Heimdall in water quality monitoring: A novel antibiotic composite electrode for improving the sensitivity of biosensor
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Credit: Shuyi Wang, Xiang Qi, Yong Jiang, Panpan Liu, Wen Hao, Jinbin Han , Peng Liang
Water quality monitoring is recognized as an effective measure to guarantee water safety as it provides real-time information online and raises alerts for incoming pollutants. Among all the environment monitoring technologies, biosensor stands out for its ability to demonstrate the biological effects of pollutants and has attracted wide attention. Biosensors based on electroactive biofilm (EAB) have been intensively investigated in recent two decades as it enables water quality early-warning in real-life where most pollution incidents are unpredictable, showing a comprehensive and immediate response toward many kinds of substances.
Recent development emphasized that the biosensor with high sensitivity has massive value on the water quality monitoring, which is considered a major metric for the performance of EAB-biosensors. Several efforts have been made to increase the sensitivity through regulating operation condition of EAB-biosensors by adjusting external resistance, applied potential and current, employing transient state or open circuit mode, enhancing mass transfer between the biofilm and influent, as well as by modification of EAB and regulation on its microbial community by adding signal molecules. However, these regulation technologies are not convenient for practical engineering application and are limited to specific cases, leading to the lack of feasibility. For example, antibiotics have also been used as the agonist due to the promotion of the enrichment of electroactive microorganisms (EAMs) and adjustment of genes expression. However, the general antibiotics employed in recent studies were soluble species, which were not applicable or eco-friendly for water environment monitoring with continuous flow of feed water. As a result, insoluble antibiotics is urgently needed to enhance of the sensitivity of EAB for practical engineering application.
Therefore, with the purpose of regulating the biofilm thickness and microbial community of EAB for improving the sensitivity of EAB-biosensor, the researchers from Tsinghua University, Fujian Agriculture and Forestry University and Zhengzhou University used graphite powder (GP) with azithromycin (AZM), a kind of insoluble antibiotics, to form a novel AZM@GP composite electrode and to serve as the anode of EAB-biosensor. This study entitled “An antibiotic composite electrode for improving the sensitivity of electrochemically active biofilm biosensor” is published online in Frontiers of Environmental Science & Engineering in 2022.
AZM is a kind of insoluble antibiotics which belongs to macrolides group and establishes a major in-vitro antibacterial activity against aerobic Gram-positive cocci and Gram-negative bacillus. In this study, the novel AZM@GP composite electrode used as the anode of EAB-biosensor could affect the biofilm in the way that regulate the morphology and microbial community of EAB, then deliver stimulated sensing performance. The research team investigated the effects of improvement on the biosensor sensitivity with different antibiotic dosages. It was found that EAB-biosensor was greatly benefited from appropriate dosage of AZM (0.5% AZM@GP) with reduced start-up time period, comparatively higher voltage output, more readable electrical signal and increased inhibition rate (30%-65% higher than control sensor with GP electrode) when exposing to toxic formaldehyde. This may be attributed to the fact that AZM inhibited the growth of non-EAM without much influence on the physiologic or metabolism activities of EAM under proper dosage. It was found that azithromycin could increase the relative abundance of Geobacter and regulate the thickness of electroactive biofilm. Further investigation of the biofilm morphology and microbial community analysis suggested that the biofilm formation was optimized with reduced thickness and enriched Geobacter with 0.5% AZM@GP dosage.
This study developed a novel electrode applied in EAB-biosensor. Different from the conventional method, this electrode used the insoluble antibiotic as the agonist, which was applicable and eco-friendly for water environment monitoring with continuous flow of feed water in practice. This novel electrode is easily fabricated and equipped, therefore would be a promising way to facilitate the practical application of EAB-sensors.
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