Biology Reference
In-Depth Information
disadvantage of this method is that centrifugation is required in the sample
processing, making integration of this detection method into a continuous
flow system very difficult without the use of a different mechanism to label
and wash the cells. Interestingly, although the LOD was 100 oocysts mL
−1
,
the total volume injected into the sensor was only 20 µL (2µLmin
−1
for
10 min). Assuming an even distribution of oocysts through the buffer, this
would suggest that the number of bound oocysts was around two. This
technology could therefore detect clinically relevant levels of oocysts by
placing a greater burden on the sample processing stage that is currently
undertaken.
89
At such low flow rates, the sample must be concentrated
at least 500,000 times, which, without enrichment, would lead to a very
sparsely populated matrix, as other contaminants would also be concen-
trated. However, the problem of requiring extensive sample preparation is
not exclusive to SPR biosensing technologies.
The most successful approach for the detection of
C. parvum
with bio-
sensors is the use of PEMC, offering both the lowest LOD and largest
sample processing.
Cryptosporidium parvum
can be detected with PEMC
sensors not only in deionized water but also in phosphate buffered saline
(PBS) and other background matrices such as milk. Xu and Mutharasan
proved that such oocysts can be detected under a recirculating flow of
1 mL min
−1
both in PBS and in 25% milk in PBS background. Campbell
and Mutharasan achieved detection of
C. parvum
oocysts in PBS the range
of 100-1000 oocysts mL
−1
in less than 15min and suggested that detec-
tion of 1-10 oocysts mL
−1
could be possible.
38
Both experiments were
conducted in flow cell systems with sensor cell volumes of 120 and 90 µL,
respectively. However, sensitivity is reduced in the presence of interferents,
with a reported decrease in detection of around 45% in milk, and no test-
ing has yet been performed in finished drinking water.
39
The same authors
have utilized the same biosensor setup for detection of
Giardia lamblia
, with
an LOD of 1-10 cysts mL
−1
in 15 min in a variety of water matrices (buffer,
tap, and river water)
90
(
Fig. 7.19
).
There are very few reports of other protozoan biosensors. In 2004,
Wang et al. performed serological
Toxoplasma
detection based on the spe-
cific agglutination of antigen-coated gold nanoparticles, averaging 10 nm in
diameter, in the corresponding antibody and the resulting frequency change
is monitored by a piezoelectric device.
91
The year after, the same group
utilized enzymatic catalysis-induced precipitation of an insoluble product
monitored by EIS and cyclic voltammetry as well as QCM for serological
Toxoplasma
detection.
92
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