Nanotechnology for Detection of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 287

(a) (b)

Figure 9.3 Illustration of depletion effect in a mixture of two big bacteria plus small
rod-like cellulose nanocrystals. As the bacteria approach each other (a and b), rod-like
nanoparticles cannot enter the gap between the bacteria and bacteria flocculates.
Source: Figure 5 from Ref. 3 . Reprinted with permission. (For color version of this figure, the
reader is referred to the online version of this topic.)

were negatively charged but the CNC had a higher negative zeta poten-
tial than the bacteria. As bacteria get close, CNC rods can no longer enter
the gap between the big bacteria particles. Then, CNC rods push bacteria
together. Hence, CNC particles would be repelled from bacterial cells and
could be expected to flocculate the bacteria by depletion.”
There are many reports on the use of antibody-coated MNPs for separa-
tions linked to different detection formats of foodborne pathogens. How-
ever, this strategy is less common for waterborne pathogens. MNPs have a
large surface to volume ratio so they allow for high capture efficiencies. For
E. coli immunocapture, these beads were reported to reach 80%, compared
to 60% for ordinary paramagnetic beads. Varshney et al. reported captured
efficiencies of 94% in ground beef samples. 22 For foodborne pathogens,
simultaneous capture of pathogens as well as the use of aptamer functional-
ized MNPs have been reported, and have been linked to various methods
of detection including IR spectroscopy 23 and bioluminescence. 24 MNPs
have also been applied as the separation and concentration element in a
detection method called “biobarcodes”, described in Section 9.4.4 . One of
the major challenges with the MNP approach is the development of robust
surface chemistries for linkage of the MNPs to recognize elements. 14
MNPs have also been applied in conjunction with microfluidics, par-
ticularly with a circular microchannel set up. 25 The immunosensor chip
reported by Agrawal et al. in 2012 was fabricated with microdimensional