Miniaturized Detection Systems - Waterborne Pathogens: Detection Methods and Applications - page 319

Giardia , developed by Ramadan and colleagues in 2010, 60 was described in
Chapter 4 (see Figure 4.5). In 2012, Agrawal et al. described a PDMS 3D
circular microfluidic system with imbedded permanent magnets, designed
for multiplex pathogen detection, where the first stage is capture of the
bacteria with immunomagnetic nanoparticles. 61
Early work using dielectrophoresis (DEP) to concentrate pathogen sam-
ples on a microfluidic chip was performed by Goater et al. in 1997, as part of
an electrorotation detection strategy for Cryptosporidium oocysts. 62 Electro-
kinetic separation of bacteria was reported by Cabrera and Yager in 2001. 63
In 2005, Gomez-Sjoberg reported DEP-based concentration of E. coli in
400 pL chamber, achieving concentration factors of 10 4 -10 5 . 64 In 2011,
Chow and coworkers reported a DEP system for trapping and concentrat-
ing E. coli . 2 The system operated at a flow rate of 1 µL min −1 and claimed
a 100% trapping efficiency if an appropriate DEP force was chosen. Addi-
tionally, different voltages could be applied to distinguish between different
species and viable and nonviable microorganisms.
Insulator-based DEP (iDEP) was first described in 2005 by Lapizco-
Encinas. 65 Later iDEP was demonstrated in a plastic chip for the capture
of E. coli by Cho et al. in 2009. 66 At a flow rate 100 µL min −1 their sys-
tem achieved a maximal capture efficiency of 66%. This seems relatively low,
especially in comparison to IMS though it is comparable to recovery rates
following membrane filtration and elution. It is obviously unlikely to be
sufficient for reliable detection of single organisms. A 2011 thesis reported
the design of 3D iDEP systems for trapping of bacteria, reporting stronger
trapping forces at lower temperatures, reducing the risk of thermal damage
to the trapped cells, thus potentially enabling further downstream analysis. 67
This work represents the first observation of intraspecies differences in mem-
brane surface properties using iDEP. One potential problem with DEP or
iDEP as a concentration and isolation technique is that it operates in batch
mode which could complicate integration into continuous flow systems.
Taguchi and coworkers have investigated the microfluidic trapping
of protozoa, for subsequent fluorescence analysis. 68 They developed a
microwell array strategy, consisting of 32 × 32 microfabricated wells with
a 10 or 30 µm diameter and a 10 µm depth, for oocysts capture. After
microfabrication, the microwells were selectively coated with streptavi-
din and anti- Cryptosporidium parvum antibodies. For capture experiments,
10 mL of a sample mixture of C. parvum oocysts (10 7 oocysts mL −1 ) sus-
pended in phosphate buffered saline (PBS) was simply deposited onto the
array and the whole chip rotated horizontally for 1 h.