| Melamine is an important organic industrial material which is now widely used in making paint, plastic, adhesive, paper and other commonly used products. Because of the high nitrogen content of66%and low price, melamine has been illegally adulterated in dairy products to imitate protein in recent years. However, melamine is harmful to human’s health. A certain amount of ingestion of melamine into human body can cause trouble to reproductive system and urinary system, which has put forward an important issue for the detection of melamine in potable water and food. Nowadays, the most commonly used methods for melamine detection are HPLC, GC-MS, LC-MS, CE-MS and so on. Although these traditional methods for melamine detection are widely used, they usually need complicated pre-treatment or/and expensive detection instrument, leading to time extension of detection and/or increasing of detection costs. As more and more attention is being paid to food safety problem and the government’s stricter supervision of food safety, it is difficult for traditional methods to meet the need of both fast and simple detection of melamine. As a result, it is important to develop a fast, sensitive and selective method for melamine detection.In recent years, new methods for melamine detection are emerging. Of them colorimetry and fluorescent method are representative because they are fast, sensitive, selective and reliable, and the two methods are more and more widely used for melamine detection. In this study, colorimetric detection of melamine was based on the fantastic property of gold nanoparticles (AuNPs) and the interaction between AuNPs, poly-thymine (Tn) and melamine, and we fabricated a novel sensor with high-sensitivity and high-selectivity in water solution. The dispersion or aggregation of AuNPs was corresponding to the concentration of melamine with the help of UV-vis spectrometer. Fluorescent detection of melamine was based on the function of FRET (Fluorescence resonance energy transfer) on the surface of GO (Graphene oxide). When GO close approached to FAM (a kind of dye), fluorescence quench happened. When Tn labeled by FAM was combined with melamine, the configuration of DNA chain changed and DNA got away from the surface of GO, thus caused the recovery of fluorescence. Since the concentration of melamine was in proportion to the recovery of fluorescence in a certain range of concentration, the content of melamine could be determined by the recovery degree of fluorescence signal in fluorospectrophotometer. Our study has been proved sensitive and selective of melamine detection for both colorimetry and fluorescent method through the characterizations of AuNPs and GO, and the detection in water and real sample. In water samples under the optimum conditions, the linear range of colorimetric detection was from0.2×10-7mol/L to10.0×10-7mol/L, and the limit of detection (LOD) was0.011μmol/L. The linear range of fluorescent detection was from0.5×10-7mol/L to28.0×10-7mol/L, and the LOD was0.0066μmol/L. These two methods were both selective to the detection of melamine. For colorimetry, only a little interference was observed in10μmol/L ethanediamine and hexamethylene diamine to the detection of melamine, and no interference was observed in1μmol/L impurities. For fluorescent method, all impurities with the concentration of10μmol/L caused no interference to the detection of melamine. For the colorimetric detection in fresh milk and milk powder, the LOD were respectively0.15μmol/L and0.68μmol/kg. For the fluorescent detection in milk powder, the LOD was0.13μmol/kg. |
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