Nanotechnology for Detection of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 301

serum, with the LOD rising to 10 in 100% serum. 88 Interestingly, for targets
larger than the NPs, such as bacteria, a nonlinear relationship between out-
put signal and bacterial concentration is observed with maximal sensitivity
for low bacteria concentrations ( Fig. 9.8 ).
An alternative magnetic approach was developed by Koets and co-workers
who used superparamagnetic particles as detection labels for DNA from
E. coli and Salmonella . 84 The MNPs were detected by a giant magnetoresis-
tance sensor. Using this system, 4-250 picoMolar amplicon concentrations
were detected in less than 3 min. Mukika et al. used a magnetorestrictive
immunosensor to measure E. coli O157:H7 in food and clinical samples,
Figure 9.8 Detection of viruses and bacteria using magnetic relaxation. An increase
in the concentration of the virus facilitates clustering of the nanoparticles and high
changes in the spin-spin relaxation times ( Δ T2). On the other hand, at low concentra-
tions of bacteria high Δ T2 are obtained due to nanoparticle assembly on the bacteria
surface. Δ T2 decreases as the bacterial concentration increases because the nanosen-
sors switch to a dispersed-like state, reminiscent of the one observed in the sterile
medium. Source: Scheme 3 from Ref. 1 . Reproduced with permission. (For color version of
this igure, the reader is referred to the online version of this topic.)