In conclusion, we show a simple method of spectroscopic
detection of Hg
ions in the water sample up to concentra-
tions as low as 10
M. Nanotriangles are thin, thermody-
namically unstable nanostructures with high energy sites at the
edges and tips and thus, their amalgamation tendency is
extremely high. The reduction of Hg
in the presence of these
gold nanotriangles selectively amalgamates gold at the tips and
edges. It is noteworthy that metallic mercury atoms do actu-
ally incorporate into the lattice of the triangles and also
effectively, but actually breaks off the amalgamated gold from
the edges and the tips, eventually damaging their morphology.
This process leaves a strong spectroscopic signature in the
optical absorption characteristic of the triangles and signiﬁcant
dampening in the longitudinal plasmon absorbance of the gold
triangles is observed up to femto-molar concentration levels of
mercury. We also show that this process is speciﬁc only to
mercury due to its strong tendency of amalgamation. The
method does not show any signiﬁcant change in the optical
absorption spectra of the gold nanotriangles exposed to
metallic lead up to 1 mM concentration. The HRTEM analysis
clearly conﬁrms that the action of mercury is mainly at the
tips and edges of the triangles. In addition, we also show the
budding off of amalgamated gold from the edges of the
triangles at some of the places, which further conﬁrm the
hypothesis that the amalgamation action is mainly at the edges
and tips of the gold nanotriangles. Thus, we show the mech-
anistic aspect of the amalgamation of the gold nanotriangles
leading to loss in their structural integrity, resulting in
a changed absorption proﬁle.
AS thanks the Council of Scientiﬁc and Industrial Research
(CSIR), Govt of India, for ﬁnancial assistance. We gratefully
acknowledge Mr Anubhav Bali and Mr Abhijeet Deo for
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3090 | Analyst, 2012, 137, 3083–3090 This journal is ª The Royal Society of Chemistry 2012