Rotating Droplet Hydrodynamic Electrochemistry for Water Toxicity Bioassay Based on Electron-Transfer Mediator

An electrochemical bioassay based on rotating droplet electrochemistry by using an electron-transfer mediator was developed for the evaluation of a wide variety of pollutants such as antibiotics, heavy metals, and pesticides in the water environment. Ferricyanide was used as an electron-transfer mediator for obtaining the catalytic response of Escherichia coli. The electrochemical response of E. coli was measured via hydrodynamic chronoamperometry in a microdroplet on a screen-printed carbon electrode (SPCE). The constructed electrode system successfully evaluates the catalytic response of E. coli solution in the presence of ferricyanide. An assay for antibiotic toxicity on E. coli was carried out. The EC₅₀ for ampicillin, sulfamonomethoxine, chlorotetracycline, tetracycline, and oxytetracycline evaluated by the pre-incubation method were 0.26, 0.77, 5.25, 18.5, and 19.0 µM, respectively. The toxicity order was ampicillin > sulfamonomethoxine > chlorotetracycline > tetracycline > oxytetracycline. The proposed method can be used to evaluate the antibiotic toxicities in different real samples, such as pond water, powder, and raw milk. Recoveries were found in the range of 90 and 99%. The developed methods do not require additional incubation time to evaluate toxicity.