Hybrid bio-organic interfaces with matchable nanoscale topography for durable high extracellular electron transfer activity

Unnatural Direct Interspecies Electron Transfer Enabled by Living Cell-Cell Click Chemistry

Direct interspecies electron transfer (DIET) is essential for maintaining the function and stability of anaerobic microbial consortia. However, only limited natural DIET modes have been identified and DIET engineering remains highly challenging. In this study, an unnatural DIET between Shewanella oneidensis MR-1 (SO, electron donating partner) and Rhodopseudomonas palustris (RP, electron accepting partner) was artificially established by a facile living cell-cell click chemistry strategy. By introducing alkyne- or azide-modified monosaccharides onto the cell outer surface of the target species, precise covalent connections between different species in high proximity were realized through a fast click chemistry reaction. Remarkably, upon covalent connection, outer cell surface C-type cytochromes mediated DIET between SO and RP was achieved and identified, although this was never realized naturally. Moreover, this connection directly shifted the natural H2 mediated interspecies electron transfer (MIET) to DIET between SO and RP, which delivered superior interspecies electron exchange efficiency. Therefore, this work demonstrated a naturally unachievable DIET and an unprecedented MIET shift to DIET accomplished by cell-cell distance engineering, offering an efficient and versatile solution for DIET engineering, which extends our understanding of DIET and opens up new avenues for DIET exploration and applications.

Heterogeneous g-C3N4/polyaniline composites enhanced the conversion of organics into methane during anaerobic wastewater treatment

In this study, g-C3N4/PANI was prepared by in situ oxidative polymerization. Graphite-phase carbon nitride (g-C3N4) with surface defects was deposited onto the surface of conductive polyaniline (PANI) to form a p-n heterojunction. This construction aimed to create an efficient heterogeneous catalyst, increasing the surface defect level and active sites of the composite, and augmenting its capability to capture and transfer extracellular electrons under anaerobic conditions. This addresses the challenge of low efficiency in direct interspecies electron transfer between bacteria and archaea during anaerobic digestion for methane production. The results showed that the prepared g-C3N4/PANI increased the CH4 yield and CH4 production rate by 82% and 96%, respectively. Notably, the conductivity and XPS test results showed that the ratio of g-C3N4 to PANI was 0.15, and the composite exhibited favorable conductivity, with a uniform distribution of pyrrolic nitrogen, pyridinic nitrogen, and graphitic nitrogen, each accounting for approximately 30%. Furthermore, g-C3N4/PANI effectively enhanced the metabolic efficiency of intermediate products such as acetate and butyrate. Analysis of the microbial community structure revealed that g-C3N4/PANI led to a significant increase in the abundance of hydrogenotrophic methanogen Methanolinea (from 48% to 64%) and enriched Clostridium (a rise of 1%) with direct interspecies electron transfer capability. Microbial community function analysis demonstrated that the addition of g-C3N4/PANI boosted the activities of key enzymes involved in anaerobic digestion, including phosphate transacetylase (PTA), phospho-butyryl transferase (PTB), and NAD-independent lactate dehydrogenase (NNLD), by 47%, 135%, and 153%, respectively. This acceleration in enzymatic activity promoted the metabolism of acetyl-CoA, butyryl-CoA, and pyruvate. Additionally, the function of ABC transporters was enhanced, thereby improving the efficiency of material and energy exchange among microorganisms.

Light and Magnetism Orchestrating Aquatic Pollutant-Degradation Robots in Programmable Trajectories

Interfacial floating robots have promising applications in carriers, environmental monitoring, water treatment, and so on. Even though, engineering smart robots with both precisely efficient navigation and elimination of water pollutants in long term remains a challenge, as the superhydrophobicity greatly lowers resistance for aquatic motion while sacrificing chemical reactivity of the surface. Here, a pollutant-removing superhydrophobic robot integrated with well-assembled iron oxide-bismuth sulfide heterojunction composite minerals, which provide both light and magnetic propulsion, and the ability of catalytic degradation, is reported. The motion velocity of the robot reaches up to 51.9 mm s-1 within only 300 ms of acceleration under the orchestration of light, and brakes rapidly (≈200-300 ms) once turn off the light. And magnetism extends the robot to work in broad range of surface tensions in any programmable trajectory. Besides, purification of polluted water is efficiently achieved in situ and the degradation efficiency exhibits eightfold enhancements under the effect of light-triggered photothermal behavior coupled with magnetic induction, overcoming the dilemma of efficient motion with catalytic superhydrophobicity. This strategy developed here provides guidelines for the explorations of high-performance smart devices.

Enhanced transmembrane electron transfer in Shewanella oneidensis MR-1 using gold nanoparticles for high-performance microbial fuel cells

Low efficiency of extracellular electron transfer (EET) is a major bottleneck in developing high-performance microbial fuel cells (MFCs). Herein, we construct Shewanella oneidensis MR-1@Au for the bioanode of MFCs. Through performance recovery experiments of mutants, we proved that abundant Au nanoparticles not only tightly covered the bacteria surface, but were also distributed in the periplasm and cytoplasm, and even embedded in the outer and inner membranes of the cell. These Au nanoparticles could act as electron conduits to enable highly efficient electron transfer between S. oneidensis MR-1 and electrodes. Strikingly, the maximum power density of the S. oneidensis MR-1@Au bioanode reached up to 3749 mW m-2, which was 17.4 times higher than that with the native bacteria, reaching the highest performance yet reported in MFCs using Au or Au-based nanocomposites as the anode. This work elucidates the role of Au nanoparticles in promoting transmembrane and extracellular electron transfer from the perspective of molecular biology and electrochemistry, while alleviating bottlenecks in MFC performances.

Delivering Mechanical Stimulation to Cells: State of the Art in Materials and Devices Design

Biochemical signals, such as growth factors, cytokines, and transcription factors are known to play a crucial role in regulating a variety of cellular activities as well as maintaining the normal function of different tissues and organs. If the biochemical signals are assumed to be one side of the coin, the other side comprises biophysical cues. There is growing evidence showing that biophysical signals, and in particular mechanical cues, also play an important role in different stages of human life ranging from morphogenesis during embryonic development to maturation and maintenance of tissue and organ function throughout life. In order to investigate how mechanical signals influence cell and tissue function, tremendous efforts have been devoted to fabricating various materials and devices for delivering mechanical stimuli to cells and tissues. Here, an overview of the current state of the art in the design and development of such materials and devices is provided, with a focus on their design principles, and challenges and perspectives for future research directions are highlighted.

Advances in interfacial engineering for enhanced microbial extracellular electron transfer

The extracellular electron transfer (EET) efficiency between electroactive microbes (EAMs) and electrode is a key factor determining the development of microbial electrochemical technology (MET). Currently, the low EET efficiency of EAMs limits the application of MET in the fields of organic matter degradation, electric energy production, seawater desalination, bioremediation and biosensing. Enhancement of the interaction between EAMs and electrode by interfacial engineering methods brings bright prospects for the improvement of the EET efficiency of EAMs. In view of the research in recent years, this mini-review systematically summarizes various interfacial engineering strategies ranging from electrode surface modification to hybrid biofilm formation, then to single cell interfacial engineering and intracellular reformation for promoting the electron transfer between EAMs and electrode, focusing on the applicability and limitations of these methodologies. Finally, the possible key directions, challenges and opportunities for future interfacial engineering to strengthen the microbial EET are proposed in this mini-review.

Current Progress of Interfacing Organic Semiconducting Materials with Bacteria

Microbial bioelectronics require interfacing microorganisms with electrodes. The resulting abiotic/biotic platforms provide the basis of a range of technologies, including energy conversion and diagnostic assays. Organic semiconductors (OSCs) provide a unique strategy to modulate the interfaces between microbial systems and external electrodes, thereby improving the performance of these incipient technologies. In this review, we explore recent progress in the field on how OSCs, and related materials capable of charge transport, are being used within the context of microbial systems, and more specifically bacteria. We begin by examining the electrochemical communication modes in bacteria and the biological basis for charge transport. Different types of synthetic organic materials that have been designed and synthesized for interfacing and interrogating bacteria are discussed next, followed by the most commonly used characterization techniques for evaluating transport in microbial, synthetic, and hybrid systems. A range of applications is subsequently examined, including biological sensors and energy conversion systems. The review concludes by summarizing what has been accomplished so far and suggests future design approaches for OSC bioelectronics materials and technologies that hybridize characteristic properties of microbial and OSC systems.

Nanomaterials Facilitating Microbial Extracellular Electron Transfer at Interfaces

Electrochemically active bacteria can transport their metabolically generated electrons to anodes, or accept electrons from cathodes to synthesize high-value chemicals and fuels, via a process known as extracellular electron transfer (EET). Harnessing of this microbial EET process has led to the development of microbial bio-electrochemical systems (BESs), which can achieve the interconversion of electrical and chemical energy and enable electricity generation, hydrogen production, electrosynthesis, wastewater treatment, desalination, water and soil remediation, and sensing. Here, the focus is on the current understanding of the microbial EET process occurring at both the bacteria-electrode interface and the biotic interface, as well as some attempts to improve the EET by using various nanomaterials. The behavior of nanomaterials in different EET routes and their influence on the performance of BESs are described. The inherent mechanisms will guide rational design of EET-related materials and lead to a better understanding of EET mechanisms.

Single cell electron collectors for highly efficient wiring-up electronic abiotic/biotic interfaces

By electronically wiring-up living cells with abiotic conductive surfaces, bioelectrochemical systems (BES) harvest energy and synthesize electric-/solar-chemicals with unmatched thermodynamic efficiency. However, the establishment of an efficient electronic interface between living cells and abiotic surfaces is hindered due to the requirement of extremely close contact and high interfacial area, which is quite challenging for cell and material engineering. Herein, we propose a new concept of a single cell electron collector, which is in-situ built with an interconnected intact conductive layer on and cross the individual cell membrane. The single cell electron collector forms intimate contact with the cellular electron transfer machinery and maximizes the interfacial area, achieving record-high interfacial electron transfer efficiency and BES performance. Thus, this single cell electron collector provides a superior tool to wire living cells with abiotic surfaces at the single-cell level and adds new dimensions for abiotic/biotic interface engineering.

Performance evaluation of treating oil-containing restaurant wastewater in microbial fuel cell using in situ graphene/polyaniline modified titanium oxide anode

Most studies conducted nowadays to boost electrode performance in microbial fuel cell (MFC) have focused on carbonaceous materials. The titanium suboxides (Ti₄O₇, TS) are able to provide a new alternative for achieving better performance in MFC and have been tested and demonstrated in this study. The Ti₄O₇ electrode with high electrochemical activity was modified by graphene/polyaniline by the constant potential method. Electrogenic microorganisms were more conducive to adhere to the anode electrode due to the presence of graphene/polyaniline. The MFC reactor with polyaniline /graphene modified TS (TSGP) anode achieves the highest voltage with 980 mV, and produces a peak power density of 2073 mW/m², which is 2.9 and 12.7 times of those with the carbon cloth anode, respectively, at the 1000 Ω external resistance. In addition, this study evaluates the effects of anolyte conductivity, pH, and COD on the treatment of oil-containing restaurant wastewater (OCRW) in MFC using TSGP anode. The OCRW amended with 120 mS/cm obtains the lowest internal resistance (160.3 Ω). Increasing the anodic pH, gradually from acidic (pH 5.5) to alkaline conditions (pH 8.0), resulted in a gradual increase in maximum power density to 576.4 mW/m² and a decrease in internal cell resistance to 203.7 Ω. The MFC at the COD 1500 mg/L could obtain steady-state output voltage during 103 h while removing up to 65.2% of the COD of the OCRW.

Vertical alignment of polyaniline nanofibers on electrode surface for high-performance microbial fuel cells

Electrode modifications with conductive and nanostructured polyaniline (PANI) were recognized as efficient approach to improve interaction between electrode surface and electrogenic bacteria for boosting the performance of microbial fuel cell (MFC). However, it still showed undesirable performance because of the challenge to control the orientation (such as vertical alignment) of PANI nanostructure for extracellular electron transfer (EET). In this work, vertically aligned polyaniline (VA-PANI) on carbon cloth electrode surface were prepared by in-situ polymerization method (simply tuning the ratio of tartaric acid (TA) dopant). Impressively, the VA-PANI greatly improved the EET due to the increased opportunity to connect with conductive proteins. Eventually, MFC equipped with the VA-PANI electrodes delivered a power output of 853 mW/m², which greatly outperformed those electrodes modified with un-oriented PANI. This work provided the possibility to control the orientation of PANI for EET and promise to harvest energy from wastewater with MFC.

Nanostructured interfaces for probing and facilitating extracellular electron transfer

Probing and facilitating microbial extracellular electron transfer through nanotechnology enabled platforms are transforming bioenergetic, bioelectronic, and other related research areas.

Improving the extracellular electron transfer of Shewanella oneidensis MR-1 for enhanced bioelectricity production from biomass hydrolysate

Direct electricity production from biomass hydrolysate by microbial fuel cells (MFC) holds great promise for the development of the sustainable biomass industry.

Facile One-Step Strategy for Highly Boosted Microbial Extracellular Electron Transfer of the Genus Shewanella

High performance of bacterial extracellular electron transfer (EET) is essentially important for its practical applications in versatile bioelectric fields. We developed a facile one-step approach to dramatically boost the bacterial EET activity 75-fold by exogenous addition of ethylenediamine tetraacetic acid disodium salt (EDTA-2Na, 1 mM) into the electrochemical cells, where the anodic process of microbial EET was monitored. We propose that EDTA-2Na enables both the alternation of the local environment around the c-type cytochromes located on the outer membrane channels (OMCs), which therefore changes the redox behavior of OMCs in mediating the EET process, and the formation of densely packed biofilm that can further facilitate the EET process. As a synergistic effect, the highly boosted bacterial EET activity was achieved. The method shows good generality for versatile bioelectrical bacteria. We envision that the method is also applicable for constructing various bioelectric devices.

Hydrophilicity boosted extracellular electron transfer in Shewanella loihica PV-4

A superhydrophilic electrode enables the drastically boosted bacterial EET activity ofShewanella loihicaPV-4. It is proposed that a hydrophilic electrode favors the reduced state of OMCs, and consequently both the EET activity and cell proliferation are highly facilitated.

Nanotechnology to rescue bacterial bidirectional extracellular electron transfer in bioelectrochemical systems

Advanced nanostructured electrode materials largely improve the bacterial bidirectional extracellular electron transfer in bioelectrochemical systems.

Facilitated extracellular electron transfer of Shewanella loihica PV-4 by antimony-doped tin oxide nanoparticles as active microelectrodes

Dissimilatory metal reducing bacteria are capable of extracellular electron transfer (EET) to insoluble metal oxides as external electron acceptors for their anaerobic respiration, which is recognized as an important energy-conversion process in natural and engineered environments, such as in mineral cycling, bioremediation, and microbial fuel/electrolysis cells. However, the low EET efficiency remains one of the major bottlenecks for its practical application. We report firstly that the microbial current generated by Shewanella loihica PV-4 (S. loihica PV-4) could be greatly improved that is up to ca. 115 fold, by adding antimony-doped tin oxide (ATO) nanoparticles in the electrochemical reactor. The results demonstrate that the biocompatible, electrically conductive ATO nanoparticles acted as active microelectrodes could facilitate the formation of a cells/ATO composite biofilm and the reduction of the outer membrane c-type cytochromes (OM c-Cyts) that are beneficial for the electron transfer from cells to electrode. Meanwhile, a synergistic effect between the participation of OM c-Cyts and the accelerated EET mediated by cell-secreted flavins may play an important role for the enhanced current generation in the presence of ATO nanoparticles. Moreover, it is worth noting that the TCA cycle in S. loihica PV-4 cells is activated by adding ATO nanoparticles, even if the potential is poised at +0.2 V, thereby also improving the EET process. The results presented here may provide a simple and effective strategy to boost the EET of S. loihica PV-4 cells, which is conducive to providing potential applications in bioelectrochemical systems.

Employing a Flexible and Low-Cost Polypyrrole Nanotube Membrane as an Anode to Enhance Current Generation in Microbial Fuel Cells

The flexible and low-cost polypyrrole nanotube membrane is demonstrated as a promising anode in microbial fuel cells, which significantly enhances the extracellular electron transfer between Shewanella oneidensis MR-1 and the electrode, owing to the large active surface area and high electrical conductivity.