Electrochemical Detection - Waterborne Pathogens: Detection Methods and Applications - page 138

(a)

Cell monolayer

lon current

Changes in cellular
metabolism

Changes in
morphology

AC current

source Gold film

Gold film
electrode

counter
electrode
Phase sensitive impedance
measuremeant

Changes in
cytoskeleton

(b)

Figure 6.1 (a) Schematic representation of an electric cell-substrate impedance sens-
ing (ECIS) measurement system. Source: Adapted from Ref. 5 . (b) Schematic representa-
tion of the interaction between a target bacteria and a hybrid system aptamer-single
walled carbon nanotube. Source: Adapted from Ref. 6 . (For color version of this figure, the
reader is referred to the online version of this topic.)

So, when developing the application and thus having to choose the
technique to monitor these changes, one has first to wonder if one of the
phenomena has a much longer time constant that will impose its own
rate on the overall process and, second, if the corresponding phenomena is
indeed modified by the appearance of the pathogen in the system. Then,
one can choose the monitoring technique among various possibilities
where either the electrical voltage or the electrical current is imposed in
(non)-steady-state conditions and where the nonperturbed quantity (either
current or voltage) is observed in time or frequency domains. One can also
choose between large amplitude signal analysis and small amplitude signal
analysis. The techniques that use small amplitude signals (i.e. a few millivolts
peak-to-peak) on a polarization point assume that the response is a linear