Screen Printed Based Impedimetric Immunosensor for Rapid Detection of Escherichia coli in Drinking Water

The development of a simple and low cost electrochemical impedance immunosensor based on screen printed gold electrode for rapid detection of Escherichia coli in water is reported. The immunosensor is fabricated by immobilizing anti-E. coli antibodies onto a gold surface in a covalent way by the photochemical immobilization technique, a simple procedure able to bind antibodies upright onto gold surfaces. Impedance spectra are recorded in 0.01 M phosphate buffer solution (PBS) containing 10 mM Fe(CN)(6)(3-)/Fe(CN)(6)(4-) as redox probe. The Nyquist plots can be modelled with a modified Randles circuit, identifying the charge transfer resistance R-ct as the relevant parameter after the immobilization of antibodies, the blocking with BSA and the binding of E. coli. The introduction of a standard amplification procedure leads to a significant enhancement of the impedance increase, which allows one to measure E. coli in drinking water with a limit of detection of 3 x 10(1) CFU mL(-1) while preserving the rapidity of the method that requires only 1 h to provide a yes/no response. Additionally, by applying the Langmuir adsorption model, we are able to describe the change of R-ct in terms of the effective electrode, which is modified by the detection of the analyte whose microscopic conducting properties can be quantified.