Biology Reference
In-Depth Information
quicker than culturing techniques and easier to perform than molecular
methods. The authors suggest that PCR is a complex and costly analysis for
the underdeveloped countries that have the highest incidence of leptospiro-
sis. Molecular methods are described in more detail in Chapter 8.
5.1.1.1. Bacteria
In 2003, a commercially available (Analyte 2000, Research International)
fiber optic waveguide biosensor was applied using antibodies to capture
the bacteria and fluorescent labels for detection. Positive samples were then
subjected to further analysis using traditional culture methods or molecular
methods.
An alternative antibody-based indirect sensor with fluorescent labeling
was reported by Ho et al. in 2004. In this approach, capture antibodies were
immobilized on the interior surface of a microcapillary through which the
test sample subsequently flowed. Next, a liposome secondary antibody con-
jugate was passed through the capillary, followed by a rinse to remove any
unbound conjugate. The final detection step involved lysis of these lipo-
somes to release the encapsulated fluorescent molecules, giving a limit of
detection (LOD) of 360cellsmL
−1
in 45min. Liposomes can encapsulate
10
5
-10
6
fluorescent molecules, thus offering a means of signal amplification,
which resulted in the low LOD reported.
In 2005, Zhu et al. reported an LOD of 10
2
cells mL
−1
in 2 h for
Esch-
erichia coli
O157:H7 using a fluorescent sandwich immunoassay and fiber
optics for detection.
9
In 2011, U-bent optical fibers were adopted in an
attempt to improve the LOD. However, during the 20min allowed for
detection, detection of concentrations lower than 10
2
cfu mL
−1
was not pos-
sible due to diffusion-limited transport to the sensor surface.
10
Very recent
work has applied bacteriophages on optical fibers, with an LOD similar to
the previous reports of 10
3
cfu mL
−1
.
11
5.1.1.2. Protozoa
Raptor plus, a portable optical sensor developed by Research International
(Monroe, WA, USA), was tested for
Cryptosporidium
detection.
12
With a
detection mechanism similar to an immunofluorescent assay, described by
the authors as a fiber-optic biosensor, target oocysts are anchored on the
tip of an optical waveguide by antibodies binding and then washed with
reporter antibodies.
A laser diode is used to excite the fluorescence through an optical fiber
inserted in a miniaturized optical setup molded in a disposable polystyrene
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