the impedance variation percentages (Bayoudh et al., 2008). This
trend corresponds to the increase of Δlog Z (%) obtained from
Bode plots. Beyond a concentration of 106 CFU/mL E. coli there is
no significant increase of Δlog Z (%) (data not shown) indicating
that the sensor surface reached a saturation point at concentrations
higher than 106 CFU/mL bacteria. Fig. 3b showed cyclic voltammograms
of the biosensor after each addition of bacteria. With
increasing bacteria concentrations, a decrease in the direct current
is observed due to the insulating properties of the bacteria attached
on the biosensor surface. A similar trend and saturation
conditions were observed for the other three bacterial strains, but
with different sensitivities (Fig. 3c). A notable increase of Δlog Z
(%) was observed after incubation of the sensor with 102 CFU/mL
bacteria. Therefore, this AMP based impedimetric biosensor can
detect bacteria at concentrations as low as 102 CFU/mL.