Electrochemical Detection - Waterborne Pathogens: Detection Methods and Applications - page 156

positive consequence is that the ohmic drop of potential is decreased,
and measurements in lower conductivity media are possible. A negative
consequence is that the current is not measurable, and it is then necessary
to work with arrays of electrodes to improve the absolute current level.
The small size of the electrodes permits measurements in very limited
volumes or at very short distances allowing a high collection efficiency
of analytes. A detailed description and a demonstration of these scaling
effects can be found in Refs 36 and 37 for integrated planar electrodes
(voltammetry, coulometry, and impedancemetry) and in Ref. 38 for ion-
sensitive field-effect transistors (ISFETs) (potentiometry).
As a consequence, much effort has been devoted in the recent years
to apply electrochemical techniques to microscopic scales. All of the
above-described techniques have been miniaturized. The well-established
integrated circuit and the emerging microelectromechanical system tech-
nologies provide the possibility to create a variety of miniaturized devices
dedicated to the detection of (bio-)chemical analytes and microorganisms.
Potentiometric sensors have been reported using the metal-oxide sensi-
tive field-effect transistor, 39 the light-addressable potentiometric sensor
(LAPS), 40 ISFETs, 41,42 and ISEs. 43 Amperometric sensors utilizing either
flow-by or stopped flow analysis have been adapted to diverse applications
including biosensing, 44,45 gas sensing 46 and chlorine. 47 Coulometric sen-
sors have been constructed for the measurement of chemical oxygen in
lake water. 48 The study of mediated enzyme reactions by rapid coulometric
methods has also been reported. 49 More recently, it has been shown that
very precise release of calcium ions from ion-selective membranes can
be controlled by electrical current. 50 A very robust implementation of
a coulometric chip showing low deviation and high reproducibility has
also been reported. 51 Many promising applications of impedance spec-
trometry have been reported; for example, for counting and character-
izing suspended cells in microchannels ( Fig. 6.7 ) 52-54 or for monitoring
physiological changes (migration, proliferation, apoptosis, etc.) in cell
cultures or small tissue samples. 55-59 Cerrioti cleverly took advantage of
the benefits offered by these different techniques to realize an integrated
system monitoring in parallel acidification rate, oxygen consumption,
and cell adhesion, respectively, with potentiometric, voltammetric, and
impedimetric biosensors. 60 Dielectrophoresis has been implemented in
numerous microsystems to transport, separate, concentrate, or characterize
microparticles and nanoparticles. 61 The electric fields utilized in dielec-
trophoresis have either been generated by patterned external or internal