Surface-enhanced Raman Scattering (SERS) microbial sensor for fresh water acute toxicity monitoring.

We present for the first time a SERS based microbial sensor for assessing acute freshwater toxicity. The assay is based on indole, which is synthesized in many Gram-positive and Gram-negative bacteria by L-tryptophan via tryptophanase (TnaA). In the presence of external toxic substances in the microbial growth environment, microorganisms' respiratory and metabolic functions are inhibited at varying degrees, leading to a decrease in indole production. We used SERS to monitor the conversion of L-tryptophan to indole and thus assess the toxic effects of toxic chemicals on E. coli. Two other factors affecting bacterial metabolism were also explored: L-tryptophan concentration and its incubation time with E coli. Copper was chosen as a simulated toxicant to assess the method's effectiveness for acute toxicity in freshwater. The IC 50 of Cu2+ was found to be 2.028 mg/L, which showed a significant improvement in sensitivity compared to other methods. [Display omitted] • A SERS based biosensor method for water acute toxicity evaluation was firstly proposed. • The method is based on the indole producing capability of E coli bacteria. • Acute toxicity assessed using indole concentration change upon introducing toxic chemical. • The toxicity of model ion Cu2+ was determined with an IC 50 of 2.028 mg/L. The substances emerging in environmental water bodies are becoming increasingly complex, causing severe ecotoxicological problems. In addition, the intricate interaction among various chemicals in a water body makes it difficult to accurately evaluate the water quality by simply determining the specie and concentration of the chemicals. Thus, acute toxicity evaluation of water body presents significant importance in environmental monitoring, especially in emergency response. This work proposes a SERS approach for evaluating acute toxicity of fresh water for the first time, where indole, an interspecies signal molecule produced by E. coli strains during regulated spore formation, could be affected by toxic substances, was used as indicator. Several key factors that may affect the evaluation of acute toxicity in water were explored, including the concentration of exogenous L-tryptophan and the incubation time of E. coli with L-tryptophan. Finally, the established system was applied to the acute toxicity evaluation of model chemical Cu2+. The IC 50 was determined to be 2.028 mg L-1, better than the results reported in the literature. This study demonstrates the feasibility of using SERS-based microbial sensors to assess acute toxicity in water. [ABSTRACT FROM AUTHOR]