Microfluidics for Biologists Fundamentals and Applications

Amplification) and colorimetric detection of a malaria DNA sequence [ 70 ]. Paper
based micro-fluidic device has also been used in detection of uric acid, glucose
using gold nanoparticles [ 71 ].
Dengue viral has been diagnosed using the conventional techniques like PCR
(polymerase chain reaction) and ELISA (enzyme-linked immunosorbent assay)
[ 72 ], even these methods are highly accurate but they need a highly clean lab and
expert people to perform the test. In the developing countries like, India where the
lab facilities are not appropriate in all the locations especially in rural areas, the
paper based detection can play a complementary role. Yen et al. [ 73 ] developed a
paper based testing device which can give a patient a diagnosis within few minutes
on whether they have dengue, Ebola or yellow fevers. The red, green and orange
silver nanoparticles were immobilized to the respective antibodies that bind the
spiked proteins. These antibodies were then attached to a small piece of paper.
Instead of whole blood samples, salivary fluid has also been used for dengue
detection because it is an important source of biomarkers and is useful for rapid
point-of-care diagnostics. Salivary fluids carries the immunoglobulins (e.g., IgGs
and IgMs), lymphocytes and plasma cells, which may serve as biomarker in point of
care diagnostics. But major limitation of salivary fluid as a sample is that it cannot
be applied directly to commercially available lateral flow test strips because it
causes the non-specifically binding of conjugated particles to the nitrocellulose
membrane. To overcome this problem, Yi et al. [ 65 ] recently developed a rapid test
for the detection of anti-DENV IgG in saliva. They introduced samples and reagent
in separate flow paths. The sample flowed through a matrix of fiber glass which
reduces the non-specific adhesion caused by the salivary substances. Figure2.22
shows the design of device for dengue detection.
The device gave good results in saliva samples spiked with IgG but requires
further improvement to detect IgG extracted directly from the blood of dengue-
infected patients. To improve the sensitivity (It is the ability of a paper based assay
test to correctly recognize patients who have a given disease or disorder.) and

Malaria pLDH

Anti-pLDH Gold Nanoprobe

TX-114 Micelle

20 min

Sample Mixed with Micellar

Aqueous Two-Phase System Simultaneous Concentration & Detection

Fig. 2.21 Schematic diagram of paper based device for malaria detection in a single step
(Reproduced from Pereira et al. [ 68 ] with permission from the Elsevier)

2 Microfluidics Overview 59