It should be noted that the amount of phenolphthalein was
an important factor in a clear visualization of a color change.
Therefore, concentrations of phenolphthalein that varied from
0.01% to 1% were added to the detection reservoirs without the
addition of acid to the reaction reservoirs, and 0.1 and 0.01 M
NaOH solutions were applied to the center of the μPAD in
order to determine the optimal concentration for a clear
visualization of color change, as shown in Figure 1. Figure 1a