Microfluidics for Biologists Fundamentals and Applications

For example, the hydrophobic channels of a paper-based microfluidic device that

is fabricated with wax or AKD will not allow the liquid to leak unless the surface

tension of the liquid is lower than a critical value. When the surface tension of a

liquid is lower than that value (e.g., biological samples with surfactant), liquid

can penetrate not only within the hydrophilic channels but also in the hydropho-

bic areas of the device, making the device ineffective for proper liquid transport.

3. Another challenge faced by researchers is how difficult it is to employ multiplex
   analysis using paper microfluidics. Though, a few multiplexed sensing studies
   have been performed; see Fig.6.8bfor an example. However, as the design and
   shape becomes more complicated, there is the potential for cross-talk as some of
   the signal reporters may diffuse to neighboring channels.
   A comparison of properties of different type of microfluidic materials is given in
   Table6.2.

exposed to an

artificial urine

solution containing

glucose and protein

Paper

μ-fluidic

element

Sample in

a Glucose

c

b

Lactate

Uric acid

5 mm

SPE

Fig. 6.8Examples of three detection methods for bioassays on paper-based microfluidic devices.
(a) Colorimetric detection for simultaneously detecting glucose and protein in an artificial urine
sample; (b) EC detection on a three-electrode paperfluidic device. (c) ECL detection of a sample
solution (2-(dibutylamino)-ethanol (DBAE)) [ 42 ]. Reproduced with permission from AIP
publishing LLC

6 Materials and Surfaces in Microfluidic Biosensors 159