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

Abstract

The development of a simple and low cost electrochemical impedance immunosensor based on screen printed gold electrode for rapid detection of <i>Escherichia coli</i> in water is reported. The immunosensor is fabricated by immobilizing anti-<i>E. coli</i> 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 <i>R_ct</i> as the relevant parameter after the immobilization of antibodies, the blocking with BSA and the binding of <i>E. coli</i>. The introduction of a standard amplification procedure leads to a significant enhancement of the impedance increase, which allows one to measure <i>E. coli</i> in drinking water with a limit of detection of 3 × 10¹ 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 <i>R_ct</i> in terms of the "effective" electrode, which is modified by the detection of the analyte whose microscopic conducting properties can be quantified.