Recent advances in microbial fuel cell-based self-powered biosensors: a comprehensive exploration of sensing strategies in both anode and cathode modes.

With the rapid development of society, it is of paramount importance to expeditiously assess environmental pollution and provide early warning of toxicity risks. Microbial fuel cell-based self-powered biosensors (MFC-SPBs) have emerged as a pivotal technology, obviating the necessity for external power sources and aligning with the prevailing trends toward miniaturization and simplification in biosensor development. In this case, vigorous advancements in MFC-SPBs have been acquired in past years, irrespective of whether the target identification event transpires at the anode or cathode. The present article undertakes a comprehensive review of developed MFC-SPBs, categorizing them into substrate effect and microbial activity effect based on the nature of the target identification event. Furthermore, various enhancement strategies to improve the analytical performance like accuracy and sensitivity are also outlined, along with a discussion of future research trends and application prospects of MFC-SPBs for their better developments.

Salts-assistant synthesis of g-C3N4/Prussian-blue analogue/nickel foam with hierarchical structures as binder-free electrodes for supercapacitors.

The exploitation of high-performance electrode materials is significant to develop supercapacitors with satisfied energy and power output properties. In this study, a g-C3N4/Prussian-blue analogue (PBA)/Nickel foam (NF) with hierarchical micro/nano structures was developed by a simple salts-directed self-assembly approach. In this synthetic strategy, NF acted as both 3D macroporous conductive substrate and Ni source for PBA formation. Moreover, the incidental salt in molten salt-synthesized g-C3N4 nanosheets could regulate the combination mode between g-C3N4 and PBA to generate interactive networks of g-C3N4 nanosheets-covered PBA nano-protuberances on NF surfaces, which further expended the electrode/electrolyte interfaces. Based on the merits from this unique hierarchical structure and the synergy effect of PBA and g-C3N4, the optimized g-C3N4/PBA/NF electrode exhibited a maximum areal capacitance of 3366 mF cm-2 at current of 2 mA cm-2, as well as 2118 mF cm-2 even under large current of 20 mA cm-2. The solid-state asymmetric supercapacitor using g-C3N4/PBA/NF electrode possessed an extended working potential window of 1.8 V, prominent energy density of 0.195 mWh cm-2 and power density of 27.06 mW cm-2. Compared to the device with pure NiFe-PBA electrode, a better cyclic stability with capacitance retention rate of 80% after 5000 cycles was also achieved due to the protective effect of g-C3N4 shells on the etching of PBA nano-protuberances in electrolyte. This work not only builds a promising electrode material for supercapacitors, but also provide an effective way to apply molten salt-synthesized g-C3N4 nanosheet without purification.

Carbon dots as light-responsive oxidase-like nanozyme for colorimetric detection of total antioxidant capacity in fruits.

Evaluation of total antioxidant capacity (TAC) in fruits is essential for dietary guidance and health monitoring. Here, we have exploited light-response carbon dots (CDs) as oxidase-like nanozyme to determine the TAC of fruits. The CDs possess excellent oxidase-like activity with light stimulation due to the accelerated intramolecular charge transfer caused by abundant electron donating/drawing groups in precursors. The scavenger experiment reveals that the catalytic intermediate could be hydroxyl radical, which can oxidize the colorimetric substrate. With the introduction of antioxidants, the oxidization of colorimetric substrate will be alleviated due to the scavenging of this intermediate by antioxidants. Based on this, we have successfully detected three antioxidants and obtained TAC of fruits with desirable results. This work affords a rapid, cost-effective and convenient analysis tool for TAC, as well as building a strong bridge between CDs and the development of photo-responsive oxidase-like nanozymes.

Damage-Free and Time-Saving Platform Integrated by a Flow Membrane Separation Device and a Dual-Target Biofuel Cell-Based Biosensor for Continuous Sorting and Detection of Exosomes and Host Cells in Human Serum.

The growth relationship between exosomes (EXOs) and the host cells is highly desired for tumor evaluations, which puts forward high demand on the accurate and convenient acquisition of their individual quantitative information. However, the tedious and destructive separation process and the requirement of dual-channel detection make it become an extremely challenging task. Herein, we integrated an enzymatic biofuel cell (EBFC)-powered biosensor with a flow cell-supported membrane separation device (FMSC) to develop a continuous separation and detection platform for EXOs and host cancer cells in human serum. The FMSC equipped with an aluminum oxide membrane served as a size-dependent sorting unit to nondestructively extract EXOs from human serum within 5 min, representing a 99.3% reduction in isolating time compared to ultracentrifugation. The EBFC-powered biosensors modified with different aptamers on anodes and cathodes were used as a dual-channel sensing unit. By regulating the controlling valves of different fluid passages, the extracted EXOs and residual host cells could be successively inputted into EBFC-powered biosensors, which generated a segmental degradation in output performance due to the EXO-and host cell-caused increase in the steric hindrance of anodes and cathodes, respectively. Based on these degradations, we obtained the quantitative information of EXOs and host cells with a record-breaking sensitivity (EXOs: 5.59 × 103 particles/mL and host cells: 25 cells/mL). Moreover, the growth relationship between EXOs and host cells was also built, which would be beneficial for the disclosure of the growth state or even more detailed biology information of tumor.

Three-dimensional carbon dots/Prussian blue analogues nanocubes /nickel foams as self-standing electrodes for high-performance hybrid electrochemical capacitors.

Developing the high-performance supercapacitors is overwhelmingly dependent on the composition design and structure tailoring of electrode materials. By a one-step solution method, the composite of carbon dots/Prussian blue analogues nanocubes-incorporated three-dimensional Ni foams was prepared and used as a self-standing positive electrode for hybrid electrochemical capacitors (HEC). Aside from the role of Ni source for Prussian blue analogues (PBA), Ni foams acts as 3D conductive supports, making electrolytes more accessible to the internal surface of electrode. Meanwhile, carbon dots can be absorbed for the formation of carbon dots/PBA nanocubes on Ni foams surfaces, offering optimized interfaces for the interactions between electrodes and electrolytes and relieving the decomposition of PBA in alkaline electrolyte. With these merits, the carbon dots/Prussian blue analogues nanocubes-Ni foams electrode in the hybrid electrolyte of 0.5 M KOH and 1.3 M Na2SO4 exhibits a maximum specific capacity of 659 C g-1 at current density of 0.5 A g-1 and 344 C g-1 even under large current density of 5 A g-1. An extended working potential window of 1.8 V, high energy density of 65 Wh kg-1 and high power density of 4.052 kW kg-1 as well as improved cyclic stability are also achieved in the assembled HEC. This study builds a boulevard to improve the application potential of PBA in HEC, which will be beneficial for the development of supercapacitors.

Label-Free Probing of Electron Transfer Kinetics of Single Microbial Cells on a Single-Layer Graphene via Structural Color Microscopy.

Studies of electron transfer at the population level veil the nature of the cell itself; however, in situ probing of the electron transfer dynamics of individual cells is still challenging. Here we propose label-free structural color microscopy for this aim. We demonstrate that Shewanella oneidensis MR-1 cells show unique structural color scattering, changing with the redox state of cytochrome complexes in the outer membrane. It enables quantitatively and noninvasive studies of electron transfer in single microbial cells during bioelectrochemical activities, such as extracellular electron transfer (EET) on a transparent single-layer graphene electrode. Increasing the applied potential leads to the associated EET current, accompanied by more oxidized cytochromes. The high spatiotemporal resolution of the proposed method not only demonstrates the large diversity in EET activity among microbial cells but also reveals the subcellular asymmetric distribution of active cytochromes in a single cell. We anticipate that it provides a potential platform for further exploring the electron transfer mechanism of subcellular structure.

Layer-by-layer assembly of Au and CdS nanoparticles on the surface of bacterial cells for photo-assisted bioanodes in microbial fuel cells.

Surface modification of exoelectrogens with photoelectric materials is a promising way for achieving photo-assisted microbial fuel cells (MFCs). However, the poor conductivity of most photoelectric materials inevitably hampers the electron transfer inside bacterial biofilms. Herein, by utilizing the electrostatic layer-by-layer assembly strategy, the conductive Au nanoparticles (NPs) and photo-responsive CdS NPs were alternatively modified onto the surface of Escherichia coli for photo-assisted bioanodes in MFCs. The CdS layer was found to protect the bacterial cells from light illumination-induced inactivation. When the CdS layer coexisted with an outer layer of Au NPs, the modification of the CdS layers can generate photocurrent without any loss of biocurrent, because the outer Au layer could serve as a conductive channel for the photoelectron and bioelectron transfer between each bacterium. But the increase of CdS layers failed to further improve the photocurrent, implying that the light was inaccessible to the inner CdS layer. This work brings a universal way to fabricate conductive and photo-responsive bacteria, which would deepen the application of cell-surface modification technology in photo-assisted MFCs.

Electrode Materials Engineering in Electrocatalytic CO2 Reduction: Energy Input and Conversion Efficiency.

Electrocatalytic CO2 reduction (ECR) is a promising technology to simultaneously alleviate CO2 -caused climate hazards and ever-increasing energy demands, as it can utilize CO2 in the atmosphere to provide the required feedstocks for industrial production and daily life. In recent years, substantial progress in ECR systems has been achieved by the exploitation of various novel electrode materials. The anodic materials and cathodic catalysts that have, respectively, led to high-efficiency energy input and effective heterogenous catalytic conversion in ECR systems are comprehensively reviewed. Based on the differences in the nature of energy sources and the role of materials used at the anode, the fundamentals of ECR systems, including photo-anode-assisted ECR systems and bio-anode-assisted ECR systems, are explained in detail. Additionally, the cathodic reaction mechanisms and pathways of ECR are described along with a discussion of different design strategies for cathode catalysts to enhance conversion efficiency and selectivity. The emerging challenges and some perspective on both anode materials and cathodic catalysts are also outlined for better development of ECR systems.

Plasmon Coupling-Enhanced Raman Sensing Platform Integrated with Exonuclease-Assisted Target Recycling Amplification for Ultrasensitive and Selective Detection of microRNA-21.

A "signal-off" surface-enhanced Raman scattering (SERS) platform has been constructed for ultrasensitive detection of miRNA-21 by integrating exonuclease-assisted target recycling amplification with a plasmon coupling enhancement effect. On this platform, Raman-labeled Au nanostar (AuNS) probes can be covalently linked with the thiolated aptamer (Apt) on the Au-decorated silicon nanowire arrays (SiNWAs/Au) substrate, creating a coupled electromagnetic field between the substrate and the probes to enhance Raman signal. In the presence of miRNA-21, T7 exonuclease specifically hydrolyzed Apt on Apt/miRNA duplex to release miRNA-21. The regenerated element could then initiate another cycle of Apt/miRNA duplex formation and Apt cleavage. Correspondingly, the capture ability of substrate toward probes and the plasmon coupling effect between them were both diminished, giving a prominent attenuation of Raman intensity that can work as the detection signal. Due to the cascading integration between the target cycle process and the plasmon coupling effect, the present platform displayed a very low detection limit (0.34 fM, 3σ) for miRNA-21 detection. Furthermore, it was proven to be effective for analyzing miRNA-21 in biological samples and distinguishing the expression levels of miRNA-21 in MCF-7 cells and NIH3T3 cells, which became a promising tool to monitor miRNA-21 in cancer auxiliary diagnosis and drug screening.

Mediation of Extracellular Polymeric Substances in Microbial Reduction of Hematite by Shewanella oneidensis MR-1.

Extracellular electron transfer (EET) plays a fundamental role in microbial reduction/oxidation of minerals. Extracellular polymeric substances (EPS) surrounding the cells constitute a matrix that separates the cell's outer membrane from insoluble minerals and environmental fluid. This study investigated the effects of EPS on EET processes during microbial reduction of hematite by the iron-reducing strain Shewanella oneidensis MR-1 (MR-1). Electrochemical characterization techniques were employed to determine the influence of EPS components on the redox ability of MR-1. Cells with removed EPS exhibited approximately 30% higher hematite reduction than regular MR-1 cells, and produced a current density of 56 µA cm-2, corresponding to 3-4 fold that of regular MR-1. The superior EET of EPS-deprived cells could be attributed to direct contact between outer membrane proteins and hematite surface, as indicated by more redox peaks being detected by cyclic voltammetry and differential pulse voltammetry. The significantly reduced current density of MR-1 cells treated with proteinase K and deoxyribonuclease suggests that the electron transfer capacity across the EPS layer depends mainly on the spatial distribution of specific proteins and electron shuttles. Exopolysaccharides in EPS tend to inhibit electron transfer, however they also favor the attachment of cells onto hematite surfaces. Consistently, the charge transfer resistance of cells lacking EPS was only 116.3 Ω, approximately 44 times lower than that of regular cells (5,139.1 Ω). These findings point to a negative influence of EPS on EET processes for microbial reduction/oxidation of minerals.

Harvesting energy from cellulose through Geobacter sulfurreducens in Unique ternary culture.

In this study, both electricity generation capability and biodegradation process of carboxymethyl cellulose (CMC) were investigated using a defined ternary culture of Paenibacillus sp., Klebsiella sp. and Geobacter sulfurreducens as biocatalysts in MFCs. The maximum current density achieved by the ternary culture from CMC was 621 ±â€¯23 µA cm-2 in half-cell experiments and the maximum power density reached to 1146 ±â€¯28 mW m-2 in two-chamber MFCs. Meanwhile, the ternary culture also possessed three times higher CMC degradation capability compared to the pure strain J1. Besides, the key metabolite products, including cellobiose, glucose, acetate, were quantified by high performance liquid chromatography (HPLC) to illustrate the biodegradation process of CMC. The high electricity generation performance mainly resulted from the "division-of-labor" based cooperation and the enhanced extracellular electron transfer caused by the electron shuttle secreted by Klebsiella sp. This study highlighted the synergistic effect of specific community on electricity generation using CMC as carbon source, and laid the foundation for further optimization of more efficient and stable microbial consortia for bioenergy applications.

A glucose/O2 fuel cell-based self-powered biosensor for probing a drug delivery model with self-diagnosis and self-evaluation.

Extending the application of self-powered biosensors (SPB) into the drug delivery field is highly desirable. Herein, a robust glucose/O2 fuel cell-based biosensor is successfully integrated with a targeted drug delivery system to create a self-sustained and highly compact drug delivery model with self-diagnosis and self-evaluation (DDM-SDSE). The glucose/O2 fuel cell-based biosensor firstly performs its diagnostic function by detecting the biomarkers of cancer. The drug delivery system attached on the anode of the glucose/O2 fuel cell can be released during the diagnostic operation to guarantee the occurrence of a therapy process. Accompanied by the therapy process, the glucose/O2 fuel cell-based biosensor can also act as an evaluation component to dynamically monitor the therapy efficacy by analyzing drug-induced apoptotic cells. In addition, the use of an abiotic catalyst largely improves the stability of the glucose/O2 fuel cell without sacrificing the output performance, further ensuring long-time dynamic evaluation as well as highly sensitive diagnosis and evaluation in this DDM-SDSE. Therefore, the present study not only expands the application of SPBs but also offers a promising in vitro "diagnosis-therapy-evaluation" platform to acquire valuable information for clinical cancer therapy.

Plasmonic Au nanostar Raman probes coupling with highly ordered TiO2/Au nanotube arrays as the reliable SERS sensing platform for chronic myeloid leukemia drug evaluation.

The accurate therapeutic evaluation for chronic myeloid leukemia (CML) drug is of great importance to minimize side effects and enhance efficacy. Herein, a facile and precise surface-enhanced scattering (SERS) approach based on coupled plasmonic field has been introduced to evaluate the therapeutic outcomes of antileukemia drug through ultrasensitive assay of caspase-3 activity in apoptotic cells. Caspase-3 as an apoptosis indicator could specifically cleave the N-terminus of biotinylated DEVD-peptide (biotin-Gly-Asp-Gly-Asp-Glu-Val-Asp-Gly-Cys) immobilized on the Au nanoparticle-decorated TiO2 nanotube arrays (TiO2/Au NTAs) substrate. After the enzyme cleavage with caspase-3, Raman-labelled Au nanostar (AuNS) probes captured the residual DEVD-peptides via the recognition between streptavidin and biotin, thus resulting in an enhanced Raman response on the SERS platform. The variation of Raman intensity revealed caspase-3 activity that reflected the chemotherapeutic effect. On this platform, AuNS nanoprobes offered a large number of binding sites and intrinsic "hot spots" for Raman reporters, while TiO2/Au NTAs rendered a homogenously coupled electromagnetic field between the adjacent repeated units over the large area. In particular, a spatially expanding plasmonic field formed by coupling AuNSs with TiO2/Au NTAs would further heighten Raman enhancement. Taking these advantages, the strong and uniform Raman signals were achieved. Furthermore, the practicability investigation witnessed that the proposed SERS strategy was available to evaluate the therapeutic effect of dasatinib on CML K562 cells. The developed method possesses fascinating advantages of cost-effectiveness, excellent reproducibility and high sensitivity, which endows it with promising potential in apoptosis monitoring and anticancer drug development.

Oxygen Species on Nitrogen-Doped Carbon Nanosheets as Efficient Active Sites for Multiple Electrocatalysis.

Designing and synthesizing nanomaterials with high coverages of active sites is one of the most-pivotal factors in the construction of state-of-the-art electrocatalysts with high performance. Herein, we proposed a facile in situ templated method for the fabrication of oxygen-species-modified nitrogen-doped carbon nanosheets (O-N-CNs). The epoxy oxygen and ketene oxygen combined with graphitic-nitrogen defects in O-N-CNs gave more active sites for the oxygen-reduction reaction (ORR) and the oxygen-evolution reaction (OER), as proven via theoretical and experimental results, while the carbonyl-oxygen and epoxy-oxygen species showed more efficient electrocatalytic activity for the hydrogen evolution reaction (HER). Hence, the O-N-CNs showed highly active electrocatalytic performance toward ORR, OER, and HER. More importantly, the superior multifunctional electrocatalytic activity of O-N-CNs allowed their use in the construction of Zn-air batteries to power the corresponding water-splitting cells. This work can offer an understanding of underlying mechanisms of oxygen species on N-doped carbon materials toward multiple electrocatalysis and facilitate the engineering of electrocatalysts for energy-storage and -conversion devices.

Correction: Visible-light-enhanced power generation in microbial fuel cells coupling with 3D nitrogen-doped graphene.

Correction for 'Visible-light-enhanced power generation in microbial fuel cells coupling with 3D nitrogen-doped graphene' by Dan Guo et al., Chem. Commun., 2017, DOI: .

Visible-light-enhanced power generation in microbial fuel cells coupling with 3D nitrogen-doped graphene.

A new visible-light-assisted microbial fuel cell composed of a three-dimensional nitrogen-doped graphene self-standing sponge anode and a photoresponsive cathode has been developed for achieving multiple energy conversion and a higher power output.

Living and Conducting: Coating Individual Bacterial Cells with In†Situ Formed Polypyrrole.

Coating individual bacterial cells with conjugated polymers to endow them with more functionalities is highly desirable. Here, we developed an in situ polymerization method to coat polypyrrole on the surface of individual Shewanella oneidensis MR-1, Escherichia coli, Ochrobacterium anthropic or Streptococcus thermophilus. All of these as-coated cells from different bacterial species displayed enhanced conductivities without affecting viability, suggesting the generality of our coating method. Because of their excellent conductivity, we employed polypyrrole-coated Shewanella oneidensis MR-1 as an anode in microbial fuel cells (MFCs) and found that not only direct contact-based extracellular electron transfer is dramatically enhanced, but also the viability of bacterial cells in MFCs is improved. Our results indicate that coating individual bacteria with conjugated polymers could be a promising strategy to enhance their performance or enrich them with more functionalities.

Nanostructured material-based biofuel cells: recent advances and future prospects.

During the past decade, biofuel cells (BFCs) have emerged as an emerging technology on account of their ability to directly generate electricity from biologically renewable catalysts and fuels. Due to the boost in nanotechnology, significant advances have been accomplished in BFCs. Although it is still challenging to promote the performance of BFCs, adopting nanostructured materials for BFC construction has been extensively proposed as an effective and promising strategy to achieve high energy production. In this review, we presented the major novel nanostructured materials applied for BFCs and highlighted the breakthroughs in this field. Based on different natures of the bio-catalysts and electron transfer process at the bio-electrode surfaces, the fundamentals of BFC systems, including enzymatic biofuel cells (EBFCs) and microbial fuel cells (MFCs), have been elucidated. In particular, the principle of electrode materials design has been detailed in terms of enhancing electrical communications between biological catalysts and electrodes. Furthermore, we have provided the applications of BFCs and potential challenges of this technology.

Graphene/Fe3 O4 Nanocomposites as Efficient Anodes to Boost the Lifetime and Current Output of Microbial Fuel Cells.

The enhancement of microbial activity and electrocatalysis through the design of new anode materials is essential to develop microbial fuel cells (MFCs) with longer lifetimes and higher output. In this research, a novel anode material, graphene/Fe3 O4 (G/Fe3 O4 ) composite, has been designed for Shewanella-inoculated MFCs. Because the Shewanella species could bind to Fe3 O4 with high affinity and their growth could be supported by Fe3 O4 , the bacterial cells attached quickly onto the anode surface and their long-term activity improved. As a result, MFCs with reduced startup time and improved stability were obtained. Additionally, the introduction of graphene not only provided a large surface area for bacterial attachment, but also offered high electrical conductivity to facilitate extracellular electron transfer (EET). The results showed that the current and power densities of a G/Fe3 O4 anode were much higher than those of each individual component as an anode.

Bacteria-Affinity 3D Macroporous Graphene/MWCNTs/Fe3O4 Foams for High-Performance Microbial Fuel Cells.

Promoting the performance of microbial fuel cells (MFCs) relies heavily on the structure design and composition tailoring of electrode materials. In this work, three-dimensional (3D) macroporous graphene foams incorporated with intercalated spacer of multiwalled carbon nanotubes (MWCNTs) and bacterial anchor of Fe3O4 nanospheres (named as G/MWCNTs/Fe3O4 foams) were first synthesized and used as anodes for Shewanella-inoculated microbial fuel cells (MFCs). Thanks to the macroporous structure of 3D graphene foams, the expanded electrode surface by MWCNTs spacing, as well as the high affinity of Fe3O4 nanospheres toward Shewanella oneidensis MR-1, the anode exhibited high bacterial loading capability. In addition to spacing graphene nanosheets for accommodating bacterial cells, MWCNTs paved a smoother way for electron transport in the electrode substrate of MFCs. Meanwhile, the embedded bioaffinity Fe3O4 nanospheres capable of preserving the bacterial metabolic activity provided guarantee for the long-term durability of the MFCs. With these merits, the constructed MFC possessed significantly higher power output and stronger stability than that with conventional graphite rod anode.