Rapid detection of Escherichia coli by flow injection analysis coupled with amperometric method using an IrO2–Pd chemically modified electrode

Abstract An amperometric method for the rapid detection of Escherichia coli ( E. coli ) by flow injection analysis (FIA) using an IrO 2 –Pd chemically modified electrode (CME) was developed in this paper. The method is based on a good marker β- d -galactosidase which was found in E . coli strains. β- d -galactosidase was produced by the induction of isopropyl β- d -thiogalactopyranoside (IPTG) and released from E . coli cells through the permeabilization of both polymyxin B nonapeptide and lysozyme to E . coli cells wall. The released β- d -galactosidase could catalyze the hydrolysis of the substrate p -aminophenyl β- d -galactopyranoside (PAPG) in the culture medium to produce 4-aminophenol which was proportional to the concentration of E . coli . Hence, E. coli could be detected by the determination of 4-aminophenol. An IrO 2 –Pd CME, which showed high sensitivity in determination of 4-aminophenol, was prepared as the electro-detector in FIA. The amplified response current of 4-aminophenol obtained at the IrO 2 –Pd CME was linear with the concentration of E . coli ranging from 2.0 × 10 2 to 1.0 × 10 6  cfu/mL, the detection limit of this method to E . coli was 150 cfu/mL and the complete assay could be performed in 3 h.