From Dynamic Measurements of Photosynthesis in a Living Plant to Sunlight Transformation into Electricity

A perspective on plant robotics: from bioinspiration to hybrid systems

As miscellaneous as the Plant Kingdom is, correspondingly diverse are the opportunities for taking inspiration from plants for innovations in science and engineering. Especially in robotics, properties like growth, adaptation to environments, ingenious materials, sustainability, and energy-effectiveness of plants provide an extremely rich source of inspiration to develop new technologies-and many of them are still in the beginning of being discovered. In the last decade, researchers have begun to reproduce complex plant functions leading to functionality that goes far beyond conventional robotics and this includes sustainability, resource saving, and eco-friendliness. This perspective drawn by specialists in different related disciplines provides a snapshot from the last decade of research in the field and draws conclusions on the current challenges, unanswered questions on plant functions, plant-inspired robots, bioinspired materials, and plant-hybrid systems looking ahead to the future of these research fields.

Plant Bioelectronics and Biohybrids: The Growing Contribution of Organic Electronic and Carbon-Based Materials

Life in our planet is highly dependent on plants as they are the primary source of food, regulators of the atmosphere, and providers of a variety of materials. In this work, we review the progress on bioelectronic devices for plants and biohybrid systems based on plants, therefore discussing advancements that view plants either from a biological or a technological perspective, respectively. We give an overview on wearable and implantable bioelectronic devices for monitoring and modulating plant physiology that can be used as tools in basic plant science or find application in agriculture. Furthermore, we discuss plant-wearable devices for monitoring a plant's microenvironment that will enable optimization of growth conditions. The review then covers plant biohybrid systems where plants are an integral part of devices or are converted to devices upon functionalization with smart materials, including self-organized electronics, plant nanobionics, and energy applications. The review focuses on advancements based on organic electronic and carbon-based materials and discusses opportunities, challenges, as well as future steps.

Biohybrid generators based on living plants and artificial leaves: influence of leaf motion and real wind outdoor energy harvesting

Plants translate wind energy into leaf fluttering and branch motion by reversible tissue deformation. Simultaneously, the outermost structure of the plant, i.e. the dielectric cuticula, and the inner ion-conductive tissue can be used to convert mechanical vibration energy, such as that produced during fluttering in the wind, into electricity by surface contact electrification and electrostatic induction. Constraining a tailored artificial leaf to a plant leaf can enhance oscillations and transient mechanical contacts and thereby increase the electricity outcome. We have studied the effects of wind-induced mechanical interactions between the leaf of a plant (Rhododendron) and a flexible silicone elastomer-based artificial leaf fixed at the petiole on power output and whether performance can be further tuned by altering the vibrational behavior of the artificial leaf. The latter is achieved by modifying a concentrated mass at the tip of the artificial leaf and observing plant-generated current and voltage signals under air flow. In this configuration, the plant-hybrid wind-energy converters can directly power light-emitting diodes and a temperature sensor. Detailed output analysis has revealed that, under all conditions, an increase in wind speed leads to nearly linearly increased voltages and currents. Accordingly, the cumulative sum energy reaches its highest values at the highest wind speed and resulting oscillations of the plant-artificial leaf system. The mass at the tip can, in most cases, be used to increase the voltage amplitude and frequency. Nevertheless, this behavior was found to depend on the individual configuration of the system, such as the leaf morphology. Analysis of these factors under controlled conditions is crucial for optimizing systems meant to operate in unstructured outdoor scenarios. We have established, in a first approach, that the artificial leaf-plant hybrid generator is capable of autonomously generating electricity outdoors under real outdoor wind conditions, even at a low average wind speed of only 1.9 m s^-1.

Energy Harvesting Strategies for Wireless Sensor Networks and Mobile Devices: A Review

Wireless sensor network nodes and mobile devices are normally powered by batteries that, when depleted, must be recharged or replaced. This poses important problems, in particular for sensor nodes that are placed in inaccessible areas or biomedical sensors implanted in the human body where the battery replacement is very impractical. Moreover, the depleted battery must be properly disposed of in accordance with national and international regulations to prevent environmental pollution. A very interesting alternative to power mobile devices is energy harvesting where energy sources naturally present in the environment (such as sunlight, thermal gradients and vibrations) are scavenged to provide the power supply for sensor nodes and mobile systems. Since the presence of these energy sources is discontinuous in nature, electronic systems powered by energy harvesting must include a power management system and a storage device to store the scavenged energy. In this paper, the main strategies to design a wireless mobile sensor system powered by energy harvesting are reviewed and different sensor systems powered by such energy sources are presented.

Materials Strategies and Device Architectures of Emerging Power Supply Devices for Implantable Bioelectronics

Implantable bioelectronics represent an emerging technology that can be integrated into the human body for diagnostic and therapeutic functions. Power supply devices are an essential component of bioelectronics to ensure their robust performance. However, conventional power sources are usually bulky, rigid, and potentially contain hazardous constituent materials. The fact that biological organisms are soft, curvilinear, and have limited accommodation space poses new challenges for power supply systems to minimize the interface mismatch and still offer sufficient power to meet clinical-grade applications. Here, recent advances in state-of-the-art nonconventional power options for implantable electronics, specifically, miniaturized, flexible, or biodegradable power systems are reviewed. Material strategies and architectural design of a broad array of power devices are discussed, including energy storage systems (batteries and supercapacitors), power devices which harvest sources from the human body (biofuel cells, devices utilizing biopotentials, piezoelectric harvesters, triboelectric devices, and thermoelectric devices), and energy transfer devices which utilize sources in the surrounding environment (ultrasonic energy harvesters, inductive coupling/radiofrequency energy harvesters, and photovoltaic devices). Finally, future challenges and perspectives are given.

Implantable Energy-Harvesting Devices

The sustainable operation of implanted medical devices is essential for healthcare applications. However, limited battery capacity is a key challenge for most implantable medical electronics (IMEs). The human body abounds with mechanical and chemical energy, such as the heartbeat, breathing, blood circulation, and the oxidation-reduction of glucose. Harvesting energy from the human body is a possible approach for powering IMEs. Many new methods for developing in vivo energy harvesters (IVEHs) have been proposed for powering IMEs. In this context energy harvesters based on the piezoelectric effect, triboelectric effect, automatic wristwatch devices, biofuel cells, endocochlear potential, and light, with an emphasis on fabrication, energy output, power management, durability, animal experiments, evaluation criteria, and typical applications are discussed. Importantly, the IVEHs that are discussed, are actually implanted into living things. Future challenges and perspectives are also highlighted.

Enhancement of Power Output by using Alginate Immobilized Algae in Biophotovoltaic Devices

We report for the first time a photosynthetically active algae immobilized in alginate gel within a fuel cell design for generation of bioelectricity. The algal-alginate biofilm was utilized within a biophotovoltaics (BPV) device developed for direct bioelectricity generation from photosynthesis. A peak power output of 0.289 mWm-2 with an increase of 18% in power output compared to conventional suspension culture BPV device was observed. The increase in maximum power density was correlated to the maximum relative electron transport rate (rETRm). The semi-dry type of photosynthetically active biofilm proposed in this work may offer significantly improved performances in terms of fuel cell design, bioelectricity generation, oxygen production and CO2 reduction.

Novel microbial photobioelectrochemical cell using an invasive ultramicroelectrode array and a microfluidic chamber

OBJECTIVE

To fabricate a novel microbial photobioelectrochemical cell using silicon microfabrication techniques.

RESULTS

High-density photosynthetic cells were immobilized in a microfluidic chamber, and ultra-microelectrodes in a microtip array were inserted into the cytosolic space of the cells to directly harvest photosynthetic electrons. In this way, the microbial photobioelectrochemical cell operated without the aid of electron mediators. Both short circuit current and open circuit voltage of the microbial photobioelectrochemical cell responded to light stimuli, and recorded as high as 250 pA and 45 mV, respectively.

CONCLUSION

A microbial photobioelectrochemical cell was fabricated with potential use in next-generation photosynthesis-based solar cells and sensors.

Bioelectrocatalytic NAD+/NADH inter-conversion: transformation of an enzymatic fuel cell into an enzymatic redox flow battery

Diaphorase and a benzylpropylviologen redox polymer were combined to create a bioelectrode that can both oxidize NADH and reduce NAD⁺.

Data Acquisition System for In Situ Monitoring of Chemoelectrical Potential in Living Plant Fuel Cells

Photosynthesis process in plants generates numerous sources of bioenergy. However, only a small fraction is readily exploited for electrical energy. The impact of environmental factors is one of the significant physiological influences on the electrical potential of the plants. Hence, we developed a data acquisition (DAQ) system for instantaneous monitoring of electrical potential in plants and Aloe vera was used as a plant sample. The static response characterization, capability index (P/T), and Pearson's coefficient of correlation procedures were applied to assess the reliability of the obtained data. This developed system offers the capability of in situ monitoring and detecting gradual changes in the electrical potential of plants up to a correlational strength of greater than 0.7. Interpretation of the electrical signal mechanisms in the Aloe vera plant and the optimization of the electricity can be achieved through the application of this monitoring system. This system, therefore, can serve as a tool to measure and analyze the electrical signals in plants at different conditions.

Design of a mediated enzymatic fuel cell to generate power from renewable fuel sources

The present work reported a compartment-less enzymatic fuel cell (EFC) based on newly synthesized Poly(pyrrole-2-carboxylic acid-co-3-thiophene acetic acid) film containing glucose oxidase and laccase effectively wired by p-benzoquinone incorporated into the copolymer structure. The resulting system generated a power density of 18.8 µW/cm(2) with 30 mM of glucose addition at +0.94 V at room temperature. Improvements to maximize the power output were ensured with step-by-step optimization of electrode fabrication design and operational parameters for operating the system with renewable fuel sources. We demonstrated that the improved fuel cell could easily harvest glucose produced during photosynthesis to produce electrical energy in a simple, renewable and sustainable way by generating a power density of 10 nW/cm(2) in the plant leaf within 2 min. An EFC for the first time was successfully operated in municipal wastewater which contained glycolytic substances to generate electrical energy with a power output of 3.3 µW/cm(2).

Reduced graphene oxide anodes for potential application in algae biophotovoltaic platforms

The search for renewable energy sources has become challenging in the current era, as conventional fuel sources are of finite origins. Recent research interest has focused on various biophotovoltaic (BPV) platforms utilizing algae, which are then used to harvest solar energy and generate electrical power. The majority of BPV platforms incorporate indium tin oxide (ITO) anodes for the purpose of charge transfer due to its inherent optical and electrical properties. However, other materials such as reduced graphene oxide (RGO) could provide higher efficiency due to their intrinsic electrical properties and biological compatibility. In this work, the performance of algae biofilms grown on RGO and ITO anodes were measured and discussed. Results indicate improved peak power of 0.1481 mWm⁻² using the RGO electrode and an increase in efficiency of 119%, illustrating the potential of RGO as an anode material for applications in biofilm derived devices and systems.

Development and operation of gold and cobalt oxide nanoparticles containing polypropylene based enzymatic fuel cell for renewable fuels

Newly synthesized gold and cobalt oxide nanoparticle embedded Polypropylene-g-Polyethylene glycol was used for a compartment-less enzymatic fuel cell. Glucose oxidase and bilirubin oxidase were selected as anodic and cathodic enzymes, respectively. Electrode fabrication and EFC operation parameters were optimized to achieve high power output. Maximum power density of 23.5 µW cm(-2) was generated at a cell voltage of +560 mV vs Ag/AgCl, in 100mM PBS pH 7.4 with the addition of 20mM of synthetic glucose solution. 20 µg of polymer amount with 185 µg of glucose oxidase and 356 µg of bilirubin oxidase was sufficient to get maximum performance. The working electrodes could harvest glucose, produced during photosynthesis reaction of Carpobrotus Acinaciformis plant, and readily found in real domestic wastewater of Zonguldak City in Turkey.

Emulsion-templated macroporous carbons synthesized by hydrothermal carbonization and their application for the enzymatic oxidation of glucose

Carbon-based monoliths have been designed using a simple synthetic pathway based on using high internal phase emulsion (HIPE) as a soft template to confine the polymerization and hydrothermal carbonization of saccharide derivatives (furfural) and phenolic compounds (phloroglucinol). Monosaccharides can be isolated from the cellulosic fraction of lignocellulosic biomass and phloroglucinol can be extracted from the bark of fruit trees; however, this approach constitutes an interesting sustainable synthetic route. The macroscopic characteristics can be easily modulated; a high macroporosity and total pore volume of up to 98 % and 18 cm(3)g(-1) have been obtained, respectively. After further thermal treatment under inert atmosphere, the as-synthesized macroporous carbonized HIPEs (carbo-HIPEs) have shaping capabilities relating to interesting mechanical properties as well as a high electrical conductivity of up to 300 Sm(-1) . These conductive foams exhibit a hierarchical structure associated with the presence of both meso- and micropores that exhibit specific Brunauer-Emmett-Teller (BET) surface areas and DFT total pore volumes up to 730 m(2)g(-1) and 0.313 cm(3)g(-1) , respectively. Because of their attractive structural characteristics and intrinsic properties, these macroporous monoliths have been incorporated as a proof of principle within electrochemical devices as modified thin carbon disc electrodes. A promising two-fold improvement in the catalytic current is observed for the electrooxidation of glucose after the immobilization of a glucose oxidase-based biocatalytic mixture onto the carbo-HIPE electrodes compared to that observed if using commercial glassy carbon electrodes.

Biofuel cells: enhanced enzymatic bioelectrocatalysis

Enzymatic biofuel cells represent an emerging technology that can create electrical energy from biologically renewable catalysts and fuels. A wide variety of redox enzymes have been employed to create unique biofuel cells that can be used in applications such as implantable power sources, energy sources for small electronic devices, self-powered sensors, and bioelectrocatalytic logic gates. This review addresses the fundamental concepts necessary to understand the operating principles of biofuel cells, as well as recent advances in mediated electron transfer- and direct electron transfer-based biofuel cells, which have been developed to create bioelectrical devices that can produce significant power and remain stable for long periods.

Bilirubin oxidase from Magnaporthe oryzae: an attractive new enzyme for biotechnological applications

A novel bilirubin oxidase (BOD), from the rice blast fungus Magnaporthe oryzae, has been identified and isolated. The 64-kDa protein containing four coppers was successfully overexpressed in Pichia pastoris and purified to homogeneity in one step. Protein yield is more than 100 mg for 2 L culture, twice that of Myrothecium verrucaria. The k(cat)/K(m) ratio for conjugated bilirubin (1,513 mM⁻¹ s⁻¹) is higher than that obtained for the BOD from M. verrucaria expressed in native fungus (980 mM⁻¹ s⁻¹), with the lowest K(m) measured for any BOD highly desirable for detection of bilirubin in medical samples. In addition, this protein exhibits a half-life for deactivation >300 min at 37 °C, high stability at pH 7, and high tolerance towards urea, making it an ideal candidate for the elaboration of biofuel cells, powering implantable medical devices. Finally, this new BOD is efficient in decolorizing textile dyes such as Remazol brilliant Blue R, making it useful for environmentally friendly industrial applications.

Mediatorless high-power glucose biofuel cells based on compressed carbon nanotube-enzyme electrodes

Enzymatic fuel cells use enzymes to produce energy from bioavailable substrates. However, such biofuel cells are limited by the difficult electrical wiring of enzymes to the electrode. Here we show the efficient wiring of enzymes in a conductive pure carbon nanotube matrix for the fabrication of a glucose biofuel cell (GBFC). Glucose oxidase and laccase were respectively incorporated in carbon nanotube disks by mechanical compression. The characterization of each bioelectrode shows an open circuit potential corresponding to the redox potential of the respective enzymes, and high current densities for glucose oxidation and oxygen reduction. The mediatorless GBFC delivers a high power density up to 1.3 mW cm⁻² and an open circuit voltage of 0.95 V. Moreover, the GBFC remains stable for 1 month and delivers 1 mW cm⁻² power density under physiological conditions (5×10⁻³ mol l⁻¹glucose, pH 7). To date, these values are the best performances obtained for a GBFC.

Glucose biofuel cells can be used to produce clean energy from renewable sources, but their use is limited by poor stability and low power output. In this study, bioelectrodes are fabricated using carbon nanotubes and the resulting biofuel cells have improved stability and power.

Efficient direct electron transfer of PQQ-glucose dehydrogenase on carbon cryogel electrodes at neutral pH

We present a comprehensive study of the direct electron transfer reaction of soluble PQQ-GDH from Acinetobacter calcoaceticus. Wild-type PQQ-sGDH nonspecifically adsorbed on carbon cryogel electrodes retained its enzymatic activity for glucose and maltose oxidation at pH 7.2 and 37 °C. The cyclic voltammograms in the absence of enzymatic substrate showed 2 redox peaks that suggest a two-step, one-electron oxidation/reduction of PQQ. Calibration curves showed a linear amperometric response for a wide glucose concentration range, including the values normally found in blood. At saturation, the catalytic current reached 0.93 mA cm(-2). Altogether the experimental results suggest that the amperometric output of the electrodes and the shape of the calibration curves represent a combination of the intrinsic enzyme kinetics, the maximum rate of heterogeneous electron transfer and the substrate accessibility to the enzyme's active center caused by the confinement of the enzyme into the mesoporous structure. A new mutant enzyme, N428C, developed in our group that shows almost twice the maximum catalytic activity in homogeneous experiments in solution, also showed a DET signal on carbon cryogel electrodes for glucose electro-oxidation. The higher activity for the mutant enzyme was also verified on the electrode surface.

Signal transducers and enzyme cofactors are susceptible to oxidation by nanographite impurities in carbon nanotube materials

Carbon nanotubes (CNTs) are often employed in biofuel cells, artificial photosystems and bioelectronics in order to enhance electron transfer and to efficiently shuttle electrons between redox active molecules and the electrode surface. However, it should be noted that typical CNTs are highly heterogeneous materials, containing large amounts of impurities. Herein, we report the influence of nanographite impurities contained within CNTs upon the redox properties of signal transducers and enzyme cofactors that are vital for the functioning of biofuel cells, artificial leaves and bioelectronics as well as for the survival of living organisms. We investigate the susceptibility of tyrosine and tryptophan, amino acids involved in electron transfer and biorecognition reactions as well in the synthesis of neurotransmitters, in addition we also consider the susceptibility of the principal electron carrier β-nicotinamide adenine dinucleotide. We conclude that nanographite impurities within CNTs are responsible for the "electrocatalytic" oxidation of NADH and two amino acids involved in signal transduction, tyrosine and tryptophan. Our findings are of high importance for both industrial and biomedical applications.