Biosensors for the Detection of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 204

Figure 7.13 Schematic diagram of combined target molecular to antibody with gold
nanorods in SPR sensor. Source: Figure 2 from Ref. 63 . Reproduced with permission. (For
color version of this igure, the reader is referred to the online version of this topic.)
secondary antibody to increase the mass bound to the surface, improving
the LOD from 10 6 to 10 3 cfu mL −1 . 61 A commercially available Spreeta ™
SPR instrument was applied in 2007 to detect E. coli in matrices like milk
and apple juice with an LOD between 10 2 and 10 3 cfu mL −1 . 62 A later
SPR study for this pathogen incorporated gold nanorods into a standard
sandwich immunoassay, generating a fourfold improvement in sensitivity 63
( Fig. 7.13 ).
With regard to electrochemical biosensors, little work has been done
since the late 1990s when devices were developed with LOD of 10 2 -
10 4 cells mL −1 . 45 Amperometric and conductometric detection offered a
slightly lower LOD than potentiometric detection. In 2005, Radke and
Alocilja utilized immunocapture on a gold-coated electrode with imped-
ance detection to obtain an LOD of 10 4 cfu mL −1 in a 30 mL sample derived
from seeded lettuce.
Various mass-sensitive biosensors have been developed, including QCM,
QCM-D, PEMC, ME, and µC. Poitras and Tufenkji described a QCM-D
sensor for the detection of E. coli in 2009. While the LOD was similar to
the previous study, this work highlighted how the dissipation slope could
be a more accurate and rapid parameter to detect the presence of bacterial
cells 33 ( Fig. 7.14 ).
Campbell and Mutharasan have explored the potential of PEMC bio-
sensors with a variety of pathogens. The advantage of the PEMC setup
adopted by this group is the recirculating flow system, enabling the batch
processing of up to 1 L of water sample ( Fig. 7.15 ). For the E. coli immuno-
sensor, at a flow rate of 1.5 mL min −1 , the LOD was 1 cell mL −1 . 40