Novel rapid detection of melamine based on the synergistic aggregation of gold nanoparticles

A simple and rapid colorimetric method for the detection of melamine in milk samples is described. Polythymidine oligonucleotide was adsorbed on to the surface of gold nanoparticles (AuNPs), protecting it from aggregation. In the presence of melamine, polythymidine oligonucleotide combined with melamine formed a double-strand DNA-like structure, allowing AuNPs aggregation. In the presence of positively charged SYBR Green I (SG I), AuNPs were further aggregated. In the presence of melamine and SG I, aggregation of AuNPs was synergistic. Thus, in this principle, melamine can be detected visually. Plasmon resonance peak changes enabled detection of melamine quantitatively using UV-vis spectroscopy. The limit of detection for this colorimetric method was 16 μg L^-1 with a good linear range from 19.5 μg L^-1 to 1.25 × 10³ μg L^-1, and detection took only 1 min. The method was successfully applied for detection of melamine in milk samples.