The Synthesis Of Luminescent Magnetic Nanoparticles And Their Applications In Bioanalysis

This paper focused on the synthesis, functionalization and the applications of magnetic nanoparticles and luminescent magnetic nanoparticles in the detection of hepatitis B surface antigen (HBsAg).Aqueous magnetite nanoparticles were synthesized by coprecipitation method. Magnetite nanoparticles had superparamagnetism with mean diameter of 15 nm, but they were not very stable under ambient conditions and tended to agglomerating. The shape of nanoparticles was spherical. Based on the rich hydroxyl groups, the surfaces of magnetite nanoparticles were modified with sodium citrate and dopamine. The result indicated that functionalization of magnetite nanoparticles with good dispersibility and stability could be achieved through modified with the concentration of 0.3mol/L sodium citrate. The amino-modified magnetite nanoparticles were obtained by using dopamine.Fe₃O₄@Au core-shell nanoparticles were synthesized by the method of Frens and their diameter was about 80nm. Fe₃O₄@Au nanoparticles had good magnetism. Their surface plasmon resonance absorbtion at the peak of 560-590nm of Au was found in the UV-Vis spectra. The frequency of the characteristic peak was enhancing with the thickening of Au shell. The reduction of HAuCl4 with THPC resulted in relatively small THPC-gold nanoparticles with a negative interfacial charge. The diameter of THPC-Au was about 4-5nm. We tried to obtain Fe₃O₄@Ag nanoparticles by adsorbing the negative THPC-Au to the surfaces of DA-Fe₃O₄ nanoparticles and then Ag shell were coated.Fe₃O₄/PE5/(QD/PDAC)3 nanoparticles were synthesized by layer-by-layer assem- bly of polyelectrolyte and luminescent CdTe quantum dots onto the surfaces of the magnetite nanoparticles. The method solved the problem that the fluorescence quenching of CdTe quantum dots caused by magnetite nanoparticles, but the process was tedious and timing-consuming. We synthesized Fe₃O₄@SiO₂ nanoparticles using improving St?ber method and CdTe quantum dots were adsorbed to the surfaces of the silica-coated magnetite nanoparticles. Finally the nanoparticles were coated with silica- shell. The diameter of Fe₃O₄@SiO₂/PDAC/QD@SiO₂ nanoparticles was about 100nm. The result indicated that luminescent magnetic nanoparticles with good dispersibility and stability could be used in bioanalysis.Based on the double antibody sandwich-type immunoassay, the residual fluoro- metric method for HBsAg detection has been established by using the carboxyl- modified magnetite nanoparticles as the carrier and carboxyl-modified europium nanoparticles as the fluorescent marker. Murine anti-HBsAg antibody was immobilized onto the surfaces of carboxyl-modified magnetite nanoparticles. Goat Anti-HBsAg antibody was immobilized onto the surfaces of carboxyl-modified europium nanoparticles. This method had the linear range 0.2-1.0μg/ml, the relation coefficient 0.9914 and the detection limit of quantification 0.2μg/ml. Based on above research,the direct fluorometric method for HBsAg detection has been preliminarily studied. The carboxyl-modified luminescent magnetic nanoparticles were the carrier and carboxyl- modified europium nanoparticles were the fluorescent marker. This method had the linear range 0.8-2.0μg/ml. But the sensitivity of the direct fluorometric method was lower than that of the residual fluorometric method. It provides a prospect application for detecting hepatitis B infectious disease in clinical medicine.