Research Specifications

Melamine (1,3,5-triazine-2,4,6-triamine) is an organic compound that serves as raw material for the production of melamine resins. As melamine contains a high level of nitrogen (66% by mass), the illegal addition of melamine to dairy products can lead to significant enhancement of protein content that is measured by using the Kjeldahl method. In this assay, one-step synthesized silver nanoparticles with C-dots as the reducing and stabilizing reagent were employed for visible and fluorescent detection of melamine in raw milk. C-dots played an important role in reducing silver ions and stabilizing the nanoparticles. When C-dots were added to the silver ions in alkaline solution, monodispersed AgNPs would be obtained, resulting in remarkably reduced fluorescence emission. Aggregated AgNPs were observed when melamine was present. Visual color changes corresponding to the UV−vis absorption spectra were observed. Moreover, the fluorescence signals would be increased with the further increase of melamine. As a result, a dual optical platform combined UV−vis absorption and fluorescence signals could be achieved through the addition of melamine into the system. However, in the presence of melamine, silver ions could interact with the nitrogen atoms in amine and triazine groups of melamine. With 0-2 µM melamine, aggregated AgNPs were found after the reduction by C-dots, resulting in color and absorbance changes. With further increase of mel amine (2-20 µM), both formation and aggregation of AgNPs were inhibited, and the fluorescence was gradually increased. The results for melamine assay based on visible and fluorescent method showed the requisite sensitivity with a low comparable detection limit, as well as high selectivity.