Silver nanoparticles were prepared by the reduction of AgNO3 in dilute aqueous solutions of 4-nitroaniline. The effect of 4-nitroaniline concentration on Ag nanoparticles was investigated, and the sensitivity and selectivity of the prepared Ag nanoparticles solution on melamine presence in milk were also studied. The color change from yellow to blue with increasing melamine concentration was observed. The characterization methods used were transmission electron microscopy (TEM) and UV-Vis spectroscopy. TEM photographs indicate that the silver nanoparticles solution consist of well dispersed agglomerates of spherical shaped Ag nanoparticles with the average size of about 32nm. The Plasmon absorption peak for silver nanoparticles was found at 397nm. Also, it was revealed that a sensitive nonlinear correlation existed between the absorbance and the logarithm of melamine concentrations ranging from 50ppm to 10ppm

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