Miniaturized Detection Systems - Waterborne Pathogens: Detection Methods and Applications - page 321

Figure 10.4 Illustration of the two modes of hydrodynamic trapping of Cryptosporid-
ium oocysts. (a) Trapping in wells, view of the SUS micromesh and experimental set-up.
Source: Reprinted from Ref. 69 © 2001, with permission from Wiley InterScience . (b) Trap-
ping in filters, view of the prefilter structures and raindrop filter, inset A, inset B. Source:
Reproduced from Ref. 71 with permission of the Royal Society of Chemistry. (For color
version of this igure, the reader is referred to the online version of this topic.)
allowed the detection to be done in 60 min compared to 2-3 h claimed for the
IMS method (including staining) with automated fluorescein isothiocyanate
(FITC) labeling and imaging was used for detection. The LOD was reported
as 36 oocysts mL −1 , above the desired ability to detect single oocysts. 69
In 2001 Stokes and coworkers developed a sandwich immunoassay in
a 0.4 mL reaction chamber on-chip, demonstrating E. coli detection. In the
same year McClain et al. employed a microfluidic flow cytometry setup
for E. coli detection. Another microfluidic flow cytometer was developed
in 2004. 73 This device, made from PDMS, hydrodynamically focuses the
sample where it is excited and detected using optical fibers. The chip also
uses cheap, compact, and low-power PIN photodiodes with lock-in ampli-
fication to demonstrate the first single-cell fluorescence detection using this
type of photodiode. Device performance was characterized with beads and
yeast cells, with a sample volume of 5 mL h −1 , but has not yet been applied to
pathogen detection. Another sandwich assay presented by Li and Su in 2005
detected E. coli with an LOD of 10-100 cfu mL −1 in a 1 mL sample in 2 h,
claiming microfluidics allowed for an improvement of detection sensitivity
due to reduced reagent consumption and increased immunoassay kinetics. 74
In 2005, Sakamoto et al. also described a microfluidic flow cytometry
setup for E. coli detection capable of analyzing six 10 µL samples in just