPFM is promising for the characterization of heterogeneous materials with spatial variations of electrical properties. It will be especially instrumental for investigating emerging perovskite photovoltaics, heterogeneous catalysts, 2D materials, and ferroelectric materials, among others.

Light energy utilization and microbial catalysis for enhanced biohydrogen: Ternary coupling system of triethanolamine-mediated Fe@C-Rhodobacter sphaeroides

This study investigated the mediating effect of Triethanolamine on Fe@C-Rhodobacter sphaeroides hybrid photosynthetic system to achieve efficient biohydrogen production. The biocompatible Fe@C generates excited electrons upon exposure to light, releasing ferrum for nitrogenase synthesis, and regulating the pH of the fermentation environment. Triethanolamine was introduced to optimize the electron transfer chain, thereby improving system stability, prolonging electron lifespan, and facilitating ferrum corrosion. This, in turn, stimulated the lactic acid synthetic metabolic pathway of Rhodobacter sphaeroides, resulting in increased reducing power in the biohybrid system. The ternary coupling system was analyzed through the regulation of concentration, initial pH, and light intensity. The system achieved the highest total H2 production of 5410.9 mL/L, 1.29 times higher than the control (2360.5 mL/L). This research provides a valuable strategy for constructing ferrum-carbon-based composite-cellular biohybrid systems for photo-fermentation H2 production.

Constructing liquid metal/metal-organic framework nanohybrids with strong sonochemical energy storage performance for enhanced pollutants removal

With endogenous redox systems and multiple enzymes, the storage and utilization of external energy is general in living cells, especially through photo/ultrasonic synthesis/catalysis due to in-situ generation of abundant reactive oxygen species (ROS). However, in artificial systems, because of extreme cavitation surroundings, ultrashort lifetime and increased diffusion distance, sonochemical energy is rapidly dissipated via electron-hole pairs recombination and ROS termination. Here, we integrate zeolitic imidazolate framework-90 (ZIF-90) and liquid metal (LM) with opposite charges by convenient sonosynthesis, and the resultant nanohybrid (LMND@ZIF-90) can efficiently capture sonogenerated holes and electrons, and thus suppress electron-hole pairs recombination. Unexpectedly, LMND@ZIF-90 can store the ultrasonic energy for over ten days and exhibit acid-responsive release to trigger persistent generation of various ROS including superoxide (O₂•^-), hydroxyl radicals (•OH), and singlet oxygen (¹O₂), presenting significantly faster dye degradation rate (short to seconds) than previously reported sonocatalysts. Moreover, unique properties of gallium could additionally facilitate heavy metals removal through galvanic replacement and alloying. In summary, the LM/MOF nanohybrid constructed here demonstrates strong capacity for storing sonochemical energy as long-lived ROS, enabling enhanced water decontamination without energy input.

Scalable Manufacturing of Environmentally Stable All-Solid-State Plant Protein-Based Supercapacitors with Optimal Balance of Capacitive Performance and Mechanically Robust

The development of advanced biomaterial with mechanically robust and high energy density is critical for flexible electronics, such as batteries and supercapacitors. Plant proteins are ideal candidates for making flexible electronics due to their renewable and eco-friendly natures. However, due to the weak intermolecular interactions and abundant hydrophilic groups of protein chains, the mechanical properties of protein-based materials, especially in bulk materials, are largely constrained, which hinders their performance in practical applications. Here, a green and scalable method is shown for the fabrication of advanced film biomaterials with high mechanical strength (36.3 MPa), toughness (21.25 MJ m^-3 ), and extraordinary fatigue-resistance (213 000 times) by incorporating tailor-made core-double-shell structured nanoparticles. Subsequently, the film biomaterials combine to construct an ordered, dense bulk material by stacking-up and hot-pressing techniques. Surprisingly, the solid-state supercapacitor based on compacted bulk material shows an ultrahigh energy density of 25.8 Wh kg^-1 , which is much higher than those previously reported advanced materials. Notably, the bulk material also demonstrates long-term cycling stability, which can be maintained under ambient condition or immersed in H₂ SO₄ electrolyte for more than 120 days. Thus, this research improves the competitiveness of protein-based materials for real-world applications such as flexible electronics and solid-state supercapacitors.

DNA-nanostructure-templated assembly of planar and curved lipid-bilayer membranes

Lipid-bilayer nanodiscs and liposomes have been developed to stabilize membrane proteins in order to study their structures and functions. Nanodiscs are detergent-free, water-soluble, and size-controlled planar phospholipid-bilayer platforms. On the other hand, liposomes are curved phospholipid-bilayer spheres with an aqueous core used as drug delivery systems and model membrane platforms for studying cellular activities. A long-standing challenge is the generation of a homogenous and monodispersed lipid-bilayer system with a very wide range of dimensions and curvatures (elongation, bending, and twisting). A DNA-origami template provides a way to control the shapes, sizes, and arrangements of lipid bilayers via enforcing the assembly of lipid bilayers within the cavities created by DNA nanostructures. Here, we provide a concise overview and discuss how to design planar and curved lipid-bilayer membranes by using DNA-origami nanostructures as templates. Finally, we will discuss the potential applications of DNA-origami nanostructures in the structural and functional studies of large membrane proteins and their complexes.

Plasmonic protein electricity generator

Interest in acquiring green energy from sunlight is driving research into the incorporation of biological photosynthetic materials into biohybrid devices. A potential way to enhance solar energy conversion by photosynthetic proteins is to couple them to plasmonic nanomaterials to enhance absorption of incident radiation. In this work, a variety of plasmonic nanoparticles were used to boost the photocurrent output of a Protein Electricity Generator (PEG). Mixing gold nanoparticles (NPs) of five different architectures into the photoprotein/electrolyte contents of the cell was found to increase device performance, the most effective being ∼120 nm diameter star-shaped clusters that caused a ∼six-fold increase in photocurrent at the optimum dopant level. In addition, high-resolution electrohydrodynamic printing was used to create parallel line and square lattice patterns of silver nanoparticle ink on the tungsten rear electrode of the cells. Patterns with a 700 nm spacing between lines boosted photocurrents by up to three-fold and the effects of the gold and silver nanoparticles were additive, such that the ideal combination produced a ∼19-fold increase in photocurrent and device efficiency. We attribute the elevated performance to plasmonic enhancement of absorbance and scattering effects that increase the path length for photons in the device. Use of rear electrodes with silver nanoparticle lines and grids at 1100 nm spacing did not increase photocurrents, highlighting the importance of precision printing of nanostructures for the enhancement of device performance.

Bio-inspired strategies for next-generation perovskite solar mobile power sources

Smart electronic devices are becoming ubiquitous due to many appealing attributes including portability, long operational time, rechargeability and compatibility with the user-desired form factor. Integration of mobile power sources (MPS) based on photovoltaic technologies with smart electronics will continue to drive improved sustainability and independence. With high efficiency, low cost, flexibility and lightweight features, halide perovskite photovoltaics have become promising candidates for MPS. Realization of these photovoltaic MPS (PV-MPS) with unconventionally extraordinary attributes requires new 'out-of-box' designs. Natural materials have provided promising designing solutions to engineer properties under a broad range of boundary conditions, ranging from molecules, proteins, cells, tissues, apparatus to systems in animals, plants, and humans optimized through billions of years of evolution. Applying bio-inspired strategies in PV-MPS could be biomolecular modification on crystallization at the atomic/meso-scale, bio-structural duplication at the device/system level and bio-mimicking at the functional level to render efficient charge delivery, energy transport/utilization, as well as stronger resistance against environmental stimuli (e.g., self-healing and self-cleaning). In this review, we discuss the bio-inspired/-mimetic structures, experimental models, and working principles, with the goal of revealing physics and bio-microstructures relevant for PV-MPS. Here the emphasis is on identifying the strategies and material designs towards improvement of the performance of emerging halide perovskite PVs and strategizing their bridge to future MPS.

Photosynthetic Nanomaterial Hybrids for Bioelectricity and Renewable Energy Systems

Harvesting solar energy in the form of electricity from the photosynthesis of plants, algal cells, and bacteria has been researched as the most environment-friendly renewable energy technology in the last decade. The primary challenge has been the engineering of electrochemical interfacing with photosynthetic apparatuses, organelles, or whole cells. However, with the aid of low-dimensional nanomaterials, there have been many advances, including enhanced photon absorption, increased generation of photosynthetic electrons (PEs), and more efficient transfer of PEs to electrodes. These advances have demonstrated the possibility for the technology to advance to a new level. In this article, the fundamentals of photosynthesis are introduced. How PE harvesting systems have improved concerning solar energy absorption, PE production, and PE collection by electrodes is discussed. The review focuses on how different kinds of nanomaterials are applied and function in interfacing with photosynthetic materials for enhanced PE harvesting. Finally, the review analyzes how the performance of PE harvesting and stand-alone systems have evolved so far and its future prospects.

Supercapacitive biofuel cells

Supercapacitive biofuel cells' (SBFCs) most recent advancements are herein disclosed. In conventional SBFCs the biocomponent is employed as the pseudocapacitive component, while in self-charging biodevices it also works as the biocatalyst. The performance of different types of SBFCs are summarized according to the categorization based on the biocatalyst employed: supercapacitive microbial fuel cells (s-MFCs), supercapacitive biophotovoltaics (SBPV) and supercapacitive enzymatic fuel cells (s-EFCs). SBFCs could be considered as promising 'alternative' energy devices (low-cost, environmentally friendly, and technically undemanding electric power sources etc.) being suitable for powering a new generation of miniaturized electronic applications.

Photopolymerization performed under dark conditions using long-stored electrons in carbon nitride

In nature, the chemical energy and electrons stored in ATP and NADPH generated during irradiation can facilitate biochemical reactions under dark conditions. However, in artificial photoreaction systems, it is still very difficult to perform photoreactions under dark conditions due to the fact that the photogenerated charge pairs can recombine immediately upon ceasing the irradiation. Preventing the recombination of photogenerated charge pairs still constitutes a major challenge at present. Here, it is reported that functionalized carbon nitride nanomaterials having many heptazine rings with a positive charge distribution, which can tightly trap photogenerated electrons, efficiently prevent the recombination of photogenerated charges. These stored charges are exceedingly long-lived (up to months) and can drive photopolymerization without light irradiation, even after one month. The system introduced here demonstrates a new approach for storing light energy as long-lived radicals, enabling photoreactions under dark conditions.

Indium Tin Oxide Branched Nanowire and Poly(3-hexylthiophene) Hybrid Structure for a Photorechargeable Supercapacitor

We report a photorechargeable supercapacitor that can convert solar energy to chemical energy and store it. The supercapacitor is composed of indium tin oxide branched nanowires (ITO BRs) and poly(3-hexylthiophene) (P3HT) semiconducting polymers. ITO BRs showed electrical double layer capacitive characteristics that originated from the unique porous and self-connected network structure. The hybrid structure of ITO BR/P3HT exhibited spontaneous light harvesting, energy conversion, and charge storage. As a result, photocharging/discharging of ITO BR/P3HT showed an areal capacitance of 2.44 mF/cm² at a current density of 0.02 mA/cm². The proof-of-concept photorechargeable device, composed of ITO BRs, ITO BR/P3HT, and Na₂SO₄/polyvinyl acetate gel electrolyte, generated a photovoltage as high as 0.28 V and stored charge effectively for tens of seconds. The combination of dual functions in a single hybrid material may achieve breakthrough advances.

Shadow enhanced self-charging power system for wave and solar energy harvesting from the ocean

Hybrid energy-harvesting systems that capture both wave and solar energy from the oceans using triboelectric nanogenerators and photovoltaic cells are promising renewable energy solutions. However, ubiquitous shadows cast from moving objects in these systems are undesirable as they degrade the performance of the photovoltaic cells. Here we report a shadow-tribo-effect nanogenerator that hybrids tribo-effect and shadow-effect together to overcome this issue. Several fiber-supercapacitors are integrated with the shadow-tribo-effect nanogenerator to form a self-charging power system. To capture and store wave/solar energy from oceans, an energy ball based on the self-charging power system is demonstrated. By harnessing the shadow-effect, i.e. the shadow of the moving object in the energy ball, the charging time shortens to 253.3 s to charge the fiber-supercapacitors to the same voltage (0.3 V) as using pure tribo-effect. This cost-effective method to harvest and store the wave/solar energy from the oceans in this work is expected to inspire next-generation large-scale blue energy harvesting.

Ubiquitous shadows cast from moving objects in hybrid energy-harvesting systems are undesirable as they degrade the performance of the photovoltaic cells. Here the authors report the shadow of the moving object in a hybrid energy-harvesting system shortens charging time to charge a self-charging power system.

Primary electron transfer in Rhodobacter sphaeroides R-26 reaction centers under dehydration conditions

The photoinduced charge separation in Q_B-depleted reaction centers (RCs) from Rhodobacter sphaeroides R-26 in solid air-dried and vacuum-dried (~10^-2 Torr) films, obtained in the presence of detergent n-dodecyl-β-D-maltoside (DM), is characterized using ultrafast transient absorption spectroscopy. It is shown that drying of RC-DM complexes is accompanied by reversible blue shifts of the ground-state absorption bands of the pigment ensemble, which suggest that no dehydration-induced structural destruction of RCs occurs in both types of films. In air-dried films, electron transfer from the excited primary electron donor P^⁎ to the photoactive bacteriopheophytin H_A proceeds in 4.7 ps to form the P⁺H_A^- state with essentially 100% yield. P⁺H_A^- decays in 260 ps both by electron transfer to the primary quinone Q_A to give the state P⁺Q_A^- (87% yield) and by charge recombination to the ground state (13% yield). In vacuum-dried films, P^⁎ decay is characterized by two kinetic components with time constants of 4.1 and 46 ps in a proportion of ~55%/45%, and P⁺H_A^- decays about 2-fold slower (462 ps) than in air-dried films. Deactivation of both P^⁎ and P⁺H_A^- to the ground state effectively competes with the corresponding forward electron-transfer reactions in vacuum-dried RCs, reducing the yield of P⁺Q_A^- to 68%. The results are compared with the data obtained for fully hydrated RCs in solution and are discussed in terms of the presence in the RC complexes of different water molecules, the removal/displacement of which affects spectral properties of pigment cofactors and rates and yields of the electron-transfer reactions.

Analysis of Photosynthetic Systems and Their Applications with Mathematical and Computational Models

In biological and life science applications, photosynthesis is an important process that involves the absorption and transformation of sunlight into chemical energy. During the photosynthesis process, the light photons are captured by the green chlorophyll pigments in their photosynthetic antennae and further funneled to the reaction center. One of the most important light harvesting complexes that are highly important in the study of photosynthesis is the membrane-attached Fenna–Matthews–Olson (FMO) complex found in the green sulfur bacteria. In this review, we discuss the mathematical formulations and computational modeling of some of the light harvesting complexes including FMO. The most recent research developments in the photosynthetic light harvesting complexes are thoroughly discussed. The theoretical background related to the spectral density, quantum coherence and density functional theory has been elaborated. Furthermore, details about the transfer and excitation of energy in different sites of the FMO complex along with other vital photosynthetic light harvesting complexes have also been provided. Finally, we conclude this review by providing the current and potential applications in environmental science, energy, health and medicine, where such mathematical and computational studies of the photosynthesis and the light harvesting complexes can be readily integrated.

Enhanced Biophotocurrent Generation in Living Photosynthetic Optical Resonator

Bioenergy from photosynthetic living organisms is a potential solution for energy-harvesting and bioelectricity-generation issues. With the emerging interest in biophotovoltaics, extracting electricity from photosynthetic organisms remains challenging because of the low electron-transition rate and photon collection efficiency due to membrane shielding. In this study, the concept of "photosynthetic resonator" to amplify biological nanoelectricity through the confinement of living microalgae (Chlorella sp.) in an optical micro/nanocavity is demonstrated. Strong energy coupling between the Fabry-Perot cavity mode and photosynthetic resonance offers the potential of exploiting optical resonators to amplify photocurrent generation as well as energy harvesting. Biomimetic models and living photosynthesis are explored in which the power is increased by almost 600% and 200%, respectively. Systematic studies of photosystem fluorescence and photocurrent are simultaneously carried out. Finally, an optofluidic-based photosynthetic device is developed. It is envisaged that the key innovations proposed in this study can provide comprehensive insights in biological-energy sciences, suggesting a new avenue to amplify electrochemical signals using an optical cavity. Promising applications include photocatalysis, photoelectrochemistry, biofuel devices, and sustainable optoelectronics.

Introduction of the Menaquinone Biosynthetic Pathway into Rhodobacter sphaeroides and de Novo Synthesis of Menaquinone for Incorporation into Heterologously Expressed Integral Membrane Proteins

Quinones are redox-active molecules that transport electrons and protons in organelles and cell membranes during respiration and photosynthesis. In addition to the fundamental importance of these processes in supporting life, there has been considerable interest in exploiting their mechanisms for diverse applications ranging from medical advances to innovative biotechnologies. Such applications include novel treatments to target pathogenic bacterial infections and fabricating biohybrid solar cells as an alternative renewable energy source. Ubiquinone (UQ) is the predominant charge-transfer mediator in both respiration and photosynthesis. Other quinones, such as menaquinone (MK), are additional or alternative redox mediators, for example in bacterial photosynthesis of species such as Thermochromatium tepidum and Chloroflexus aurantiacus. Rhodobacter sphaeroides has been used extensively to study electron transfer processes, and recently as a platform to produce integral membrane proteins from other species. To expand the diversity of redox mediators in R. sphaeroides, nine Escherichia coli genes encoding the synthesis of MK from chorismate and polyprenyl diphosphate were assembled into a synthetic operon in a newly designed expression plasmid. We show that the menFDHBCE, menI, menA, and ubiE genes are sufficient for MK synthesis when expressed in R. sphaeroides cells, on the basis of high performance liquid chromatography and mass spectrometry. The T. tepidum and C. aurantiacus photosynthetic reaction centers produced in R. sphaeroides were found to contain MK. We also measured in vitro charge recombination kinetics of the T. tepidum reaction center to demonstrate that the MK is redox-active and incorporated into the Q_A pocket of this heterologously expressed reaction center.

Pulsed Force Kelvin Probe Force Microscopy

Measurement of the contact potential difference (CPD) and work functions of materials are important in analyzing their electronic structures and surface residual charges. Kelvin probe force microscopy (KPFM), an imaging technique of atomic force microscopy, has been widely used for surface potential and work function mapping at the nanoscale. However, the conventional KPFM variants are often limited in their spatial resolution to 30-100 nm under ambient conditions. The continuingly decreasing size and increasing complexity of photoactive materials and semiconductor devices will present future challenges in uncovering their nanometer-scale electrical properties through KPFM. Here, we introduce a KPFM technique based on the pulsed force mode of atomic force microscopy. Our technique, named pulsed force Kelvin Probe Force Microscopy (PF-KPFM), is a single-pass technique that utilizes the intrinsic Fermi level alignment between the AFM tip and the conductive sample without the need for an external oscillating voltage. Induced cantilever oscillations generated by a spontaneous redistribution of electrons between tip and sample are extracted and used to obtain the cantilever oscillation amplitude and to derive the surface potential. The spatial resolution of PF-KPFM is shown to be <10 nm under ambient conditions. The high spatial resolution surface potential mapping enables in situ determination of ohmic and nonohmic contacts between metals and semiconductors, mapping boundaries of ferroelectric domains of BaTiO₃, as well as characterization of protein aggregates. High spatial resolution measurements with PF-KPFM will facilitate further studies directed at uncovering electrical properties for emerging photoactive materials, biological samples, and semiconductor devices.

Minding the Gap between Plant and Bacterial Photosynthesis within a Self-Assembling Biohybrid Photosystem

Many strategies for meeting mankind's future energy demands through the exploitation of plentiful solar energy have been influenced by the efficient and sustainable processes of natural photosynthesis. A limitation affecting solar energy conversion based on photosynthetic proteins is the selective spectral coverage that is the consequence of their particular natural pigmentation. Here we demonstrate the bottom-up formation of semisynthetic, polychromatic photosystems in mixtures of the chlorophyll-based LHCII major light harvesting complex from the oxygenic green plant Arabidopsis thaliana, the bacteriochlorophyll-based photochemical reaction center (RC) from the anoxygenic purple bacterium Rhodobacter sphaeroides and synthetic quantum dots (QDs). Polyhistidine tag adaptation of LHCII and the RC enabled predictable self-assembly of LHCII/RC/QD nanoconjugates, the thermodynamics of which could be accurately modeled and parametrized. The tricomponent biohybrid photosystems displayed enhanced solar energy conversion via either direct chlorophyll-to-bacteriochlorophyll energy transfer or an indirect pathway enabled by the QD, with an overall energy transfer efficiency comparable to that seen in natural photosystems.

Protein Biophotosensitizer-Based IGZO Photo-thin Film Transistors for Monitoring Harmful Ultraviolet Light

The development of health monitoring devices to prevent skin cancers or various diseases arising from exposure to harmful light has attracted increasing scientific interest and has led to the exploration of hybrid inorganic-biological systems through the incorporation of biomolecules. Here, ultraviolet (UV) photodetectors based on transistors incorporating green fluorescent protein (GFP) molecules on multilayer-stacked indium-gallium-zinc-oxide (IGZO) thin films are studied, where the top layer of the IGZO films has different surface properties. Light-sensitive GFP can play a role as a biophotosensitizer due to light-induced electron transfer during photoexcitation. Intriguingly, the IGZO photo-thin film transistors (TFTs) with GFP molecules on a relatively more hydrophilic surface (less defective surface) have better device performance and exhibit a dramatic decrease in the photocurrent after turning the UV light off compared to the cases without GFP molecules on the more hydrophilic surface and on the less hydrophilic surface (more defective surface). A physical mechanism based on energy band diagrams is proposed, and the light-induced threshold voltage shift in the IGZO photo-TFTs is estimated and explained in terms of oxygen-related vacancy sites and trap/interface conditions in the IGZO film and light-induced electron transfer from the GFP molecules.