Melamine can be sensitively detected in aqueous medium through its selective interaction with polythymine (polyT_n) modified gold nanoparticles (AuNPs) by forming triple H-bonds, which results in aggregation of the polyT_n-stabilized AuNPs, displaying variations of localized plasmon resonance features such as colour change from red to purple and enhanced localized surface plasmon resonance light scattering (LSPR-LS) signals.