[object Object], [object Object], [object Object] et al.

Energy, Ecology and Environment • 2019

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Microbial Biotechnology • 2022

Abstract Protein nanowires are critical electroactive components for electron transfer of Geobacter sulfurreducens biofilm. To determine the applicability of the nanowire proteins in improving bioelectricity production, their genes including pilA , omcZ , omcS and omcT were overexpressed in G. sulfurreducens . The voltage outputs of the constructed strains were higher than that of the control strain with the empty vector (0.470–0.578 vs. 0.355 V) in microbial fuel cells (MFCs). As a result, the power density of the constructed strains (i.e. 1.39–1.58 W m −2 ) also increased by 2.62‐ to 2.97‐fold as compared to that of the control strain. Overexpression of nanowire proteins also improved biofilm formation on electrodes with increased protein amount and thickness of biofilms. The normalized power outputs of the constructed strains were 0.18–0.20 W g −1 that increased by 74% to 93% from that of the control strain. Bioelectrochemical analyses further revealed that the biofilms and MFCs with the constructed strains had stronger electroactivity and smaller internal resistance, respectively. Collectively, these results demonstrate for the first time that overexpression of nanowire proteins increases the biomass and electroactivity of anode‐attached microbial biofilms. Moreover, this study provides a new way for enhancing the electrical outputs of MFCs.

[object Object], [object Object], [object Object] et al.

Nanoscale • 2016

We report a miniaturized microbial fuel cell, integrated with a 3D free-standing graphene scaffold, delivering a record high power density of 11 220 W m −3 .

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Journal of The Electrochemical Society • 2022

While gold is a stable metal in water, it is not uncommon for microfluidic experimenters using biologically-relevant fluids such as phosphate-buffered saline (PBS) to witness their precious gold electrodes quickly vanish from the microchannel once the voltage exceeds a few volts. This stability issue concerns multiple fields where high voltage provides superior actuator or sensor performance, such as resistive pulse sensing (RPS), electroosmosis, electrowetting and so on. One solution to protect metallic electrodes is using alternative voltages (AV) as opposed to continuous voltages. After recalling that gold dissolution is enabled by the chloride ions present in most biologically-relevant solutions, we explore the stability conditions of the electrodes for voltages from 1 to 20 V pp (Peak to Peak voltage amplitude), actuation frequencies between 0 and 5 kHz, and for various pH and electrolytes (NaCl, Na 2 SO 4 , HCl). We find that the dissolution threshold voltage depends on the ratio of reaction to diffusion rate given by the Damkhöler number Da. In mass-transfer limited regime, the dissolution threshold is independent of the frequency, whereas the dissolution voltage is observed to grow as Da −1/2 in the reaction limited regime. These findings provide guidelines to design more reliable electrowetting, electroosmosis, dielectrophoresis and resistive pulse sensing devices.

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Energy Reports • 2023

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Analytical Methods • 2018

Introduction of bacterial inoculant into a chemostat bioreactor can lead to unwanted contamination of upstream elements via chemotaxis. Passive microfluidic elements show the potential to solve this problem.

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Annual Review of Analytical Chemistry • 2023

Biofilms are multicellular communities held together by a self-produced extracellular matrix and exhibit a set of properties that distinguish them from free-living bacteria. Biofilms are exposed to a variety of mechanical and chemical cues resulting from fluid motion and mass transport. Microfluidics provides the precise control of hydrodynamic and physicochemical microenvironments to study biofilms in general. In this review, we summarize the recent progress made in microfluidics-based biofilm research, including understanding the mechanism of bacterial adhesion and biofilm development, assessment of antifouling and antimicrobial properties, development of advanced in vitro infection models, and advancement in methods to characterize biofilms. Finally, we provide a perspective on the future direction of microfluidics-assisted biofilm research.

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International Journal of Hydrogen Energy • 2021

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Bioresource Technology • 2013

The efficiency of microbial fuel cells (MFCs) is affected by several factors such as activation overpotentials, ohmic losses and concentration polarization. These factors are handled in micro-sized MFCs using special electrodes with physically or chemically modified surfaces constructed with specified materials. Most of the existing μLscale MFCs show great potential in rapid screening of electrochemically-active microbes and electrode performance; although they generate significantly lower volumetric power density compared with their mL counterparts because of their high internal resistance. This review presents the development of microfluidic MFCs, with summarization of their advantages and challenges, and focuses on the efforts done to minimize the adverse effects of internal resistance (ohmic and non-ohmic) on their performance.

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npj Biofilms and Microbiomes • 2017

Abstract Bacteria often adhere to surfaces, where they form communities known as biofilms. Recently, it has been shown that biofilm formation initiates with the microscopically heterogeneous deposition of a skeleton of extracellular polymeric substances (EPS) by individual cells crawling on the surface, followed by growth of the biofilm into a surface-covering continuum. Here we report microfluidic experiments with Pseudomonas aeruginosa biofilms showing that their “hidden” heterogeneity can affect the later dynamics of their disruption. Using controlled air bubbles as a model for mechanical insult, we demonstrate that biofilm disruption is strongly dependent on biofilm age, and that disruption to early-stage biofilms can take the shape of a semi-regular pattern of ~15 µm diameter holes from which bacteria have been removed. We explain hole formation in terms of the rupture and retreat of the thin liquid layer created by the long bubble, which scrapes bacteria off the surface and rearranges their distribution. We find that the resulting pattern correlates with the spatial distribution of EPS: holes form where there is less EPS, whereas regions with more EPS act as strongholds against the scraping liquid front. These results show that heterogeneity in the microscale EPS skeleton of biofilms has profound consequences for later dynamics, including disruption. Because few attached cells suffice to regrow a biofilm, these results point to the importance of considering microscale heterogeneity when designing and assessing the effectiveness of biofilm removal strategies by mechanical forces.

[object Object], [object Object], [object Object] et al.

Biomicrofluidics • 2022

Bubbles in microfluidics—even those that appear to be negligibly small—are pervasive and responsible for the failure of many biological and chemical experiments. For instance, they block current conduction, damage cell membranes, and interfere with detection results. To overcome this unavoidable and intractable problem, researchers have developed various methods for capturing and removing bubbles from microfluidics. Such methods are multifarious and their working principles are very different from each other. In this review, bubble-removing methods are divided into two broad categories: active debubblers (that require external auxiliary equipment) and passive debubblers (driven by natural processes). In each category, three main types of methods are discussed along with their advantages and disadvantages. Among the active debubblers, those assisted by lasers, acoustic generators, and negative pressure pumps are discussed. Among the passive debubblers, those driven by buoyancy, the characteristics of gas–liquid interfaces, and the hydrophilic and hydrophobic properties of materials are discussed. Finally, the challenges and prospects of the bubble-removal technologies are reviewed to refer researchers to microfluidics and inspire further investigations in this field.

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Biomicrofluidics • 2017

Specially designed microfluidic bioflow cells were used to temporarily trap microbubbles during different inoculation stages of Pseudomonas sp. biofilms. Despite being eliminated many hours before biofilm appearance, templated growth could occur at former bubble positions. Bubble-templated growth was either continuous or in ring patterns, depending on the stage of inoculation when the bubbles were introduced. Templated biofilms were strongly enhanced in terms of their growth kinetics and structural homogeneity. High resolution confocal imaging showed two separate bubble-induced bacterial trapping modes, which were responsible for the altered biofilm development. It is concluded that static bubbles can be exploited for fundamental improvements to bioreactor performance, as well as open new avenues to study isolated bacteria and small colonies.

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Analytical Chemistry • 2018

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Bioelectrochemistry • 2011

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Lab Chip • 2006

We review transport characteristics of pressure-driven, multiphase flows through microchannel networks tens of nanometres to several hundred of micrometres wide with emphasis on conditions resulting in enhanced mixing and reduced axial dispersion. Dimensionless scaling parameters useful in characterizing multiphase flows are summarized along with experimental flow visualization techniques. Static and dynamic stability considerations are also included along with methods for stabilizing multiphase flows through surface modifications. Observed gas-liquid and immiscible liquid-liquid flows are summarized in terms of flow regime diagrams and the different flows are related to applications in chemistry and materials synthesis. Means to completely separate multiphase flows on the microscale and guidelines for design of scalable multiphase systems are also discussed.

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Chemical Engineering Journal • 2021

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Biosensors and Bioelectronics • 2009

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Environmental Microbiology • 2008

Summary It has been previously noted that mixed communities typically produce more power in microbial fuel cells than pure cultures. If true, this has important implications for the design of microbial fuel cells and for studying the process of electron transfer on anode biofilms. To further evaluate this, Geobacter sulfurreducens was grown with acetate as fuel in a continuous flow ‘ministack’ system in which the carbon cloth anode and cathode were positioned in close proximity, and the cation‐selective membrane surface area was maximized in order to overcome some of the electrochemical limitations that were inherent in fuel cells previously employed for the study of pure cultures. Reducing the size of the anode in order to eliminate cathode limitation resulted in maximum current and power densities per m 2 of anode surface of 4.56 A m −2 and 1.88 W m −2 respectively. Electron recovery as current from acetate oxidation was c . 100% when oxygen diffusion into the system was minimized. This performance is comparable to the highest levels previously reported for mixed communities in similar microbial fuel cells and slightly higher than the power output of an anaerobic sludge inoculum in the same ministack system. Minimizing the volume of the anode chamber yielded a volumetric power density of 2.15 kW m −3 , which is the highest power density per volume yet reported for a microbial fuel cell. Geobacter sulfurreducens formed relatively uniform biofilms 3–18 μm thick on the carbon cloth anodes. When graphite sticks served as the anode, the current density (3.10 A m −2 ) was somewhat less than with the carbon cloth anodes, but the biofilms were thicker ( c . 50 μm) with a more complex pillar and channel structure. These results suggest that the previously observed disparity in power production in pure and mixed culture microbial fuel cell systems can be attributed more to differences in the fuel cell designs than to any inherent superior capability of mixed cultures to produce more power than pure cultures.

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Journal of Power Sources • 2016

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Journal of Power Sources • 2011

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Journal of Power Sources • 2021

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Frontiers in Energy Research • 2019

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Biotechnology and Bioengineering • 2011

Abstract Next generation battery technology is rapidly evolving to meet the demand for higher power densities and smaller footprints through novel catalysts and battery architecture. We present a µ‐scale, biological fuel cell which utilizes microbial electricity generation enabled by microfluidic flow control to produce power. The new fuel cell, the smallest of its kind, with a total volume of 0.3 µL, produces scalable and controllable electrical energy from organic matter which is sustained through microbial respiration and laminar flow separation of the electrolytes. Electrical currents are dependent on specific biofilm formation on the anode, the concentration of electron donor, and a diffusion‐limited flow regime. A maximum current density of 18.40 ± 3.48 mA m −2 (92 ± 17 A m −3 ) was produced by Geobacter sulfurreducens , and 25.42 mA m −2 (127 A m −3 ) by Shewanella oneidensis . The µ‐scale biological fuel cell introduces the necessary small size and fuel flexibility for applications in vivo and in situ sensors which may be remotely deployed and self‐powered. Biotechnol. Bioeng. 2011;108:2061–2069. © 2011 Wiley Periodicals, Inc.

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Sustainable Energy & Fuels • 2019

Geobacter biofilms can be switched into different metabolic activity states and operate efficiently at low concentrations microfluidic three-electrode reactor.

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Langmuir • 2017

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International Journal of Hydrogen Energy • 2013

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Energy & Environmental Science • 2012

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Microbial Cell Factories • 2019

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Applied and Environmental Microbiology • 2003

ABSTRACT Previous studies have suggested that members of the Geobacteraceae can use electrodes as electron acceptors for anaerobic respiration. In order to better understand this electron transfer process for energy production, Geobacter sulfurreducens was inoculated into chambers in which a graphite electrode served as the sole electron acceptor and acetate or hydrogen was the electron donor. The electron-accepting electrodes were maintained at oxidizing potentials by connecting them to similar electrodes in oxygenated medium (fuel cells) or to potentiostats that poised electrodes at +0.2 V versus an Ag/AgCl reference electrode (poised potential). When a small inoculum of G. sulfurreducens was introduced into electrode-containing chambers, electrical current production was dependent upon oxidation of acetate to carbon dioxide and increased exponentially, indicating for the first time that electrode reduction supported the growth of this organism. When the medium was replaced with an anaerobic buffer lacking nutrients required for growth, acetate-dependent electrical current production was unaffected and cells attached to these electrodes continued to generate electrical current for weeks. This represents the first report of microbial electricity production solely by cells attached to an electrode. Electrode-attached cells completely oxidized acetate to levels below detection (<10 μM), and hydrogen was metabolized to a threshold of 3 Pa. The rates of electron transfer to electrodes (0.21 to 1.2 μmol of electrons/mg of protein/min) were similar to those observed for respiration with Fe(III) citrate as the electron acceptor (E o ′ =+0.37 V). The production of current in microbial fuel cell (65 mA/m 2 of electrode surface) or poised-potential (163 to 1,143 mA/m 2 ) mode was greater than what has been reported for other microbial systems, even those that employed higher cell densities and electron-shuttling compounds. Since acetate was completely oxidized, the efficiency of conversion of organic electron donor to electricity was significantly higher than in previously described microbial fuel cells. These results suggest that the effectiveness of microbial fuel cells can be increased with organisms such as G. sulfurreducens that can attach to electrodes and remain viable for long periods of time while completely oxidizing organic substrates with quantitative transfer of electrons to an electrode.

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Micro & Nano Letters • 2017

This work numerically investigated the effects of various factors on the performance of air‐breathing direct formic acid microfluidic fuel cells. An MFC with a microchannel width of 1.5 mm, depth of 0.05 mm, and electrode spacing of 0.3 mm was used in the simulation. An MFC which was a 1.5‐mm‐wide, 0.05‐mm‐deep microchannel installed with two 0.3‐mm‐apart electrodes was used in the simulation. The mixture of formic acid at concentrations of 0.3, 0.5, and 1.0 M and 0.5‐M sulphuric acid served as fuel, while a 0.5‐M sulphuric acid stream served as the electrolyte introduced at inlet flow rates of 0.05, 0.1, and 0.5 mL/min. First, a three‐dimensional MFC model was built using COMSOL Multiphysics 5.1 to simulate the fuel cell performance. Subsequently, I–V curves obtained from simulations and from published experimental data under similar operating conditions were compared to ensure the validity of the simulation. Transport phenomena were formulated with a continuity equation, momentum equation, species transport equation, and charge equation. Additionally, the flow through porous media in the gas diffusion layer was described using the Brinkman equation, whereas the Butler–Volmer equation was applied to obtain I–V and P–I curves. The current density distribution resulting from internal current loss and reactant concentration on both electrodes was also determined in this work.

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ChemPlusChem • 2020

Abstract A laminar flow reactor was designed that provides constant and reproducible growth conditions for the bioelectrochemical observation of electroactive bacteria (EAB). Experiments were performed using four reactors in parallel to enable the comparison of EAB growth behavior and bioelectrochemical performance under different hydrodynamic conditions while simultaneously keeping biological conditions identical. With regard to the moderate flow conditions found in wastewater treatment applications, the wall shear stress was adjusted to a range between 0.4 mPa to 2.9 mPa. Chronoamperometric data indicate that early stage current densities are improved by a moderate increase of the wall shear stress. In the same way, current onset times were increasing slightly towards higher values of the applied wall shear stress. Long‐term observations of EAB performance showed a decrease in current density and a leveling of the trend observed for the early stages of biofilm growth.

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Electrochimica Acta • 2022

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Journal of The Electrochemical Society • 2015

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Journal of Power Sources • 2022

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Physical Chemistry Chemical Physics • 2019

The electrochemical study of fast catalytic reactions is limited by mass transport using the conventional electrochemical cell with a rotating disk electrode (RDE).

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Journal of Power Sources • 2018

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ChemSusChem • 2012

Abstract We report a laminar flow‐based microfluidic bioelectrochemical system (BES) that was fabricated by using polydimethyl siloxane (PDMS) channels and gold electrodes. The microfluidic BES was operated as a potentiostatically controlled two‐electrode system. A pure culture of Geobacter sulfurreducens strain PCA, which is a model electrode‐respiring bacterium, was grown in the channel and respired with the electrode under strict anaerobic conditions. We took advantage of the short hydraulic retention time (≈2 min) and response times (<21 min) to rapidly test the effect of certain chemical stimuli, such as O 2 and anthraquinone disulfide (AQDS), on electric current production by G. sulfurreducens . The results showed that: i) short‐term (2 min) exposure to O 2 ‐saturated solution did not cause any irreversible toxicity to G. sulfurreducens , and ii) AQDS can be used as a redox mediator by G. sulfurreducens for shuttling electrons between the microbe and the electrode. We, therefore, demonstrate that the microfluidic BES is a promising research tool for gaining insight into microbial electrochemical activity. In our two‐dimensional microfluidic‐based research tool, a well‐defined electrochemical environment can be maintained with the help of laminar flow without a membrane to separate two electrodes.

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Lab on a Chip • 2011

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Frontiers in Microbiology • 2018

Microfluidic microbial fuel cells (MMFCs) are promising green power sources for future ultra-small electronic devices. The MMFCs with co-laminar microfluidic structure are superior to other MMFCs according to their low internal resistance and relative high power density. However, the area for interfacial electron transfer between the bacteria and the anode is quite limited in the typical Y-shaped device, which apparently restricts the current generation performance. In this study, we developed a membraneless MMFC with serpentine microchannel to enhance the interfacial electron transfer and promote the power generation of the device. Owing to the merit of laminar flow, the proposed MMFC was working well without any proton exchange membrane (PEM). At the same time, the serpentine microchannel greatly increased the power density. The S-MMFC catalyzed by Shewanella putrefaciens CN32 achieves a peak power density of 360 mW/m 2 with the optimal channel configuration and the flow rate of 5 ml/h. Meanwhile, this device possesses much shorter start-up time and much longer duration time at high current plateau than the previous reported MMFCs. The presented MMFC appears promising for biochip technology and extends the scope of microfluidic energy.

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International Journal of Hydrogen Energy • 2015