Comparative analysis of microbial fuel cell based biosensors developed with a mixed culture and Shewanella loihica PV-4 and underlying biological mechanism

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.

Artificial and Biosynthetic Nanoparticles Boost Bioelectrochemical Reactions via Efficient Bidirectional Electron Transfer of Shewanella loihica

Bioelectrochemical reactions using whole-cell biocatalysts are promising carbon-neutral approaches because of their easy operation, low cost, and sustainability. Bidirectional (outward or inward) electron transfer via exoelectrogens plays the main role in driving bioelectrochemical reactions. However, the low electron transfer efficiency seriously inhibits bioelectrochemical reaction kinetics. Here, a three dimensional and artificial nanoparticles-constituent inverse opal-indium tin oxide (IO-ITO) electrode is fabricated and employed to connect with exoelectrogens (Shewanella loihica PV-4). The above electrode collected 128-fold higher cell density and exhibited a maximum current output approaching 1.5 mA cm-2 within 24 h at anode mode. By changing the IO-ITO electrode to cathode mode, the exoelectrogens exhibited the attractive ability of extracellular electron uptake to reduce fumarate and 16 times higher reverse current than the commercial carbon electrode. Notably, Fe-containing oxide nanoparticles are biologically synthesized at both sides of the outer cell membrane and probably contributed to direct electron transfer with the transmembrane c-type cytochromes. Owing to the efficient electron exchange via artificial and biosynthetic nanoparticles, bioelectrochemical CO2 reduction is also realized at the cathode. This work not only explored the possibility of augmenting bidirectional electron transfer but also provided a new strategy to boost bioelectrochemical reactions by introducing biohybrid nanoparticles.

Effects of simulated microgravity on current generation of electrochemically active bacteria: Insights from case-control study using random positioning machine

Electrochemically active bacteria (EAB) exhibit promising prospects for space exploration and life support systems. However, the effects of the space environment on EAB are unclear. In this study, the effects of simulated microgravity on the current generation of mixed-culture EAB were illustrated, and the underlying mechanism was elucidated. The results demonstrated that the electrochemical activity of mixed-culture EAB was enhanced, which was mainly due to the enrichment of Geobacter and the increase in EAB biomass. Additionally, the genes and proteins of the biofilm changed obviously under simulated microgravity conditions, including: I) genes related to signal transfer, II) genes related to cell wall synthesis, and III) genes related to riboflavin synthesis. This study first revealed the enrichment in EAB abundance, the increase in EAB biomass, and the promotion of current generation under simulated microgravity.

Recent progress in the characterization and application of exo-electrogenic microorganisms

Exo-electrogenic microorganisms are characterized by their special metabolic capability of transferring metabolic electrons out of their cell, into insoluble external electron acceptors such as iron or manganese oxides and electrodes, or vice versa take up electron from electrodes. Their conventional application is primarily limited to microbial fuel cells for electrical power generation and microbial electrolysis cells for the production of value-added products such as biohydrogen, biomethane and hydrogen peroxide. The utility of exo-electrogenic organisms has expanded into many other applications in recent times. Such examples include microbial desalination cells, microbial electro-synthesis cells producing value-added chemicals such as bio-butanol and their applications in other carbon sequestration technologies. Additionally, electrochemically-active organisms are now beginning to be employed in biosensor applications for environmental monitoring. Additionally, the utility of biocathodes in bio-electrochemical systems is also a novel application in catalyzing the cathodic oxygen reduction reaction to enhance their electrochemical performance. Advances have also been made in the expansion and use of other organisms such as the usage of photosynthetic microorganisms for the fabrication of self-sustained bio-electrochemical systems. This review attempts to provide a comprehensive picture of the state-of the art of exo-electrogenic organisms and their novel utility in bioelectrochemical systems.

Instant water toxicity detection based on magnetically-constructed electrochemically active biofilm

Water toxicity determination with electrochemically active bacteria (EAB) is promising in the early warning of water pollution. However, limited by tedious biofilm formation, natural EAB biofilms are uncapable of the instant detection of water toxicity, resulting in the failure for the emergency monitoring of water pollution. To solve this problem, a novel method for the rapid construction of EAB biofilms using magnetic adsorption was established, and the performance of instant water toxicity detection with magnetically-constructed EAB biofilm was investigated. The results demonstrate that EAB biofilms were magnetically constructed in less than 30 min, and magnetically-constructed EAB biofilm generated stable currents even under continuous flow conditions. Magnetically-constructed EAB biofilms realized instant water toxicity detection, and the sensitivity increased with the decrease of magnetic field intensity. Low magnetic field intensity resulted in a loose biofilm structure, which is conducive to toxic pollutant penetration. The detection limit for Cu2+, phenol, and Cd2+ achieved 0.07 mg/L with optimal magnetic field intensity, and the detection time was less than 30 min. This study broadens the application of water toxicity determination with EAB, and establishes a foundation for the instant and continuous detection of water toxicity with EAB.

Mechanism and applications of bidirectional extracellular electron transfer of Shewanella

Electrochemically active microorganisms (EAMs) play an important role in the fields of environment and energy. Shewanella is the most common EAM. Research into Shewanella contributes to a deeper comprehension of EAMs and expands practical applications. In this review, the outward and inward extracellular electron transfer (EET) mechanisms of Shewanella are summarized and the roles of riboflavin in outward and inward EET are compared. Then, four methods for the enhancement of EET performance are discussed, focusing on riboflavin, intracellular reducing force, biofilm formation and substrate spectrum, respectively. Finally, the applications of Shewanella in the environment are classified, and the restrictions are discussed. Potential solutions and promising prospects for Shewanella are also provided.

A Weak Electricigen-Based Bioelectrochemical Sensor for Real-Time Monitoring of Chemical Pollutants in Water

Electroactive microorganisms are now understood to be abundant across nature, though many are categorized as "weak electricigens" not suitable for reasonable power generation. We report the use of weak electricigens from the natural environment for rapid, real-time water quality monitoring. Using a variety of pesticides as model chemical pollutants, the bioelectrochemical sensor was responsive within minutes at all concentrations tested (0.05-2 ppm) and could be repreatedly used long-term. Due to the prevalence of electroactive microorganisms in the natural environment, such sensors could work in tandem with conventional monitoring methods and may be useful for detecting emerging contaminants.

Microbial Fuel Cell-Based Organic Matter Sensors: Principles, Structures and Applications

Wastewater contains a significant quantity of organic matter, continuously causing environmental pollution. Timely and accurate detection of organic content in water can facilitate improved wastewater treatment and better protect the environment. Microbial fuel cells (MFCs) are increasingly recognized as valuable biological monitoring systems, due to their ability to swiftly detect organic indicators such as biological oxygen demand (BOD) and chemical oxygen demand (COD) in water quality. Different types of MFC sensors are used for BOD and COD detection, each with unique features and benefits. This review focuses on different types of MFC sensors used for BOD and COD detection, discussing their benefits and structural optimization, as well as the influencing factors of MFC-based biomonitoring systems. Additionally, the challenges and prospects associated with the development of reliable MFC sensing systems are discussed.

The versatility of microbial fuel cells as tools for organic matter monitoring

Water monitoring and remediation require robust, low-cost, and reliable test systems that can couple with prompt treatment interventions. Organic matter (BOD, COD), toxicants, heavy metals, and other pollutants in water need to be regularly inspected. Microbial fuel cells (MFCs) have already gained popularity as BOD biomonitoring systems as these don't need an external transducer or power source. Moreover, these systems are cost-effective, compact, biodegradable, reusable, portable, and applicable for on-site measurements. MFCs truly stands out as online BOD measurement devices as they provide wide detection range (0-25 g/L), low response time (2-4 min) and longer stability in continuous operations (2-5 years) in a cost-effective approach. This review examines the benefits, kinds, performance metrics, and signal optimization of the current state-of-the-art of the BOD measurement, with detailed focus on MFC-based BOD biomonitoring systems. This review covers the important technological breakthroughs in practical applications with associated bottlenecks to develop reliable sensing systems.

Microbial Biosensors for Rapid Determination of Biochemical Oxygen Demand: Approaches, Tendencies and Development Prospects

One of the main indices of the quality of water is the biochemical oxygen demand (BOD). A little over 40 years have passed since the practical application of the first microbial sensor for the determination of BOD, presented by the Japanese professor Isao Karube. This time span has brought new knowledge to and practical developments in the use of a wide range of microbial cells based on BOD biosensors. At present, this field of biotechnology is becoming an independent discipline. The traditional BOD analysis (BOD₅) has not changed over many years; it takes no less than 5 days to carry out. Microbial biosensors can be used as an alternative technique for assessing the BOD attract attention because they can reduce hundredfold the time required to measure it. The review examines the experience of the creation and practical application of BOD biosensors accumulated by the international community. Special attention is paid to the use of multiple cell immobilization methods, signal registration techniques, mediators and cell consortia contained in the bioreceptor. We consider the use of nanomaterials in the modification of analytical devices developed for BOD evaluation and discuss the prospects of developing new practically important biosensor models.

Microbial fuel cells for bioelectricity production from waste as sustainable prospect of future energy sector

Microbial fuel cell (MFC) is lauded for its potentials to solve both energy crisis and environmental pollution. Technologically, it offers the capability to harness electricity from the chemical energy stored in the organic substrate with no intermediate steps, thereby minimizes the entropic loss due to the inter-conversion of energy. The sciences underneath such MFCs include the electron and proton generation from the metabolic decomposition of the substrate by microbes at the anode, followed by the shuttling of these charges to cathode for electricity generation. While its promising prospects were mutually evinced in the past investigations, the upscaling of MFC in sustaining global energy demands and waste treatments is yet to be put into practice. In this context, the current review summarizes the important knowledge and applications of MFCs, concurrently identifies the technological bottlenecks that restricted its vast implementation. In addition, economic analysis was also performed to provide multiangle perspectives to readers. Succinctly, MFCs are mainly hindered by the slow metabolic kinetics, sluggish transfer of charged particles, and low economic competitiveness when compared to conventional technologies. From these hindering factors, insightful strategies for improved practicality of MFCs were formulated, with potential future research direction being identified too. With proper planning, we are delighted to see the industrialization of MFCs in the near future, which would benefit the entire human race with cleaner energy and the environment.

Microbial Electrochemical Systems: Principles, Construction and Biosensing Applications

Microbial electrochemical systems are a fast emerging technology that use microorganisms to harvest the chemical energy from bioorganic materials to produce electrical power. Due to their flexibility and the wide variety of materials that can be used as a source, these devices show promise for applications in many fields including energy, environment and sensing. Microbial electrochemical systems rely on the integration of microbial cells, bioelectrochemistry, material science and electrochemical technologies to achieve effective conversion of the chemical energy stored in organic materials into electrical power. Therefore, the interaction between microorganisms and electrodes and their operation at physiological important potentials are critical for their development. This article provides an overview of the principles and applications of microbial electrochemical systems, their development status and potential for implementation in the biosensing field. It also provides a discussion of the recent developments in the selection of electrode materials to improve electron transfer using nanomaterials along with challenges for achieving practical implementation, and examples of applications in the biosensing field.

Dual detection of biochemical oxygen demand and nitrate in water based on bidirectional Shewanella loihica electron transfer

This study for the first time proposed a method for simultaneously measuring BOD and nitrate in water using electrochemically active bacteria. Firstly, the bidirectional extracellular electron transfer (EET) capability of a model electricigen Shewanella loihica PV-4 was revealed. Then, based on the respective outward and inward EET, S. loihica PV-4 was utilized to detection BOD and nitrate. The results demonstrated a positive correlation between the outward EET and BOD (from 0 mg/L to 435 mg/L) while a negative correlation between the inward EET and nitrate (from 0 mg/L to 7 mg/L); both the relationships were well fitted by the combination of traditional linear model and Michaelis-Menten model (R²>0.96). Finally, a dual detection method for BOD and nitrate measurements was established based on the ano-cathodophilic capability of S. loihica PV-4 biofilm, and exhibited the characteristics of high accuracy (>80%) and fast analysis (<1h), suggesting a promising prospect in water monitoring.

Bifunctional cathode using a biofilm and Pt/C catalyst for simultaneous electricity generation and nitrification in microbial fuel cells

Biofouling frequently causes catalyst deterioration at the cathode of microbial fuel cells (MFCs). A biofilm-covered Pt/C cathode (BPC) was fabricated via in situ cultivation of a biofilm on a Pt/C cathode (PC) in a dual-chambered MFC, which enables effective removal of NH4+-N and copious generation of electricity. Experimental results show 99% NH4+-N removal by the nitrifying bacteria that constitute 35.7% of all microorganisms on the BPC and a maximum BPC-MFC power density of 0.97 W/m2, which is comparable to that of PC-MFCs (0.99 W/m2). BPC biofilm size is restricted by the limited amount of organic material in the cathode chamber, which constrains the biomass to less than 0.3 g protein /m2. The bifunctional-cathode equipped MFC shows great promise as an energy-saving technology for wastewater treatment in the future.

A novel biosensor for zinc detection based on microbial fuel cell system

Microbial fuel cell (MFC) biosensors are self-sustainable device for monitoring of various substrates; however, for heavy metals detection are still scarce. In this study, E. coli BL21 was engineered to express the zntR, ribB, and oprF genes with P_zntA promoter, which could sense zinc (Zn²⁺) for riboflavin and porin production. The engineered strain produced high levels of riboflavin (2.4-3.6 μM) and improved cell membrane permeability, with a positive correlation of Zn²⁺ (0-400 μM). The strain was then employed in MFC biosensor under the following operational parameters: external resistance 1000 Ω, pH 9, and temperature 37 °C for Zn²⁺ sensing. The maximum voltages (160, 183, 260, 292, and 342 mV) of the constructed MFC biosensor have a linear relationship with Zn²⁺ concentrations (0, 100, 200, 300, and 400 μM, respectively) (R² = 0.9777). An Android App was developed for the biosensor system that could sense Zn²⁺ in real-time and in situ. The biosensor was applied to wastewater with different Zn²⁺ concentrations and the results showed that the detection range for Zn²⁺ was 20-100 μM, which covers common Zn²⁺ safety standards. The results obtained with developed MFC biosensor were comparable to conventional methods such as colorimetric, flame atomic absorption spectroscopy (FAAS), and inductively coupled plasma optical emission spectroscopy (ICP-OES). In summary, MFC biosensor with biosynthetic strain is an efficient and affordable system for real-time monitoring and sensing of heavy metals.

Cell-based biosensors: Recent trends, challenges and future perspectives

Existing at the interface of biology and electronics, living cells have been in use as biorecognition elements (bioreceptors) in biosensors since the early 1970s. They are an interesting choice of bioreceptors as they allow flexibility in determining the sensing strategy, are cheaper than purified enzymes and antibodies and make the fabrication relatively simple and cost-effective. And with advances in the field of synthetic biology, microfluidics and lithography, many exciting developments have been made in the design of cell-based biosensors in the last about five years. 3D cell culture systems integrated with electrodes are now providing new insights into disease pathogenesis and physiology, while cardiomyocyte-integrated microelectrode array (MEA) technology is set to be standardized for the assessment of drug-induced cardiac toxicity. From cell microarrays for high-throughput applications to plasmonic devices for anti-microbial susceptibility testing and advent of microbial fuel cell biosensors, cell-based biosensors have evolved from being mere tools for detection of specific analytes to multi-parametric devices for real time monitoring and assessment. However, despite these advancements, challenges such as regeneration and storage life, heterogeneity in cell populations, high interference and high costs due to accessory instrumentation need to be addressed before the full potential of cell-based biosensors can be realized at a larger scale. This review summarizes results of the studies that have been conducted in the last five years toward the fabrication of cell-based biosensors for different applications with a comprehensive discussion on the challenges, future trends, and potential inputs needed for improving them.

On-going applications of Shewanella species in microbial electrochemical system for bioenergy, bioremediation and biosensing

Microbial electrochemical system (MES) has attracted ever-growing interest as a promising platform for renewable energy conversion and bioelectrochemical remediation. Shewanella species, the dissimilatory metal reduction model bacteria with versatile extracellular electron transfer (EET) strategies, are the well-received microorganisms in diverse MES devices for various practical applications as well as microbial EET mechanism investigation. Meanwhile, the available genomic information and the unceasing established gene-editing toolbox offer an unprecedented opportunity to boost the applications of Shewanella species in MES. This review thoroughly summarizes the status quo of the applications of Shewanella species in microbial fuel cells for bioelectricity generation, microbial electrosynthesis for biotransformation of valuable chemicals and bioremediation of environment-hazardous pollutants with synoptical discussion on their EET mechanism. Recent advances in rational design and genetic engineering of Shewanella strains for either promoting the MES performance or broadening their applications are surveyed. Moreover, some emerging applications beyond electricity generation, such as biosensing and biocomputing, are also documented. The challenges and perspectives for Shewanella-based MES are also discussed elaborately for the sake of not only discovering new scientific lights on microbial extracellular respiratory but also propelling practical applications.