Electrochemical Detection - Waterborne Pathogens: Detection Methods and Applications - page 166

Campylobacter jejuni detection was performed with an enzyme-linked immu-
noassay coupled with a tyrosinase-modified enzyme electrode. 149 Recently,
Li reported on an amperometric immunosensor, which uses gold nanopar-
ticles to enhance surface area. The device was tested with E. coli O157:H7
bacteria and have a working range, under optimal conditions, of 4.12 × 10 2 -
4.12 × 10 5 colony-forming units per milliliter. 150 Immunomagnetic separa-
tion was performed to isolate C. jejuni from the sample solution. This system
was evaluated using C. jejuni pure culture and poultry samples inoculated
with C. jejuni . In recent years various kinds of electrochemical biosensors
based on the identification of the bacterial nucleic acid have been devel-
oped. Legionella pneumophila 151 and Vibrio cholera 152 have been detected
and quantified by combined polymerase chain reaction and differential
pulse voltammetry. Wang developed genosensors for Cryptosporidium , E. coli ,
Giardia , and Microbacterium tubercolosis based on the immobilization of
specific oligonucleotides onto a carbon paste electrode and chronopotenti-
ometry for monitoring the hybridization events. 153 Baeumner described the
development of a field-usable RNA biosensor for the detection of viable
E. coli in water. Bacteria were thermally lysed, and mRNA was extracted,
purified, amplified, and quantified. A detection limit of 5 fmol per sample was
determined for a synthetic target sequence. 154 Radke described a high den-
sity microelectrode array biosensor for the detection of E. coli O157:H7. 155
The biosensor was fabricated from (100) silicon with a 2 µm layer of ther-
mal oxide as an insulating layer and an active area of 9.6 mm 2 and consisted
of an interdigitated gold electrode array. The change in impedance caused
by the bacteria attachment to the electrode surface was measured over a
frequency range of 100 Hz-10 MHz. The biosensor was able to discriminate
between bacterial concentrations of 10 4 -10 7 cfu mL −1 in pure culture and
inoculated food samples. More recently, Maalouf showed that the detection
limit can be decreased to 10 cfu mL −1 . 156 The development of a disposable
immunochip system has been described by Li. 157 It used electrochemical
impedance spectroscopy and fluorescence microscopy to study the detec-
tion of Legionellosis .
Reybier used electrochemical impedance spectroscopy to monitor the
changes affecting murine macrophage cell line in response to parasite infec-
tion by Leishmania amazonensis and proposed a model describing the inter-
action of the parasite with the host cell metabolism. 158 Electrochemical
impedance spectroscopy has been used to detect Cryptosporidium in water. 159
In this example, the release of ions from Cryptosporidium oocysts results in a
change of conductivity in a water buffer. A chip consisting of an arrangement