| Since Watson and Crick put forward the famous double-helix model of DNA structure in 1953, the study of nucleic acid has entered a new developing period. For example, DNA recombinant technique has attracted widespread attention. These technical breakthroughs greatly promote the development of other subjects. The quantitative analysis of nucleic acid is of great importance in life science, biochemical medicament, clinic medicine and food analysis. At present, there are many methods for determination of nucleic acid, such as probe technique, absorption spectrophotometry, fluorescence spectrophotometry, chemiluminescence and new developed resonance light scattering. The resonance light scattering technique is a new tape of light scattering analysis technique which used common fluorescence spectrophotometer with simple operation and high sensitivity and has been widely used in analysis and determination of nucleic acid, protein, drug and carbohydrate.We investigated the interaction mechanism of bisbenzimide and nucleic acid by resonance light scattering. Besides that, we took advantage of fluorescence emission and light scattering ratio method, combining with fluorescence property of bisbenzimide to establish a new analysis method for nucleic acid with good stability. The main contents are as follows:1. Hoechst 33258, named bisbenzimide, is a derivative of bibenzimidazole and polycyclic aromatic hydrocarbons with low molecular weight. It has electrochemistry -active properties and can specifically interact with DNA, which can be used as suitable electroactive indicator for hybridization. The spectrum of resonance light scattering confirmed that there is electrostatic interaction between bisbenzimide and DNA. Meanwhile, the absorbtion spectrum indicated that the interaction of bisbenzimide and DNA is intercalative binding and the main binding sites is A-T pair region of DNA.2. Gengeally only one signal was usually used with fluorescence spectrophotometry or resonance light scattering. As to the system with both fluorescence emission and light scattering signals, we intend to simultaneity take advantage of the two signals to improve the sensitivity, detection range and resistivity to the external interfere. Therefore, for these biological particles with both fluorescence and light scattering signals, we can measure the ratio of different optical signals at certain wavelength and establish fluorescence emission and light scattering ratio method. Hererin, based on the enhanced resonance light scattering and fluorescent quenching effect of DNA to organic dye Hoechst 33258, we establish a fluorescence emission and light scattering ratio method for determination of DNA. Experiments showed that in buffer of pH 4.56, the ratio of enhanced resonance light scattering at 352 ran and quenching fluorescent emission at 500nm are proportional to the concentration of fish sperm DNA (fsDNA) and over the range of 0.04-1.6μg/mL, with the correlation coefficients of 0.9935 and the limits of determination (3a) of 5 ng/mL. The method is simple, fast and can resist to the external interfere, which was successfully used for the determination of DNA in synthetic mixtures.3. Flow cytometry(FCM), which developed from last 70th, uses light scattering and emission of fluorochrome molecules to generate quantitative, rapid, and specific multi-parameter data for detection and analysis from particles and cells. FCM can detect the size of cell, content of DNA or RNA, antigen on the cell surface and so on. On the other hand, nano-drug has many particular advantages such as good stability, low gastrointestinal irritation, little toxic and side effects, high bioavailability and good targeting effect and sustained release function. We studied the slow release effect of BSA nanoparticle after it interacted with CTC. only mix BSA nano-particle and CTC then incubate with S.a immediately ,we found that after 6h interaction ,cell damage and death ratio is obvious higher than the comparison which not only mix BSA nano-particle and CTC but also agitate them 24h, this phenomenon suggests that BSA nano-particle acting as a vector for CTC exhibits Slowly Releasing Effect.
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