Demonstration of labeless detection of food pathogens using electrochemical redox probe and screen printed gold electrodes

The demonstration of a labeless immunosensor for the detection of pathogenic bacteria using screen printed gold electrodes (SPGEs) and a potassium hexacyanoferrate(II) redox probe is reported. Gold electrodes were produced using screen printing and the gold surfaces were modified by a thiol based self assembled monolayer (SAM) to facilitate antibody immobilisation. SAMs based on the use of thioctic acid (TA), mercaptopropionic acid (MPA) and mercaptoundecanoic acid (MUA) were evaluated. Following antibody immobilisation via the optimum SAM, the redox behaviour and diffusion co-efficient (D) of the potassium hexacyanoferrate(II) probe was monitored in the absence and presence of analyte. In the presence of analyte, a change in the apparent diffusion co-efficient of the redox probe was observed, attributable to impedance of the diffusion of redox electrons to the electrode surface due to the formation of the antibody-bacteria immunocomplex. No change in the diffusion co-efficient was observed when a non-specific antibody (mouse IgG) was immobilised and antigen added. The system has been demonstrated with Listeria monocytogenes and Bacillus cereus. (C) 2002 Elsevier Science B.V. All rights reserved.