| In recent years, because it has especial magnetic orientation and excellent biocompatibility, the applied research in the biological field of the superparamagnetic nanoparticles causes people's attention increasingly. Their are many investigative reports in targeted therapy of cancer/AIDS and other diseases, bioseparation, immobilization of enzymes or proteins, cell-based screening, nucleic acid purification and biological sensing, wastewater treatment, etc. It is expected that some nanoparticles have special functions integrate with the magnetic particles, which provide the magnetic particles with more functions. Among the total, quantum dots (QD) have the unique optical properties and have very far-ranging applications in the molecular markers, biological imaging, and ion detection, etc. The bifunctional nanocomposites with quantum dots' optical function and the superparamagnetic nanoparticles' high magnetic responsiveness are expected to play an important role in the biotical targeted markers, cell separation and screening, disease diagnosis and treatment. The main content of this article was the synthesis and characterization of the magnetic fluorescent bifunctional nanocomposites and their application in biology, details were as follows:1. The magnetic Fe3O4 nanoparticles were prepared by the improved chemistry coprecipitation method. The average diameter of the Fe3O4 nanoparticles was about 6nm-12nm as confirmed by TEM. The dispersivity of the nanocomposites were very good. We assigned the absorption band at 578cm-1 and 3421cm-1 tally with the standard Fe3O4 characteristic absorption peaks.2. The water-soluble CdTe quantum dots were prepared. Close analysis of the fluorescence spectrum shows that the emission wavelength is about 525 nm. And the CdTe quantum dots emit green fluorescence under UV irradiation.3. The SiO2-coated magnetic fluorescent bifunctional nanocomposites were prepared by the improved reverse microemulsion method. The average diameter of the bifunctional nanocomposites were about 15-20nm as confirmed by TEM. The dispersivity of the bifunctional nanocomposites were very good. The average diameter of the bifunctional nanocomposites were about 15-20nm as confirmed by TEM. The dispersivity of the bifunctional nanocomposites were very good, but partial agglomeration phenomenon was still existing. TEM, EDS and fluorescence detection showed that the magnetic particles and quantum dots were encapsulated into silica shell at the same time.4. The SiO2-coated magnetic fluorescent bifunctional nanocomposites were used to immobilize Glucose oxidase. The reaction condition for the immobilization of enzyme was optimized and the similarities and differences between immobilized enzyme and free enzyme were investigated. The result showed that, the optimal glutaraldehyde concentration of immobilized enzyme was 5%, the optimum immobilization time was 1 h, the optimal amount of enzyme was 2.5 mL, the optimal reaction temperature was 21℃, the optimal reaction condition was pH 5.5, Km value was 1.7 mg/mL. When the amout of enzyme was 2.0 mL, the reaction condition was pH 6.0, the reaction temperature was 24℃, the enzyme activity of immobilized enzymes was the best.5. Magnetic particles had the ferric ion that can be complexation with surrouding atoms, constructed a simple mimetic enzyme of HRP theoretically. In view of this, study it to be or not to take the place of HRP to involve in reaction as the mimetic enzyme. The results showed, the enzymatic reaction showed the lower enzyme activity instead of magnetic particles. It was explained that the magnetic particles can not catalysis H2O2 to form quinine imine that was measured absorbance as mimetic enzyme. However, this result ruled out the decomposition effect of dual-function material to H2O2 in the visual detection,made the results more credible.6. We observed the fluorescence changes, including the fluorescent bifunctional nano-material before and after adding hydrogen peroxide, the immobilized bifunctional nano-materials before and after adding hydrogen peroxide, the immobilized bifunctional nano-material before and after adding the glucose using the fluorescence microscopy. The result showed that, the magnetic particles and quantum dot are scoexistence in the silica shell, and hydrogen peroxide that glucose oxidase and glucose produced by the reaction has quenching effect on quantum dot's fluorescence, and the immobilized enzyme has some protective effect on fluorescence. Showed that the dual-function material can enrichment and fiuorescence detection glucose coinstantaneous.
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