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of 3 × 10 5 to 10 7 oocysts mL −1 , using a flow rate of 50µLmin −1 . 34 The
flow was repeatedly stopped to allow time for the reagents to adsorb and
react (60 min for the oocysts). Furthermore, the influence of the back-
ground matrix on detection was tested in solutions containing either
biological interferents such as bacteria, particularly E. coli O157:H7 and
Enterococcus faecalis , or nonbiological ones such as latex microspheres or
humic and fulvic acids, commonly found in natural waters. A decline in
performance of up to 64% was measured depending on the interferent. 34
Poitras et al. also demonstrated that the initial slopes in f and D ( Fig. 7.17 )
could be used as a rapid means to detect oocysts, requiring just 5 min for
C. parvum quantification, when utilizing the initial slopes methodology. 34
The volume of solution held in the flow cell allowing 60 min for oocyst
binding was 40 µL.
Cryptosporidium parvum has been used as the target analyte in only two
SPR experiments to date, carried out by Kang et al ( Fig. 7.18 ). 86,87 The
LOD was highly dependent on the biological recognition strategy employed.
Using streptavidin-biotin for immobilization of antibody on the surface
followed by continuous oocyst flow gave a LOD of 1 × 10 6 oocysts mL −1 .
This high number is due to the low capture efficiency of the surface immo-
bilized antibody, which is a common problem for biosensors. 88 Decrease
of the LOD to 100 oocysts mL −1 was possible by labeling the oocysts with
biotin. This recognition strategy thus takes advantage of the high-affinity,
rapid reaction between the surface immobilized streptavidin and biotin. The
Figure 7.17 QCM-D measurements of the 1 overtone (a) frequency and (b) dissipation
shifts during physisorption of anti- C. parvum antibodies onto gold-coated quartz crys-
tals (phase I) followed by BSA adsorption (phase II). Source: Figure 1 from Ref. 34 . Repro-
duced with permission.
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