Colorimetric Probes Based On Metal Nanoparticles For The Detection Of Melamine In Raw Milk

Gold, silver nanoparticles, as a typical representative of the noble metalnanoparticles, which possess many unique properties. Because of the good opticalproperties, electrical properties, magnetism properties and so on, gold nanoparticlesand silver nanoparticles have been widely applied in the fields of environment,medicine, biology, etc and been widely concerned by researchers. Melamine, a mainraw material of producing melamine formaldehyde resin in industry, because of itshigh nitrogen content, melamine was illegal added in dairy products by lawlesselements, therefore, a series of significant incidents of food raw materialscontamination broken out. Detection for melamine in food became a Key technologyof food safety testing. In this article, Au-NPs and Ag-NPs were used as colorimetricprobe, a simple, sensitive, rapid colorimetric method using label-free Au-NPs andAg-NPs as probe for detection of melamine in raw milk was developed based on thespecial interaction between Au-NPs, Ag-NPs and melamine. This study include thefollowing two parts:1、Au-NPs coated with citrate ions was synthesized used the traditional Frensmethod, the mechanism between Au-NPs and melamine was systemataciallyesplored. Au-NPs can be stabilized in aqueous solution by coating it withnegatively-charged citrate ions, and electrostatic force counteract the effects of Vander Waals’ force between molecules, with the result of homodisperse of Ag-NPs.when melamine was added into Au-NPs solution, the Au-NPs aggregated together,simultaneously, the color of Ag-NPs solution changed from wine red to purple. basedon this principle, a rapid, sensitive, simple method for melamine in raw milk wasdeveloped. This study systematacially optimized the detection conditions andestablished the optimum conditions. The linear coefficient R=0.9907，the detectionlimit for melamine is0.2mg/L(S/N=3).2、Compared with Au-NPs，Ag-NPs have some advantages, for example, lowercost of preparation, higher extinction coefficients relative to Au-NPs of the same size. Therefore, Ag-NPs are also good candidates for colorimetric probes of melaminesensing. Herein, a simple, rapid, economical and field-portable method has beenestablished based on the color change of label-free Ag-NPs for the screening ofmelamine. Under the optimized conditions, the absorption ratio (A500/A402) of thismethod exhibited a good linear correlation to melamine concentration in the range of4.0-170.0μM, the linear equation is：y=2.1096x+0.065, linear coefficient r=0.9989，the detection limit for melamine is2.32μM (3σ), which is well below thesafety limit (2.5ppm in USA and EU;1ppm for infant formula in China) ofmelamine ingestion.