Biology Reference
In-Depth Information
ELISA-based biosensors using monoclonal or polyclonal antibodies
have also been tried. These biosensors show greater specific binding proper-
ties than enzyme-based methods; however, they can be limited by the need
for specific antibodies to be prepared for each compound to be detected, or
in this case, each toxin variant.
106
Electrochemical DNA sensors have received much attention in recent
years. They are simple, sensitive, specific, and relatively inexpensive. They
are based on the detection of DNA hybridization between the target
DNA and the probe DNA. This interaction causes some changes in
electrochemical properties that can be measured.
109
The electrochemi-
cal detection of
Microcystis
spp. was accomplished by immobilizing a
sequence-specific probe onto a transducer surface that is complimentary
to a specific gene sequence in
Microcystis
.
110
Methylene blue and ruthe-
nium complex was used as the electrochemical hybridization indicator.
Sensitivity of this method can be increased if samples are first subjected
to PCR to increase the species or gene-specific sequences that are used
as the target sequences.
Aptamers (short single-stranded DNA fragments) that can bind to target
molecules such as proteins, amino acids, and other molecules have also been
used to develop a surface plasmon resonance biosensor. These biosensors
can detect binding of MC to the DNA aptamer on the surface optically by
measuring the changes in refractive indexes.
111
Currently, no single biosensor has been validated for use in the detec-
tion of cyanobacterial presence in water sources. Possibly a combination of
immunosensors for the detection of the microcystin toxins released into
the environment, along with DNA/aptamer biosensors for the analysis of
gene sequences from
Microcystis
spp. to detect early algal bloom states, would
provide a well-coordinated effort to identify cyanobacterial pathogens in
water sources.
Biosensors for protozoan pathogens such as
Crytosporidium
have been
developed to detect oocytes using antibodies to the oocysts and piezo-
electric-excited millimeter-sized cantilevers as sensors.
112
They were
able to detect between 1 and 1000 oocysts mL
−1
, although a decrease in
detection was noted in the presence of contaminants in the samples that
can interfere with the signal, such as 45% milk.
113
Measurement of the
impedance instead of the resonant frequency of the cantilever was found
to reduce signal-to-noise ratio and improve the detection limits of these
sensors.
114
The use of antibodies for detection, however, is limited by
their specificity and the lack of ability to detect viability of the oocysts.
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