Electrochemical Detection - Waterborne Pathogens: Detection Methods and Applications - page 168

in steady-state, if the measured quantity is observed in time or frequency
domain, and if the analysis uses small or large amplitude signals as described
in Section 6.1 . Potentiometric-based detections have been presented in Sec-
tion 6.2 . With this technique, the biorecognition process is converted in a
potential signal. The technique has a very low limit of detection because the
response is a logarithmic value of the analyte's concentration. Few poten-
tiometric biosensors have been developed for the detection of pathogens.
Voltammetry has been introduced in Section 6.3 . In this technique, a time-
dependent potential or current is applied to the system, and the resulting
current or potential characterizing the biorecognition event is measured. Its
amperometric form is the most common electrochemical method, which
has been used for pathogen detection, and shows very high sensitivity. The
major advantage of coulometry is the absence of calibration procedure
because it is an absolute method based on Faraday's law, as presented in
Section 6.4 . This technique is mainly used for titration of solutions and
can be implemented for the kinetic study of respiratory processes of living
organisms. The ability of modern electronics to accurately measure and inte-
grate current-time functions permits coulometry to be applied even with
relatively small amounts of sample material. It requires a fine knowledge of
the underlying physicochemical mechanisms only known by experts and
has not been employed frequently for waterborne pathogen detection. The
integration of impedance with biorecognition elements for the detection
of pathogens (Section 6.5 ) has led to the development of many devices in
recent years. In impedance measurement, a controlled alternative potential
of a few millivolts is applied to the system over a wide range of frequen-
cies. It induces the flow of an electrical current, which depends on the
biological properties of the system. The detection limits of impedancem-
etry are still inferior compared to the others techniques. However, there
is a growing interest in this technique for biosensing and, in particular, for
waterborne pathogen detection because, contrary to previous techniques, it
is a label-free method. Dielectrophoresis (Section 6.6 ) has been used mainly
for manipulation (i.e. concentration, separation, and displacement) of mic-
roparticles and nanoparticles, including waterborne pathogens. Its use as a
characterization technique is not fully exploited, for time being, because
it requires the implementation of complex microsystems. We believe that
the current development of total analysis system technologies will allow
its broader use. The effects of scaling on the performance of these devices
have been reviewed in Section 6.7 . The small size is advantageous for por-
table or high throughput applications. However, we show that depending