Biomedical Engineering Reference
In-Depth Information
Fig. 10 Paper-based microfluidics. a Paper-based H-filter. Reproduced from [
75
] with permis-
sion of The Royal Society of Chemistry. b Colorimetric urine analysis Reprinted with permission
from [
67
]. Copyright (2009) American Chemical Society. c Microzone paper plates with ELISA.
Reprinted with permission from [
11
]. Copyright (2009) American Chemical Society. [
12
].
d Three dimensional networks in paper [
66
] Copyright (2008) National Academy of Sciences,
U.S.A
paper-based microfluidics (Fig.
10
)[
67
]. Here the fluids are contained within
hydrophilic channels made of chromatography paper bounded by hydrophobic bar-
riers (Fig.
10
b). Fabrication of the patterned structures using wax printing or pho-
tolithography techniques is relatively straightforward [
67
]. Chromatography paper is
widely available and inexpensive, resulting in a cost of less than $0.01 per device.
They require no external pumping systems because the natural wicking property of
the paper passively transports the fluidics along the channels. Moreover, paper is
already well established in lateral-flow immunoassays, providing detection of
labelled antibodies or analytes [
80
,
83
]. Building on this pre-existing technology, the
progress in paper-based microfluidic research has accelerated in the last few years.
Recently the H-filter has been shown to work in paper-based microfluidic
devices [
75
]. Here the principle is the same, but the fluidic channels are replaced
by a nitrocellulose membrane cut into channels. The fluids containing the mole-
cules absorb into the material and move down the length of the channel network
via the membrane pores. Figure
10
a shows how it is possible to separate the dye
tartrazine from Blue-BSA [
75
]. The main channel widens at the end to maximise
the interdiffusion zone to further spatially separate the different-sized molecules.
Content of the two regions can be analysed by cutting the paper, vortexing them in
water, and measuring the absorbance of the solutions. In this case, an enrichment
factor of 64 times was achieved. Apart from the reduced costs, the other advantage
of a paper-based pretreatment system is that pumps and external power are not
