3.5. Analytical performance
The performance of the developed method was evaluated for
the quantitative detection of Cu2+. Under the optimized conditions,
the color intensity values of modified AuNPls at the detection zone
on paper-based devices were examined at room temperature in the
presence of Cu2+ in the range of 0–350 ngmL1. The pinkest of the
violet colors at the test zone changed to colorless after adding Cu2+
to over 0.1 ngmL1, and these results can easily be distinguished by
the naked eye as shown in Fig. 6a. The plots of the mean intensity
and concentration of Cu2+ show a reasonable linearity in the range
of 0.5–200 ngmL1 (R2 = 0.9974), with a LOD and LOQ of 0.35 and1.16 ngmL1, respectively (Fig. 6b), which is lower than that
obtained from the other nanoparticles. (Table 1). The obtained LOQ
values are lower than the maximum allowable levels of 1.30mg
mL1 in the United States for drinking water [3], and 2.00mg
mL1 in Thailand for surface water [4].