A Sensitive Voltammetric Biosensor for Escherichia coli Detection Using an Electroactive Substrate for b-D-Glucuronidase

In this paper, we developed a sensitive and simple electrochemical method for the rapid detection of Escherichia coli in water samples. The general principle of the assay utilizes the enzyme $\beta $ -D-glucuronidase. This enzyme was induced by adding methyl- $\beta $ -D-glucuronide sodium salt and its activity promoted the cleavage of 8-hydroxyquinoline glucuronide to the electroactive compound 8-hydroxyquinoline. This cleavage product was further oxidized on the working electrode of a potentiostat using cyclic voltammetry. The obtained current output signal in a specific voltage range (400 to 600 mV) indicated enzyme activity and subsequently was an evidence for E. coli cells in the sample. For our experiment, we designed a low-cost potentiostat and show an evaluation of this instrument. First, the $\beta $ -D-glucuronidase assay was tested with various concentrations of enzyme solutions before living E. coli cells were investigated. Our presented method allowed a clear and a sensitive identification of 1 colony-forming unit of E. coli without any interference from other investigated bacterial strains. Comprising only few working steps (filtration, incubation, and voltammetric analysis), the method allowed incorporation into an automated prototype that delivered results similar to those obtained from samples treated in laboratory.