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A colorimetric method involving a novel gold nanoparticle-curcumin system is described for determination of melamine in urine. The natural phenol curcumin can reduce chloroauric acid to form well-dispersed gold nanoparticles, while at high concentration of melamine, reduction is suppressed and blue aggregates are quickly formed, which is confirmed by UV-vis spectroscopy and TEM images. The ratio of absorbances at 673 and 546 nm increases linearly in the 0.5 to 4 ppm melamine concentration range, and the detection limit is 0.16 ppm. The assay has been applied to analyze urine samples and showed recoveries with RSDs of <5%. The gold nanoparticle-curcumin based analytical system is simple for one-pot synthesis, convenient for visual detection and rapid requiring only 30 min. Therefore, it is a promising assay approach for melamine adulteration and well suited for homecare testing.