To demonstrate the utility of our approach, the developed
devices were evaluated for detecting Cu2+ in real samples,
including mineral water, groundwater, tomato, rice and blood
samples. Cu2+ was spiked into the samples at concentration levels
of 10, 50 and 100 ngmL1 and was measured using the developed
devices. The recovery results are shown in Table 2, the recoveries
and %RSDs of Cu2+ were found in the range of 92.60–119.01% and
0.87–9.16%, respectively, which suggests that this method is
reliable. In addition, the unknown samples were then determined
by both the developed method and the standard method, i.e.,
inductively coupled plasma optical emission spectrometry
(ICP-OES) (Table 3). The results from the developed method were
in good agreement with those from the ICP-OES method (paired
t-test at the 95% confidence level gave tcalculated (1.346) below
tcritical at t = 2.776 with 4 degrees of freedom). These results indicate
that the developed paper-based colorimetric sensor that is based
on the thiosulfate catalytic etching of AgNPls is applicable for Cu2+
detection in real samples.