| With the development of nanotechnology and biotechnology, many novel nano- materials are playing important roles in bio-assays as new labels. Because of their special characters, superparamagnetic composite particles are more and more widely used in immunoassays. However, most of these applications focus in separation, concentration and purification of analytes in specimens, while their penetrating and high-sensitive magnetic signal is seldom involved.As a rapid and simple detection method, the technology of lateral flow immunoassays (LFIAs) has gained wide acceptance in a variety of fields since its initial development in the 1990s. But because of the limits of the signal particles used in it, LFIAs can not be performed as a high sensitive assay. Thus, it limits the development of LFIAs in the past ten years. Recently, superparamagnetic LFIAs have suggested us a new way to approach more sensitive immunoassays. The signal can be detected"in"nitrocellulose membrane, not like optical absorbance labels, can just be detected"on"the membrane, because of the penetrability of magnetism. It can reduce the influence by membrane surface nonuniformity, and makes the assay more sensitive and reliable. Moreover, magnetism signal itself can't be interfered by the color of test specimens, for example, whole blood and urine. Thus, some routine sample treatment courses, such as centrifugation of blood, extraction of urine, etc. can be avoided. And the test procedure is simplified. However, when we follow the routine procedures to prepare superparamagnetic composite particles, there are always some difficulties to give simultaneous considerations for the sizes, magnetism, stability, biocompatibility and labeling efficiency of the particles. These problems limit their applications on LFIAs. Furthermore, as a new signal labeling system, it has to be optimized thoroughly.Our studies took a different route to synthesize superparamagnetic composite particles to make them more suitable for LFIAs. First, Fe3O4/poly(St-co-MPS) composite particles were prepared by miniemulsion copolymerization of 3-trimethoxysilylpropylmeth- acrylate (MPS) and styrene(St). Subsequent growth of SiO2 layer by the conventional St?ber method allows the preparation of core-Shell superparamagnetic Fe3O4/poly(St-co-MPS)/SiO2 composite particles with controllable thickness of SiO2 shell. And then we made them carboxyl-functionalized on the surface with defined carboxyl density (MPs). The particles were highly magnetizable. And their saturation magnetization was as high as 45 emu/g at room temperature. Generally, they are sized-controlled, and has better biological compatibility, higher magnetism saturation, better condition tolerance, and more suitable for high sensitive magnetic LFIAs. The test signal can be read by superparamagnetic resonance reader (MAR, Quantum Design). Almost 100% of labeled analytes can be quantified through the whole thickness of membrane that makes the assay much more sensitive. Then, contents-controlled carboxyl groups were synthesized on particle surface. Finally, two surface-functionalized particles with high magnetism saturation and different carboxyl contents were achieved to study the improvement of labeling efficiency and detection sensitivity in next step.In chapter 3, we take human chorionic gonadotropin (hCG) detection as a model to study the application of magnetic composite particles we made and the optimization of the new system. The proper reaction time was determined as 20 minutes. Secondly, we regulated the surfactant and its working concentration for the system; Thirdly, the comparison on labeling efficiency and influence on sensitivity between two surface-functionalized particles with different carboxyl contents was done. The proper carboxyl content was determined. At last, the stability of the system was demonstrated by"aging process". In chapter 4, we take human hepatitis surface antigen (HBsAg) detection as a sample to evaluate our novel particles for"sandwich"magnetic LFIAs. PreS1 antigen was introduced into the preparation of monoclonal antibody against HBsAg to improve the specificity of the assay. Secondly, we added EDTA into the system to reduce the non-specific reaction during the assay. Finally we prepared our new magnetic LFIAs strips for HBsAg. And we assessed them by national standard specimens, the sensitivity was equal to ELISA kit, but with shortened test time of 20 minutes. Then, we performed clinical assessment at officially certificated sites, Beijing 302 hospital and Beijing Ditan hospital. Totally 849 serum samples were tested by our strips, and simultaneously compared with ELISA kits from Abbott, US and Kehua, China. Eventually, our strips reached the sensitivity of 100%, specificity of 99.2% and 99.9% of accuracy. These results are much better than other rapid LFIAs.In chapter 5, we take Clentuterol detection as a sample to develop"competitive inhibition"magnetic LFIAs strips by our novel particles. First, we synthesized BSA-clenbuterol antigen to improve the specificity of the assay. Second, we used new blockers to reduce the interference of related compounds in urine specimens. And the stability of the system was enhanced. For the final magnetic LFIAs strips for clenbuterol we made after the optimizations, we tested them by national standard sample. The sensitivity was 0.5g/L, equal to ELISA kit, but with shortened test time of 20 minutes. The assessment on testing swine urine was performed at Shenzhen Entry-Exit Inspection and Quarantine Bureau. Totally 107 samples were tested, and compared with colloidal gold LFIAs strips from Zhongde Biotech. Randox ELISA kit was taken as the judgment . The sensitivity of our strips was 100%, better than colloidal gold LFIAs system.After all the works we did, the novel superparamagnetic composite particles we made were demonstrated as a suitable material for magnetic LFIAs, both in"sandwich"and"competitive inhibition"types. And all the related optimizations can also be a useful reference for the development of other magnetic LFIAs. Moreover, some results and phenomenon we got in the study are good points for theoretical researches in the relationship between nano-materials and bio-molecules.
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