Biosensors for the Detection of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 207

spectroscopy to create an immunosensor capable of detecting 500 cfu mL −1
in 6 min. 70
Finally, in terms of mass-sensitive biosensors, QCM and µC Salmonella
biosensors have both been developed. In 2002, Wong et al. were able to dis-
tinguish between three serotypes (A, B, and D) of Salmonella and reported an
LOD of 10 4 cfu mL −1 . 71 This LOD was improved by two orders of magni-
tude by Su and Li in 2005 by the use of both a different mode of detection
(impedance measurements of motional resistance) and immunomagnetic
separation beads for amplification. 72 A bending mode µC achieved an LOD
of 10 6 cfu mL −1 whereas scanning electron microscopy (SEM) observations
indicated that signal was obtained with just 25 bacterial cells bound on
the surface. 73 This highlights a key problem with biosensing technologies.
While the systems may offer sufficient sensitivity to detect low numbers of
pathogens, the capture efficiency is often low, thus raising the LOD. A reso-
nant mode µC achieved an LOD of 5 × 10 3 cfu mL −1 , 74 and a recent paper
integrating a resonant mode µC with either microfluidic delivery or taking
a dip and dry approach reported LODs of 10 5 and 10 3 cfu mL −1 , respec-
tively. 75 The advantage of this latter work was that the µC signal was read
out using piezoelectric means rather than laser deflection, thus potentially
enabling portable devices.
7.5.3. Campylobacter
In terms of optical biosensors, fluorescence-based assays and SPR have been
employed for the detection of this pathogen. In 2004, a TIR fluorescence
sandwich assay was developed by Sapsford et al. 76 The LOD was reported to
be 10 2 -10 3 cfu mL −1 depending upon the strain and species of bacteria; the
difference was accounted for by variation in the antibody affinity for the vari-
ous different species and strains. In 2009, Bruno and colleagues reported an
aptamer-based quantum dot sandwich assay capable of rapidly delivering results
(15-20 min) using a portable, handheld fluorometer. 77 The LOD achieved was
as low as 2.5 cfu mL −1 , rising to 10-250 cfu mL −1 in food matrices.
In 2007, Wei and coworkers utilized SPR with capture based on anti-
bodies. 78 In this paper the authors found an LOD of 10 3 cfu mL −1 , which
was relatively low compared to other attempts at using SPR for bacteria. In
2011 the sensitivity of the SPR approach for Campylobacter was enhanced
by the use of a bacteriophage receptor binding protein as the recognition
element, enabling Singh and coauthors to achieve an LOD of 10 2 cfu mL −1 . 79
Ivnitski and coworkers developed an innovative amperometric biosensor
for the detection of Campylobacter . 80 The system uses a planar lipid bilayer