Nanotechnology for Detection of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 300

NPs to further amplify the signal, achieving an LOD of 2 × 10 3 cfu mL −1 , a n
improvement on traditional QCM results. Mao et al. have also used NPs as
mass enhancers to amplify the frequency shift for this bacteria reporting a limit
of 2.67 × 10 2 cfu mL −1 . 82 In terms of detection of bacteria cells, Olsen et al.
employed nanosized phages as the recognition element for the rapid detection
of S. typhimurium , with a detection time of less than 180 s reaching an LOD of
10 2 cells, and giving a linear response in the range 10-10 7 cells mL −1 . 83
9.4.4. Molecular methods
Many of the ways to utilize nanotechnology to enhance the detection of
pathogens described in other sections of this chapter can also be applied to
the detection of molecular targets, and indeed some examples have been
given under the other sections, e.g. optical methods, 2,33,48 electrochemi-
cal detection, 73 SPR, 76 QCM detection of bacteria, 81-83 and magnetic
approaches. 84 AuNP interactions with DNA for surface plasmon peak
shifts were described in the 1990s as a method of molecular detection, 1 and
CNTs have been shown to protect oligonucleotide sequences from deg-
radation. 14 The use of nanomaterials in molecular methods has been har-
nessed in many examples, 1 although as yet the applications to waterborne
pathogen detection remains a relatively underexploited target market.
Biobarcodes are an emerging nanobiotechnology for molecular detec-
tion of pathogens. 14 In these assays, signal amplification is achieved using a
DNA reporter molecule. First, the target is concentrated with antibody or
aptamer coated NPs and, second, an NP coated in short DNA “barcode”
stretches is applied to facilitate sensitive detection. This is achieved due to
the multiple copies of the barcode per nanoparticle, and in one report the
LOD was lowered by 10 6 times compared to a conventional enzyme-linked
immunosorbent assay (ELISA) method. 14 This approach has been applied
for the detection of norovirus in food samples, 85 as well as E. coli O157:H7
in water. 86 In the latter example, an LOD of 25 cfu mL −1 , or 87 gene copies
for double stranded DNA, was reported.
9.4.5. Magnetic detection
Nanotechnology has also enabled novel detection strategies, such as the
magnetic relaxation switch approach developed by Perez et al. 87 In this set-
up, antibody carrying dextran coated iron-oxide NPs alter the spin-spin
relaxation of adjacent water molecules upon target recognition. The results
can be read out using a benchtop magnetic relaxometer. This has facilitated
the detection of as few as five viral particles for adenovirus in 10 µL of 25%