Melamine Detection Based On Gold Nanoparticles Aggregation And Fluorescence Resonance Energy Transfer

Melamine is a nitrogen containing compound used in the manufacture of plastics. Because of its high nitrogen level (66% nitrogen by mass), melamine gives the analytical characteristics of protein molecules. Thus, melamine can be used to adulterate protein-rich diets by unethical manufacturers and resulted in the illness and death of people and pets. Melamine in food can be detected by high efficiency liquid chromatography (HPLC), gas chromatography (GC) /mass spectrometry (MS) and liquid chromatography/ mass spectrometry. However, most of the detection methods require expensive equipment such as MS or cost hours for detection result. Thus, developing a quick, inexpensive and sensitive method is required. Based on high affinity of cyanuric acid and melamine induced by hydrogen-bonding recognition, this paper developed the detection methods using nanoparticles.First, gold nanoparticles (GNPs) were synthesized by the reduction of HAuCl4 with sodium citrate and characterized using ultraviolet-visible spectrophotometer and high resolution transmission electron microscope (HRTEM). Then, 1-(2-mercaptoethyl)-1,3,5-triazinane-2,4,6-trione (MTT) were synthesized through regular organic synthesized methods. The MTT modified GNPs were obtained through ligand exchange reaction. Adding melamine into MTT modified GNPs caused aggregation and color change due to the hydrogen recognition between melamine and MTT. The influencing factor of melamine induced GNPs aggregation, including reaction time and concentration of melamine, were studied. Moreover, a novel assembled nanobiosensor FITC-Melamine-MTT-GNPs was designed to develop a quantity and sensitive melamine detection method. FITC was combined to melamine as fluorescence donor, and MTT modified GNPs as fluorescence receptor. Fluorescence quenching induced when two solutions mixed. When melamine added into the solution, a fluorescence recovery occurred. To further study the mechanism of FRET, quantum dots (QDs) were synthesized with mercapto ligand as the stabilizing agent in CdCl2 solution. Influencing factors such as reaction time and stabilizing agent were studied. The QDs were characterized through ultraviolet-visible spectrophotometer, fluorospectrophotometer, and HRTEM. Finally, the quantum dots were applied to melamine detection replaces FITC. To further study the quenching mechanism, the sensing approach which based on fluorescence resonance energy transfer (FRET) between CdTe QDs as an energy donor and GNPs as an energy acceptor was developed.Above all, this paper first successfully prepared the CdTe QDs and GNPs. Then, three melamine detection methods based on nanoparticles were developed. The first method based on melamine and MTT modified gold nanoparticles aggregation and effect of time and concentration were studied through ultraviolet-visible spectrophotometer. The second detection method based on FRET between melamine combined FITC and MTT modified GNPs. This method provides a potential way for quick, sensitive and quantities melamine detection. The third method based on FRET between melamine combined GNPs and MTT modified gold nanoparticles, which provide a potential way for the study of GNPs quenching mechanism.