Electrochemical Detection - Waterborne Pathogens: Detection Methods and Applications - page 167

of four sensors with 4 µm wide interdigitated electrodes was manufactured
by optical lithography and metal deposition on a Pyrex substrate. The limit
of detection of the device was measured to be 10 4 oocysts mL −1 in the buf-
fer. Additionally, it was found that nonviable oocysts show a 15% difference
in impedance compared to viable oocysts at the same concentration of
1000 oocysts mL −1 . Evaluation of six single-stranded deoxyribonucleic acid
probes were performed by simulation and experiment as biorecognition
element of Bonamia ostreae and Bonamia exitiosa parasites showing that bio-
informatics can be used to developed genosensors. 160 Dielectrophoresis has
been applied to the study of both Cryptosporidium and Giardia (oo)cysts. It
has been shown that viable and nonviable oocysts electrorotate at different
rates and in opposite directions, depending upon the field strength. 64,161
Goater et al. designed a system in which traveling wave dielectrophoresis
was used to collect oocysts in the center of a spiral electrode, where electro-
rotation was applied for detection. In this work, it was observed that, in the
frequency window of 20-600 kHz, viable oocysts rotated faster than non-
viable ones, at rates discernible to the human eye or an automated image
recognition system. In 2010, a U.S. patent was granted to Simmons et al. for
the use of an insulating dielectrophoresis microfluidic chip to capture Cryp-
tosporidium . 162 The patent claimed that the device could process 1-10 mL of
water concentrating the sample to 25 µL for further study, such as immuno-
fluorescence. Potential clogging problems were addressed by the utilization
of an ultrafiltration membrane prior to sample entry into the dielectro-
phoretic segment. Recently, it was shown that Plasmodium falciparum tro-
phozoites modify the zeta potential of red blood cells, opening the way for
characterization of infectivity by measurement of zeta potential changes. 163
6.9. SUMMARY AND FUTURE OUTLOOK
Electrochemistry was issued from electrophysiology and developed by
important pioneer works in the first part of the twentieth century using
macroscopic electrodes. Electrochemistry moved into the micrometer-scale
world in the second part of the twentieth century. For the past 20 years, the
numerous electrochemical biosensors developed have demonstrated obvi-
ous interesting features for pathogen detection and analysis. They can be
classified into potentiometric, voltammetric, coulometric, impedimetric,
and dielectrophoresis, based on the observed parameter such as electrical
potential, current, charge, and dielectric properties. These different catego-
ries can be further refined depending upon whether or not the system is