The Preparation Of Sensor Based On Nanoparticles And Its Application In The Detection Of Melamine

Melamine is a chemical raw material with low toxicity. There is a clear dose-response relationship between ingested dose of melamine and clinical disease. When excessive intake of melamine can cause kidney stones and can lead to kidney failure and even death. In this thesis, a magnetic relaxation switch（MRSw） assay and bimodal detection based on magnetic relaxation switch assay and UV-visible spectrum for melamine were reported. The main contents of this article include:（1） the design and synthesis of nanoparticles,（2） the synthesis of specific receptor cells, and the functionalization of nanoparticles by modified the cells to the surface of nanoparticles,（3） the detection of melamine by detecting the change of the signal. 1. Detection of melamine by a magnetic relaxation switch assay with functionalized Fe/Fe₃O₄ magnetic nanoparticlesFe/Fe₃O₄ magnetic nanoparticles（MNPs） were synthesized by the pyrolysis method via the precursor of iron pentacarbonyl under a nitrogen atmosphere,The obtained Fe/Fe₃O₄ MNPs showed the excellent dispersability in hexane with an averaged diameter of 10.8±0.5 nm. At the same time,（2,4,6-trioxo-1,3,5-triazin-1-yl） acetic acid（TTAA） were synthesized. Fe/Fe₃O₄ MNPs were modified with the dopamine conjugated with methoxypoly（ethylene glycol） carboxyl acid（m PEG-COOH） and（2,4,6-trioxo-1,3,5-triazin-1-yl） acetic acid（TTAA）（TTAA-Fe/Fe₃O₄ MNPs） through the coordination interaction between the dopamine and the surface of Fe/Fe₃O₄ MNPs to detect melamine in an aqueous solution. The magnetization value of TTAA-Fe/Fe₃O₄ MNPs was 58.7 emu/g. In this thesis, we reported a magnetic relaxation switch（MRSw） assay for melamine with TTAA-Fe/Fe₃O₄ MNPs. The approach of the MRSw assay for melamine is based on the aggregation of TTAA-Fe/Fe₃O₄ MNPs induced by the special triple hydrogen bonds between melamine and TTAA, which results in the increase of the spin-spin relaxation time（T₂） of surrounding water protons of nanoparticles. Due to no limitation of light scattering, the detection of melamine with the MRSw assay can be performed in a turbid medium without pre-treatment and purification. The change rate of △T₂ value（ΔT₂/T₂） increased 40 % upon addition of 30 μM melamine compared with that of the dispersed aqueous solution of TTAA-Fe/Fe₃O₄ MNPs（[Fe] = 32 μM）. With the concentration of melamine below 16 μM, the change of T₂ value has a good linear relationship with melamine. The excellent correlation coefficient（R2=0.9996） was achieved. Therefore, the quantitative detection of melamine can be performed in the concentration range of melamine below 16 μM, The limit of detection（LOD） for melamine is 2 μM. Furthermore, the MRSw assay exhibits a high selectivity for melamine over cytosine, uracil and thymine with the similar structure. 2. Functionalized Au-Fe₃O₄ nanocomposites as a Magnetic and Colorimetric Bimodal Sensor for MelamineAu nanoparticles（NPs） were synthesized in the presence of HAu Cl4（H2O）3 in the mixture solvents of 1,2,3,4-tetrahydronaphthalene（10 m L） and oleylamine（1 m L） in three-neck flask, which were used for the synthesis of Au-Fe₃O₄ composite nanoparticles（CNPs）. The Au-Fe₃O₄ CNPs were synthesis by the pyrolysis method via the iron pentacarbonyl on the surfaces of Au NPs in the presence of oleic acid and oleyamine under a nitrogen atmosphere. At the same time, l-（2-mercaptoethyl）-1,2,3,4,5,6-hexanhydro-s-triazine-2,4,6-trione（MTT）were synthesized. The Au-Fe₃O₄ CNPs was synthesised and it were functionalized with MTT through throng Au-S linkages. This Au-Fe₃O₄ composite nanoparticles contained optic and magnetic properties been from Au portion and Fe₃O₄ portion respectively. The approach of the bimodal detection for melamine is based on the aggregation of MTT@Au-Fe₃O₄ NPs induced by the special triple hydrogen bonds between melamine and MTT, which results in the red-shift of absorption position and the increase of the spin-spin relaxation time（T₂） of water protons. Upon additional melamine with different concentration to an aqueous solution of MTT@Au-Fe₃O₄ CNPs, the red-shift was observed and the colour of MTT@Au-Fe₃O₄ CNPs gradually changed initially from wine red, and finally to violet blue, the T₂ value increased obviously. Quantitative analysis was performed and the limit of detection（LOD） for melamine were 3.85 μM and 2.76 μM based on ways of colorimetric and magnetic detection, respectively. They were far below safety limit of melamine at 2.5 ppm for foods and at 1 ppm for powdered infant formula. Furthermore, the dual-modal method exhibits obvious selectivity toward melamine.