2.3. Applicability of the PAD for clinical analysis
To evaluate the colorimetric assays on the PAD, the paper
device was designed to be a Y shape, which was composed of two
test zones (circular shape, 3 mm width) for the simultaneous detection
of glucose and protein. For the glucose assay, the reagent ratio
was adopted from Self-Stik reagent strips (Chungdo Pharm. Co.,
LTD, Korea). A volume of 0.5 L of a 10 mg mL−1 potassium iodide
solution was spotted onto the paper test zone and allowed to dry
for 5 min. Then, a 5 L mixture of 451 U mL−1 glucose oxidase and
186 U mL−1 peroxidase was dropped on the same test zone. For
protein detection, 0.5 L of 10×
bromocresol green (BCG) working
reagent [24] was dropped on the other test zone. Then, the paper
was allowed to dry at room temperature. To detect glucose and
protein, the bottom side of the paper devices was dipped in sample
solutions until colour developed at both test zones and could
be observed by the naked eye. The colour of the test zones on the
PADs were captured by a digital camera, and then, the colour
intensities were analysed using Adobe Photoshop CS2.