Recently, colorimetric sensors based on noble metal nanoparticles
such as gold nanoparticles (AuNPs) [11] or silver nanoparticles
(AgNPs) [12] for the visual determination of Cu2+ have
gained increased attention. AgNPs is particularly of interest because
it has a higher extinction coefficient compared to AuNPs of the same
size and a lower costcompared toAuNPs [13]. Zhou et al. reportedon
the colorimetric detection of Cu2+ by using 4-mercaptobenzoic acid
(4-MBA) modified AgNPs. The measurement was based on the
aggregation of 4-MBA-AgNPs in the presence of Cu2+ via iontemplated
chelation [12]. Miao et al. proposed a colorimetric
detection method of Cu2+ with high sensitivity and selectivity by
utilizing the redox reaction between starch-stabilized AgNPs and
Cu2+ [14]. Ratnarathorn et al. presented the colorimetric measurement
on mPAD by using the homocysteine (Hcy) and dithiothreitol
(DTT)modifiedAgNP surface that is able to induce the aggregation of
AgNPs in the presence of Cu2+ [15]. In addition, a sensitive and
selective colorimetric method was developed based on catalytic
thiosulfate leaching of nanoparticles including silver coated gold
nanoparticles (Ag/Au NPs) [16] or AuNPs [17] by Cu2+. Cu2+ can
accelerate the leaching rate of NPs and leads to a dramatic decrease
in its surface plasmon resonance (SPR) absorption because the
nanoparticles size is decreased. Although these assays provided high
sensitivity, theyare time-consuming (25–60 min) and large volumes
of solution are required.
A paper-based sensor