Bio-polyphenols promoted green synthesis of silver nanoparticles for facile and ultra-sensitive colorimetric detection of melamine in milk.

Green, simple and quick melamine sensing assays for highly efficient detection of melamine down to nM level have been reported. Biopolyphenols (rutin & curcumin) were used as reducing and stabilizing agents for the synthesis of silver nanoparticles (AgNPs). The synthesis of AgNPs was confirmed by FTIR, UV-Visible, XRD and HRTEM-EDS analysis. The biopolyphenols reduced AgNPs were well dispersed and spherical in shape. However, the presence of melamine in the reaction medium disrupted their synthesis. This may be attributed to interaction of melamine with Ag ions and biopolyphenols. At low concentration of melamine, pale red colored solution was obtained owing to formation of aggregated mass of AgNPs, whereas, at high concentration of melamine, colorless solution was obtained indicating disruption in synthesis of AgNPs. The presented protocol was proposed in light of optical responses, UV-Visible plots and HRTEM-EDS analysis. Using the sensor assays, good limit of detection, 0.01 ppm (79 nM) and 0.24 ppm (1900 nM) by Ag-Rutin and Ag-Curcumin respectively, were obtained. The detection limits offered by both sensing assays were quite lower than safety level recommended by regulatory bodies (20 μM in the USA and EU, 8 μM for infant formula in China). The sensing assays displayed good selectivity as well as sensitivity. The proposed sensor was successfully deployed for detection of melamine in raw milk samples.