A mediator microbial biosensor for assaying general toxicity

A mediator biosensor based on Paracoccus yeei bacteria for assaying the toxicity of perfumery and cosmetics samples was developed. An approach to selecting an electron-transport mediator based on the heterogeneous electron transfer constants for investigated mediators (k_s) and the mediator-biomaterial interaction constants (k_interact) was proposed. Screening of nine compounds as potential mediators showed a ferrocene mediator immobilized in graphite paste to have the highest efficiency of electron transfer to the graphite-paste electrode (the heterogeneous transfer constant, 0.4 ± 0.1 cm/s) and a high constant of interaction with P. yeei (0.023 ± 0.001 dm³/(g·s)). A biosensor for toxicity assessment based on the ferrocene mediator and P. yeei bacteria was formed. The biosensor was tested on samples of four heavy metals (Cu²⁺, Zn²⁺, Pb²⁺, Cd²⁺) and two phenols (phenol and p-nitrophenol). Proceeding from the EC₅₀ index, it was found that the use of the ferrocene mediator made the biosensor more sensitive to investigated toxicants than most analogues described. Toxicity determination of four perfumery and cosmetics samples by the developed biosensor showed prospects of using this system for real-time toxicity monitoring of samples.