Search

Inefficient extracellular electron transfer within bioanode leads to low current production by microbial fuel cell (MFC). In this study, magnetite was sprinkled in electroactive biofilm with the aid of magnet field. Magnetite located inside biofilm (interior-doped biofilm) facilitated the electron delivery of electroactive bacteria far away from electrode surface. Electron transfer efficiency was improved by 12% and 37% compared with that of biofilms with magnetite located at the interface of biofilm/electrode (surface-doped biofilm) and that without any magnetite (control biofilm) respectively. The output power density of MFC with interior-doped biofilm (764 ± 32 mW m −2 ) was greatly increased compared with that of MFCs with surface-doped biofilm (604 ± 22 mW m −2 ) and control biofilm (475 ± 12 mW m −2 ). SEM images showed that magnetite evenly distributed inside the interior-doped biofilm and penetrated the electroactive biofilm, which would facilitate extracellular electron transfer across electroactive biofilms and thus improving the bioelectricity production. [ABSTRACT FROM AUTHOR]

Advancing the application of bioelectrochemical systems necessitates the comprehensive understanding of electron transfer process in electrode-associated biofilm. While in situ electrical measurement by using the split electrode can illustrate the electron conduction in biofilm, the accuracy and interpretation of the obtained data is still in debate. Here, conductance of Geobacter sulfurreducens biofilm is measured by using the split electrode as substrate concentration is changed. Biofilm conductance decreases with the current production as the consumption of substrate. In addition, the measured conductance increases with the area of drain electrode (13.8 ± 1.8 μS for 0.5 cm2 and 29.4 ± 4.2 μS for 1 cm2). These results suggest the measured conductance of biofilm is influenced by microbial metabolism. This effect will diminish when the measurement is performed by using electrochemical impedance spectroscopy or under non-turnover condition. Our results provide the insight on the electrochemical origin of biofilm conductance determined by the in situ electrical measurement. • Biofilm conductance decreased with current production as consumption of substrate. • Biofilm conductance increased with the area of drain electrode. • The measurement of biofilm conductance was influenced by microbial metabolism. • Biofilm conductance significantly decreased under non-turnover condition. [ABSTRACT FROM AUTHOR]

Researchers believe that adding conductive mediums in electrochemically active biofilms (EABs) would improve the sensitivity of EAB-based biosensor for real-time water quality early-warning through facilitating the extracellular electron transfer (EET), which has been hardly evidenced mostly because naturally formed EABs employed in previous biosensor studies were recognized distinct and incapable of delivering comparable electrical signals. By preparing artificial EABs where Shewanella oneidensis MR-1 was encapsulated in sodium alginate (SA), this study solved how polypyrrole (PPy) as conductive medium would affect the sensitivity of EAB-based biosensor, as well as mass transfer of toxicant during this process. Different mass ratios (0.125:1, 0.25:1 and 1:1) of PPy over SA were tested, and the sensitivity promoted by 20%, 15% and 6%, respectively. Results indicated that a small amount of PPy addition (PPy: SA = 0.125: 1 in mass ratio) was more effective to increase the biosensor's sensitivity compared to larger amount of PPy employed in EAB. This was when improved conductivity introduced by PPy would dominate in affecting the sensitivity over contrarily weakened mass transfer in the meantime. • Artificial electroactive biofilms containing polypyrrole were prepared. • Polypyrrole increases conductivity as well as decreases mass transfer. • Small amount of polypyrrole better increased biosensor's sensitivity. [ABSTRACT FROM AUTHOR]

Revealing the pathways of electron transport within electrochemically active biofilms (EABs) is of great importance. Here, mixed-culture EABs are grown on three interdigitated microelectrode arrays (IDAs) with different gap widths of 10 μm, 20 μm and 50 μm and their conductances are determined. The maximum conductive current increases with the decrease of the gap width and charge transfer resistance obtained for the biofilm attaching on the electrode is 3–11 fold less than that for biofilm bridging gaps, suggesting high conductance of biofilm closer to the electrode surface. Results from Raman analysis show high abundance of multi-heme cytochromes in biofilm bridging 10 μm gap, leading to small resistance of biofilm growing on the IDA with 10 μm gap. In addition, the maximum conductive current of biofilm bridging gaps at the potential of −0.40 V vs. Ag/AgCl suggests that electron transfer in biofilm growing on IDAs is redox driven. All these results indicate the spatial heterogeneity of electron transport processes acting within biofilm. Biofilm conductance decreased with the increase of gap's width. Small resistance was found for biofilm adjacent to the electrode surface. Biofilm conductance was depended the abundance of multi-heme cytochrome. The process of electron transfer with EABs was spatial heterogeneous. Panpan Liu: Conducting a research and investigation process, writing the initial draft [ABSTRACT FROM AUTHOR]

• Summary of cutting-edge researches on microbial electrochemical sensor. • Discussion versatility and limitations of the traditional bioanode sensing element. • Highlight to explore spatial structure and interfacial electrochemical characteristics. • Suggestions for improving the bioavailability of toxic agents. • Potential challenges in field test for water biotoxicity monitoring. The development of low cost, convenient, and efficient biosensors is critical for water biotoxicity monitoring. Microbial electrochemical sensors employ electrode-biofilm as the sensing element, and detect biotoxicity by tracking the electron transfer between electroactive microorganisms and electrodes under toxic stress. Use of such biosensors in the aquatic environment can provide an early warning for the presence of various toxicants. In this paper, cutting-edge studies on strategies to create high performance microbial electrochemical biosensors are reviewed, which have mainly focused on different sensing elements. Bioanode sensing element-based microbial electrochemical sensors have been successfully applied in the laboratory to detect various toxicants, and to diagnose typical anaerobic wastewater treatment processes. The abiotic cathode sensing element is also included, which is mainly based on the electrochemical reduction of target analytes or its inhibition of the oxygen reduction reaction (ORR). The biocathode sensing element successfully solves the problems of low sensitivity and high false-negative rate, and recent advances and future perspectives in this field are highlighted. The limitations and potential solutions associated with the practical application of microbial electrochemical sensors for water biotoxicity monitoring are discussed. [ABSTRACT FROM AUTHOR]