Two kinds of electrochemical impedimetric biosensors for the detection of E. coli O157:H7 are described and compared. They were fabricated using self-assembled layers of thiolated protein G (PrG-thiol) on (i) planar gold electrodes and (ii) gold nanoparticles (Au NPs) modified gold electrodes. The fabrications of the biosensors were characterized using cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy and atomic force microscopy techniques. The modification of the planar gold electrode by Au NPs via self-assembled monolayer of 1,6-hexadithiol as a linker molecule increased the electrochemically active surface area by about 2.2 times. The concentration of PrG-thiol and its incubation time, as well as the concentration of IgG were optimized. The Au NP-based biosensor exhibited a limit of detection of 48 colony forming unit (cfu mL-1) which is 3 times lower than that of the planar gold electrode biosensor (140 cfu mL-1). It also showed a wider dynamic range (up to 107 cfu mL-1) and sensitivity. The improved analytical performance of the Au NP-modified biosensor is ascribed to the synergistic effect between the Au NPs and the PrG-thiol scaffold. The biosensor exhibited high selectivity for E. coli O157:H7 over other bacteria such as Staphylococcus aureus and Salmonella typhimurium. Graphical abstract Schematic representations of sensor fabrication using Au NP-modified electrode (HKEC = heat- killed E. coli O157:H7).
Keywords: Biosensor; E. Coli; Electrochemical impedance spectroscopy; Gold nanoparticles; Oriented antibody immobilization; Pathogen detection.