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Abstract
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We developed a convenient, label-free, and
nonaggregation-based silver nanoparticles probe for colorimetric
detection of melamine. Ag nanoparticles (AgNPs) were
synthesized using gallic acid, known as 3,4,5-trihydroxybenzoic
acid, as a reducer and stabilizing agent simultaneously at
room temperature. The formation of AgNPs was confirmed by
various technical analyses, for example, UV?vis spectroscopy,
Fourier transform infrared spectroscopy, energy dispersive
spectroscopy, elemental mapping, powder X-ray diffraction, Xray
photon spectroscopy, dynamic light scattering, and highresolution
transmission electron microscopy. Since the gallic
acid has three hydroxyl groups, it can interact with melamine
via several hydrogen bonds which has been confirmed with theoretical study by density functional theory; thus, in the presence
of melamine, the free gallic acid as a responsible agent for the synthesis of AgNPs, is decreased. Consequently, the formation of
silver nanoparticles is disrupted because reducers are not enough for the reduction of Ag ion. Simultaneously, the color and
spectral changes of the AgNPs depend on melamine concentration such that lower melamine concentration is equivalent to
yellow (high absorbance) and higher concentration corresponds with colorless solution (low absorbance). In this way, the
plasmon absorbance of AgNPs at 400 nm can be used for quantitative measurement of melamine. Our finding indicated that a
sensitive linear calibration curve can be obtained between absorbance at 400 nm and the logarithm of melamine concentration
in the range of 0.04?20 ?M with a linear coefficient of 0.992. The assay conveys a detection limit of 3.609 nM ± 0.014 (3?)
and shows high potential for melamine detection in a selectivity study.
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