A reagentless electrochemical biosensor based on thionine wrapped E. coli and chitosan-entrapped carbon nanodots film modified glassy carbon electrode for wastewater toxicity assessment

An effective way to prepare the reagentless electrochemical microbial biosensor has been developed. First, the mediator thionine (TH) is wrapped on the surface of E. coli (E. coli@TH) through the simple electrostatic interaction, which makes E. coli and TH closely together and therefore shortens the electron transfer distance between the electroactive centers and the electrode. Then, E. coli@TH together with chitosan (CHI)-entrapped carbon nanodots (CNDs)are immobilized onto the glassy carbon electrode (GCE) surfaces to form the reagentless electrochemical microbial biosensor (CHI-CNDs-E. coli@TH), in which the CNDs are used to improve the conductivity of the modified electrode, and further enhance the electron transfer from E. coli to the electrode. The reagentless CHI-CNDs-E. coli@TH biosensor is finally used to evaluate the toxicity of four heavy metal ions (Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺) and three real wastewater samples, showing good performance in the evaluation of wastewater toxicity compared to other reported methods. This work opens up a new way for the preparation of reagentless electrodes, making it possible for electrochemical microbial biosensors to be equipped and realize on-line detection.