Biology Reference
In-Depth Information
Both QDs and fluorescent nanoparticles are less prone to the problems
of thermal fluctuations, self-absorption, self-fluorescence, and photobleach-
ing that traditional fluorescent dyes suffer from. QDs have the additional
advantage of a broad excitation spectrum with narrow emission bands.
Therefore, multiplexed detection of a range of pathogens, using one exci-
tation source is enabled. QDs have been functionalized with a range of
recognition elements, and applied to the detection of viruses, bacteria and
protozoa.
1,6,14,29
However, we found no reports of QDs specifically applied
to the detection of waterborne viruses.
QDs have been used in immunoassays for a range of foodborne bac-
teria, many of which are the same as waterborne pathogens, e.g.
E. coli
,
Salmonella
and
Shigella
.
14
In one case, QDs facilitated a 16-fold decrease in
sensitivity compared to fluorescein isothiocyanate (FITC) for the detec-
tion of
E. coli
.
30
The major advantage that QDs offer of easy multiplexed
detection have also been exploited for foodborne pathogens, with LODs
on the order of 10
2
-10
3
cfu mL
−1
comparable to those recorded in single
pathogen assays.
Single cell
E. coli
detection with QDs was reported by Hahn et al. in
2005, claiming two orders of magnitude with greater sensitivity than with
traditional organic dyes.
31
In 2006, Edgar et al. used QDs to specifically
detect
E. coli
in mixed bacterial samples to an LOD of 10 cells mL
−1
.
32
In
the same year, Yang and Li reported simultaneous detection of
E. coli
and
Salmonella
with an LOD of 10
4
cfu mL
−1
in under 2 h.
30
In 2007, the Chan
group demonstrated a multiplexed high throughput analysis microfluidic
system capable of rapidly detecting both
E. coli
and hepatitis, as a model
virus, in less than 1h and with 50 times greater sensitivity than existing
methods.
33
The detection system employed QD biobarcodes.
Su and Li adopted magnetic particles for sample processing in their 2004
study detecting
E. coli
with QDs.
34
The LOD was at least 100 times lower
than with FITC with a detection time of under 2 h. Zhao et al. who devel-
oped the multiplex foodborne pathogen QD detection described above,
used silica coated MNPs for enrichment of bacteria prior to detection,
35
as
did Agrawal in their circular microfluidic QD detection set up.
26
In 2007,
Liu et al. combined QD detection with a microporous immunofilter to
capture and identify
E. coli
, reaching an LOD of 2.3 cfu mL
−1
.
36
Dwarakanath and colleagues utilized a different approach involving
QDs for the detection of pathogens, quantifying the blue shift exhibited
upon bacteria binding.
37
The authors explained this shift by physical defor-
mation of the QD conjugates, as well as changes in the chemical environ-
ment, upon binding to bacteria. The intensity of the shifted peak grows
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