In general, a key conceptual
development of metal nanoparticles based colorimetric assay is the modification of its
surface. Ligand-modified surface of AgNPs have been increasingly explored for selective and
sensitive detection of metals of interest [13-16]. Aminothiols are widely applied as ligands
for such modification because sulfur-containing compounds can be easily bound onto the
surface of AgNPs [17]. The addition of target metal results in the aggregation of AgNPs,
followed by the changes in color and absorption spectrum [18]. For example, Ratnarathorn et
al. used homocysteine (Hcy) and dithiothreitol (DTT) to modify AgNPs for detection of Cu2+
in water [19]. Vasimalai et al. developed a method for detection of Hg2+ using
mercaptothiadiazole capped AgNPs [20]. Li et al. used glutathione stabilized AgNPs to
selectively detect Ni2+ [21]. Shang et al. developed a colorimetric detection of Ni2+ using Nacetyl-
L-cysteine-functionalized AgNPs [2]. Based on these previous approaches, the
detection limit of Ni2+ is somewhat inadequate for certain applications. Consequently, our
objective in this work is to develop a modified AgNPs sensor for a facile, selective and
highly sensitive detection of Ni2+.