Facile electrochemical detection of Escherichia coli using redox cycling of the product generated by the intracellular β-D-galactosidase

Various detection methods for pathogenic bacteria have been developed, most of which are based on cell culture, DNA amplification, and immunoassays. Although the methods allow highly sensitive and/or selective detection, they require long detection periods and complex detection procedures. This paper reports a facile electrochemical detection method for Escherichia coli (E. coli) without the use of DNA amplification or immunoassays. The detection method harnesses the intracellular beta-D-galactosidase (Gal) activity of E. coli along with the signal amplification based on redox cycling. The Gal expression level is increased by treatment with a Gal expression-inducer (isopropyl-beta-D-thiogalactopyranoside; IPTG); the enzymatic reaction of Gal is facilitated by the permeabilization treatment involving the use of chloroform and sodium dodecyl sulfate; the electrochemical signal is amplified by the electrochemical-chemical-chemical (ECC) and chemical-chemical redox cycling involving the Gal product, Ru(NH3)(6)(3+) and tris(2-carboxyethyl)phosphine. The detection limit obtained in the presence of the ECC redox cycling, with a total detection period of only 4.5 h, is ca. 1 colony forming unit (CFU)/mL, indicating that ECC redox cycling allows for a sensitive detection. (C) 2014 Elsevier B.V. All rights reserved.