Colorimetric detection of melamine based on methanobactin-mediated synthesis of gold nanoparticles

A simple and rapid field-portable colorimetric method for the detection of melamine in liquid milk was reported. Methanobactin (Mb) could reduce Au (III) to Au (0) and mediate the synthesis of gold nanoparticles (Au-NPs). Upon the addition of melamine, melamine interacted with oxazolone ring of Mb, which interrupted the formation of Au-NPs. Melamine could also stimulate the aggregation of formed Au-NPs. In this paper, these characteristics have been used to detect melamine in liquid milk by naked eyes observation with a detection limit of 5.56 × 10−6 M (0.7 mg/kg). Further, the plasmon absorbance of the formed Au-NPs allowed the quantitative detection of melamine by UV-vis spectrometer. A linear correlation was existed between the absorbance and the melamine concentration ranging from 3.90 × 10−7 M to 3.97 × 10−6 M with a correlation coefficient of 0.9685. The detection limit (3σ) obtained by UV-vis spectrum was as low as 2.38 × 10−7 M (i.e., 0.03 mg/kg).