Aquamarine blue emitting silver nanoparticles as fluorescent sensor for melamine detection

Designing an exceptional probe to detect minute quantities of melamine is of huge importance for the safety and health of the human race. In this study, an aquamarine blue and rapid fluorescent sensor was devised by chemical reduction synthesis method for highly selective and sensitive detection of melamine in milk using polyethyleneimine protected silver nanoparticles (PEI-AgNPs). The optical properties of PEI-AgNPs were studied as a function of reactive material concentration, incubation time, temperature and pH. The formation of PEI-AgNPs was verified by using transmission electron microscopy (TEM) and found that the PEI-AgNPs were spherical in shape with an average diameter of 15 nm. The prepared PEI-AgNPs were aquamarine blue luminescent under UV light and show a maximum emission at 470 nm, when excited at 348 nm. The fluorescence of the PEI-AgNPs can be effectively quenched by the addition of melamine due to its ability to interact with citric acid (CA) through hydrogen bonding and form silver-melamine complexes with Ag⁺ via coordination bonds, while the addition of other nitro compounds induced feeble quenching of PEI-AgNPs, suggesting the high selectivity of PEI-AgNPs. The present sensor system exhibits a good linear response to melamine ranging from 0.16 to 56 μM, and the limit of detection was found to be 132 nM (Sb/K = 3). Significantly, the fluorescence sensor exhibited good selectivity and acted as a potential probe for detection of melamine in milk samples.