A mediator-free microbial electrochemical biosensor based on Escherichia coli nucleotide metabolism for rapid toxicity assessment of emerging contaminants.

To address the growing environmental risks associated with emerging contaminants and limited rapid toxicity assessment tools, we developed a mediator-free microbial electrochemical biosensor using Escherichia coli nucleotide metabolism. This biosensor enables the direct detection of electroactive metabolites without exogenous mediators by utilizing the oxidation peak current as a sensitive toxicity indicator. An electrode was modified with a nanocomposite of carboxylated multi-walled carbon nanotubes and zinc oxide (MWCNT-COOH/ZnO), which significantly enhanced the electrochemical signals. Mechanistic studies revealed that the detection signal originated from the oxidation of guanine and xanthine. The biosensor was used to detect four bisphenol analogues and two per-/polyfluoroalkyl substances. The toxicity followed the order of bisphenol AF > bisphenol A > bisphenol F > bisphenol S, suggesting that bisphenol AF posed a higher toxicity risk than bisphenol A. The half-maximal inhibitory concentration (IC50) for perfluorooctanesulfonic acid was 1011.13 μM, and its substitute, 6:2 fluorotelomer sulfonic acid, exhibited significantly lower toxicity at equivalent concentrations. The biosensor was further applied to actual water samples from the Yitong River, revealing generally low toxicity (inhibition rate <30 %) with higher inhibition rates observed at densely populated urban sites. This biosensor is characterized by simple operation, fast response, low cost, and independence from water turbidity or color, thereby offering an efficient and sensitive analytical platform for both toxicity assessment of emerging contaminants and safety evaluation of real water samples.