Switchable aerobic/anaerobic multi-substrate biofuel cell operating on anodic and cathodic enzymatic cascade assemblies

Roots Fuel Cell Produces and Stores Clean Energy

In recent years, extensive scientific efforts have been conducted to develop clean bioenergy technologies. A promising approach that has been under development for more than a hundred years is the microbial fuel cell (MFC) which utilizes exoelectrogenic bacteria as an electron source in a bioelectrochemical cell. The viability of bacteria in soil MFCs can be maintained by integrating plant roots, which release organic materials that feed the bacteria. In this work, we show that rather than organic compounds, roots also release redox species that can produce electricity in a biofuel cell. We first studied the reduction of the electron acceptor Cytochrome C by green onion roots. We integrate green onion roots into a biofuel cell to produce a continuous bias-free electric current for more than 24 h in the dark. This current is enhanced upon irradiation of the onion's leaves with light. We apply cyclic voltammetry and 2D-fluorescence measurements to show that NADH and NADPH act as major electron mediators between the roots and the anode, while their concentrations in the external root matrix are increased upon irradiation of the leaves. Finally, we show that roots can contribute to energy storage by charging a supercapacitor.

Mammalian Fuel Cells Produce Electric Current

The increasing concern about climate change has led scientists around the world to develop clean energy technologies that may replace the traditional use of fossil fuels. A promising approach is the utilization of unicellular organisms as electron donors in bio-fuel cells. To date, this method has been limited to microorganisms such as bacteria, yeast, and microalgae. In this work, we show for the first time the concept of using mammalian cell cultures and organoids as electron donors in biofuel cells. We apply cyclic voltammetry to show that upon association of ARPE19 cells with the anode, they release reducing molecules to produce electricity. Furthermore, we apply 2D-fluorescence measurements and show that upon illumination, photosensitive stem cell-derived retinal organoids, which consist of rod photoreceptors and interneurons, secrete NADH and NADPH molecules that can donate electrons at the anode to produce photocurrent.

Photocurrent Production from Cherries in a Bio-Electrochemical Cell

In recent years, clean energy technologies that meet ever-increasing energy demands without the risk of environmental contamination has been a major interest. One approach is the utilization of plant leaves, which release redox-active NADPH as a result of photosynthesis, to generate photocurrent. In this work, we show for the first time that photocurrent can be harvested directly from the fruit of a cherry tree when associated with a bio-electrochemical cell. Furthermore, we apply electrochemical and spectroscopic methods to show that NADH in the fruit plays a major role in electric current production.

Direct Electricity Production from Nematostella and Arthemia's Eggs in a Bio-Electrochemical Cell

In recent years, extensive efforts have been made to develop clean energy technologies to replace fossil fuels to assist the struggle against climate change. One approach is to exploit the ability of bacteria and photosynthetic organisms to conduct external electron transport for electricity production in bio-electrochemical cells. In this work, we first show that the sea anemones Nematostella vectensis and eggs of Artemia (brine shrimp) secrete redox-active molecules that can reduce the electron acceptor Cytochrome C. We applied 2D fluorescence spectroscopy and identified NADH or NADPH as secreted species. Finally, we broaden the scope of living organisms that can be integrated with a bio-electrochemical cell to the sea anemones group, showing for the first time that Nematostella and eggs of Artemia can produce electrical current when integrated into a bio-electrochemical cell.

Harnessing photosynthesis to produce electricity using cyanobacteria, green algae, seaweeds and plants

The conversion of solar energy into electrical current by photosynthetic organisms has the potential to produce clean energy. Life on earth depends on photosynthesis, the major mechanism for biological conversion of light energy into chemical energy. Indeed, billions of years of evolution and adaptation to extreme environmental habitats have resulted in highly efficient light-harvesting and photochemical systems in the photosynthetic organisms that can be found in almost every ecological habitat of our world. In harnessing photosynthesis to produce green energy, the native photosynthetic system is interfaced with electrodes and electron mediators to yield bio-photoelectrochemical cells (BPECs) that transform light energy into electrical power. BPECs utilizing plants, seaweeds, unicellular photosynthetic microorganisms, thylakoid membranes or purified complexes, have been studied in attempts to construct efficient and non-polluting BPECs to produce electricity or hydrogen for use as green energy. The high efficiency of photosynthetic light-harvesting and energy production in the mostly unpolluting processes that make use of water and CO2 and produce oxygen beckons us to develop this approach. On the other hand, the need to use physiological conditions, the sensitivity to photoinhibition as well as other abiotic stresses, and the requirement to extract electrons from the system are challenging. In this review, we describe the principles and methods of the different kinds of BPECs that use natural photosynthesis, with an emphasis on BPECs containing living oxygenic photosynthetic organisms. We start with a brief summary of BPECs that use purified photosynthetic complexes. This strategy has produced high-efficiency BPECs. However, the lifetimes of operation of these BPECs are limited, and the preparation is laborious and expensive. We then describe the use of thylakoid membranes in BPECs which requires less effort and usually produces high currents but still suffers from the lack of ability to self-repair damage caused by photoinhibition. This obstacle of the utilization of photosynthetic systems can be significantly reduced by using intact living organisms in the BPEC. We thus describe here progress in developing BPECs that make use of cyanobacteria, green algae, seaweeds and higher plants. Finally, we discuss the future challenges of producing high and longtime operating BPECs for practical use.

DNA derived N-doped 3D conductive network with enhanced electrocatalytic activity and stability for membrane-less biofuel cells

Enzymes are promising electrocatalysts in many biological processes. We proposed two strategies, co-immobilization and three-dimensional (3D) space design, to strengthen electron transfer (ET). In this research, DNA base and CNT were mixed in an aqueous solution; then the mixture was dried and ground. Finally, the powder was annealed in N₂ to obtain DNA derived N-doped 3D conductive network (N-G@CNT). N-G@CNT immobilized mediators on itself through adsorption. Such 3D space structure shows high activity toward a set of critical electrochemical reactions and high-performance in enzymatic biofuel cells (EBFCs). It is found that N-G@CNT conductive network possesses an interconnected porous structure and well-developed porosity. As a result, the membrane-less EBFCs equipped with enzyme/mediator co-immobilization N-G@CNT bioelectrodes were measured in a model 5 mM glucose-containing aqueous solution, human serum, and rabbit whole blood, respectively, which can generate 0.34, 0.078, and 0.15 mW cm^-2 power density, respectively. The constant-current discharge method carried out in a model 5 mM glucose-containing aqueous solution shows that the discharge time reached 19 h at a discharge current density of 0.01 mA cm^-2. The membrane EBFCs can deliver a high open circuit voltage of 0.68 V, a short-circuit current density of 2 mA cm^-2, and a maximum power density of 0.5 mW cm^-2.

Status Update on Bioelectrochemical Systems: Prospects for Carbon Electrode Design and Scale-Up

Bioelectrochemical systems (BES) employ enzymes, subcellular structures or whole electroactive microorganisms as biocatalysts for energy conversion purposes, such as the electrosynthesis of value-added chemicals and power generation in biofuel cells. From a bioelectrode engineering viewpoint, customizable nanostructured carbonaceous matrices have recently received considerable scientific attention as promising electrode supports due to their unique properties attractive to bioelectronics devices. This review demonstrates the latest advances in the application of nano- and micro-structured carbon electrode assemblies in BES. Specifically, in view of the gradual increase in the commercial applicability of these systems, we aim to address the stability and scalability of different BES designs and to highlight their potential roles in a circular bioeconomy.

Multi-Substrate Biofuel Cell Utilizing Glucose, Fructose and Sucrose as the Anode Fuels

A significant problem still exists with the low power output and durability of the bioelectrochemical fuel cells. We constructed a fuel cell with an enzymatic cascade at the anode for efficient energy conversion. The construction involved fabrication of the flow-through cell by three-dimensional printing. Gold nanoparticles with covalently bound naphthoquinone moieties deposited on cellulose/polypyrrole (CPPy) paper allowed us to significantly improve the catalysis rate, both at the anode and cathode of the fuel cell. The enzymatic cascade on the anode consisted of invertase, mutarotase, Flavine Adenine Dinucleotide (FAD)-dependent glucose dehydrogenase and fructose dehydrogenase. The multi-substrate anode utilized glucose, fructose, sucrose, or a combination of them, as the anode fuel and molecular oxygen were the oxidant at the laccase-based cathode. Laccase was adsorbed on the same type of naphthoquinone modified gold nanoparticles. Interestingly, the naphthoquinone modified gold nanoparticles acted as the enzyme orienting units and not as mediators since the catalyzed oxygen reduction occurred at the potential where direct electron transfer takes place. Thanks to the good catalytic and capacitive properties of the modified electrodes, the power density of the sucrose/oxygen enzymatic fuel cells (EFC) reached 0.81 mW cm-2, which is beneficial for a cell composed of a single cathode and anode.

Cannabinoid Receptor Type 1 and Its Role as an Analgesic: An Opioid Alternative?

Understanding how the body regulates pain is fundamental to develop rational strategies to combat the growing prevalence of chronic pain states, opioid dependency, and the increased financial burden to the medical care system. Pain is the most prominent reason why Americans seek medical attention and extensive literature has identified the importance of the endocannabinoid pathway in controlling pain. Modulation of the endocannabinoid system offers new therapeutic opportunities for the selective control of excessive neuronal activity in several pain conditions (acute, inflammatory, chronic, and neuropathic). Cannabinoids have a long history of medicinal use and their analgesic properties are well documented; however, there are major impediments to understanding cannabinoid pain modulation. One major issue is the presence of psychotropic side effects associated with D9-tetrahydrocannabinol (THC) or synthetic derivatives, which puts an emphatic brake on their use. This dose-limiting effect prevents the appropriate degree of analgesia . Animal studies have shown that the psychotropic effects are mediated via brain cannabinoid type 1 (CB1) receptors, while analgesic activity in chronic pain states may be mediated via CB1R action in the spinal cord, brainstem, peripheral sensory neurons, or immune cells. The development of appropriate therapies is incumbent on our understanding of the role of peripheral versus central endocannabinoid-driven analgesia. Recent physiological, pharmacological, and anatomical studies provide evidence that one of the main roles of the endocannabinoid system is the regulation of gamma-aminobutyric acid (GABA) and/or glutamate release. This article will review this evidence in the context of its implications for pain. We first provide a brief overview of CB1R's role in the regulation of nociception, followed by a review of the evidence that the peripheral endocannabinoid system modulates nociception. We then look in detail at regulation of central-mediated analgesia, followed up with evidence that cannabinoidmediated modulation of pain involves modulation of GABAergic and glutamatergic neurotransmission in key brain regions. Finally, we discuss cannabinoid action on non-neuronal cells in the context of inflammation and direct modulation of neurons. This work stands to reveal long-standing controversies in the cannabinoid analgesia area that have had an impact on failed clinical trials and implementation of therapeutics targeting this system.

Magnetically induced enzymatic cascades - advancing towards multi-fuel direct/mediated bioelectrocatalysis

A generic method to magnetically assemble enzymatic cascades on electrode surfaces is introduced. The versatile method enables the simultaneous activation of both direct and mediated electron transfer bioelectrocatalysis to harness different substrates, which can serve as multiple fuels and oxidizers in biofuel cells generating clean energy.

Enzymatic self-wiring in nanopores and its application in direct electron transfer biofuel cells

A synthetic enzymatic activity in nanopores leading to the direct fabrication of modified electrodes applicable as biosensors and/or biofuel cell elements is reported. We demonstrate the heterogeneous enzymatic implanting of platinum nanoclusters, PtNCs, in glucose oxidase, GOx, immobilized on mesoporous carbon nanoparticles, MPCNP-modified surface. As the pores confine the growth of the clusters, the PtNC@GOx/MPCNP assembly becomes electrically wired to the matrix, demonstrating direct electron transfer, DET, bioelectrocatalytic properties that correlate with the applied duration of synthesis and cluster size. This inside-out nanocluster growth from the cofactor to the matrix is investigated and further compared to a reversed outside-in strategy which follows the electrochemical deposition of the Pt clusters inside the pores and their electrically induced expansion towards the FAD center of the enzyme. While the inside-out and outside-in methodologies provide, for the first time, synthetic bidirectional direct wiring routes of an enzyme to a surface, we highlight an asymmetry in the wiring efficiency associated with the different assemblies. The results indicate the existence of a shorter gap between the FAD cofactor and the PtNCs in the enzymatically implanted assembly, resulting in elevated bioelectrocatalytic currents, lower overpotential, and a higher turnover rate, 2580 e^- s^-1. The implanted assembly is then coupled to a bilirubin oxidase-adsorbed MPCNP cathode to yield an all-DET biofuel cell. Due to the superior electrical contact of the inside-out-synthesized anode, this cell demonstrates enhanced discharge potential and power outputs as compared to similar systems employing electrochemically synthesized outside-in-grown PtNC-GOx/MPCNPs or even GOx-modified MPCNPs diffusionally mediated by ferrocenemethanol.