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As serious water ecological pollution caused by toxicant leakage occurs frequently, early-warning for toxicity presented in water environment attracts increasing attentions as it saves time to retain water safety and human health. Electrochemically active biofilm (EAB) sensor is a promising device for in situ real-time water toxicity early-warning. To improve the sensitivity of EAB sensor particularly for low-concentration toxicity warning, this study employed titanium mesh (TiM) as the anode to construct an EAB sensor. Compared to traditional EAB sensor with carbon felt (CF) anode, the sensitivity of the TiM sensor was increased up to 37.4 times. The effects of mesh size (TiM50, TiM100, TiM150) and operation mode (flow-by and flow-through) on the sensitivity of TiM sensors were further investigated. Results showed the sensor with TiM100 anode had the highest inhibition rate (IR) in flow-by mode, attributed to low charge transfer resistance (R ct) and fast mass transfer. Flow-through operation could further enhance TiM100 sensor's sensitivity from flow-by operation and succeeded to signal as low as 0.0025% formaldehyde, the lowest so far tested in EAB sensor with sensing anode. Multiple toxicity shocks on flow-through TiM100 sensor revealed its good recoverability towards all tested formaldehyde concentration from 0.01% to 0.0025%, during which electrochemical activity degradation and biomass accumulation partially impaired the repeatability. This work highlights the great improvement of EAB sensors by utilizing titanium mesh as EAB carrier and provides a reference for the practical application of metallic materials for EAB sensors. [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]