Nanostructured copper electrodes – a new step in the development of microbial bioelectrochemical systems†

This work proposes a new method for forming a biosensor based on a nanopillar copper electrode and microorganisms for rapid assessment of the biochemical oxygen demand (BOD) index. Heterogeneous electron transfer constants were obtained for water-soluble and insoluble redox-compounds, and single-mediator and dual-mediator bioelectrochemical systems were formed taking into account the obtained values. It was shown that the yeast Debaryomyces hansenii is not susceptible to the toxic effect of copper and could be effectively used with a nanostructured electrode in the ferrocene–methylene blue dual-mediator system. Paracoccus yeei bacteria are susceptible to the toxic effect of copper ions, therefore, their immobilization on the nanostructured electrode was carried out using the redox-active polymer poly(neutral red), which protects microorganisms from negative effects and allows effective conjugation of microorganisms with the surface. The developed bioelectrochemical measuring systems have high sensitivity (the lower limit of determined BOD₅ values is 2.0 mg dm⁻³) and high correlation with the standard method for BOD measurement in surface water samples (R² > 0.98). Thus, the work demonstrated for the first time the successful use of a metal nanopillar electrode as a substrate for the biosensor, and the created biosensor systems could serve as prototypes of commercially available miniature sensors for rapid assessment of water quality. The cost of the biosensor of the developed bioelectrochemical measuring systems was estimated: for a two-mediator system based on D. hansenii microorganisms and ferrocene–methylene blue mediators, the cost of one bioelectrode was 4.28 USD, and for a system based on P. yeei microorganisms and poly(neutral red) – 3.91 USD.