Amperometric method for rapid detection of Escherichia coli by flow injection analysis using a bismuth nano-film modified glassy carbon electrode

A new method for rapid detection of Escherichia coli (E. coli) was developed by flow injection analysis (FIA) using bismuth nano-film modified glassy carbon electrode (BiNFE) in this paper. The method depended on a good marker β-d-glucuronidase which is found in E. coli strains. β-d-Glucuronidase was produced by the induction of methyl-β-d-glucuronide sodium (MetGlu), then released from E. coli cells through the permeabilization of cell membrane caused by polymyxin B nonapeptide and lysozyme. The released β-d-glucuronidase could catalyze the hydrolysis of the substrate 4-nitrophenyl β-d-glucuronide (PNPG) in the culture medium to produce 4-nitrophenol. Since 4-nitrophenol is electroactive and its quantity is proportional to the concentration of E. coli, E. coli could be determined by electroanalysis of 4-nitrophenol. The BiNFE was fabricated by an electrodeposition of metallic bismuth onto a glassy carbon electrode, which showed a high sensitivity in determination of 4-nitrophenol when used in conjunction with FIA system. Experimental results showed that the amplified response current of 4-nitrophenol obtained at the BiNFE was linear with the concentration of E. coli ranging from 1.5 × 10² to 1.0 × 10⁶ cfu/ml, the detection limit of this method for E. coli is 100 cfu/ml, and the complete assay was performed in 3 h.