| DNA analysis is the technology to reveal the biological characteristic in molecular and genetic level; it is the most effective and convenient way for research in life sciences. So, the study of DNA analyzer is very important; it is the source of the information. The laser induced fluorescence DNA analysis system was researched and developed. Two detection systems were designed and setup, which were the modern optical detection systems based on microchannel and capillary electrophoresis. They were simple, cost effective, high sensitivity and good performance. Single basepair could be resolved and the limit of detection (LOD) of DNA sample pGEM-3Zf(+)/Hae III Markers was 2.4×10-11mol/L. which meet the requirement of DNA sequencing and short tandem repeat (STR) typing. The system could be divided in two parts: microchannel capillary electrophoresis and laser induced fluorescence detection.The electrophoresis section included the work as follows. The inner wall of the microchannel was modified to control the electroosmotic flow and restrain adsorption. The good performance sieving gel medium was prepared to separate the samples. The processes of coating, gel injection, sample injection and the flouorescece selection were optimized. The replacebale noncross-link linear polyacrylamide (LPA) was selected to be coating material and sieving medium. The electroosmotic flow mobility (EOF) of coated microchannel was 2.5165×10-8 m2 V-1 s1 which suited DNA separation. The characteristics of mobility were investigated and a new modified Ogston model was applied. The model was simple and suitable for the results of experiments. The electric field strength versus current curve was obtained. The signal intensity, band broading and resolution were analysed using different sizes of DNA fragment in different concentrations of sieving medium. The optimal concentration was 4%LPA.The detection section was designed of confocal optical path. Two systems were setup using 488nmAr+ laser and 532nm solid laser respectively. The laser excited the DNA fragments labeled dyes when they electrophoresed to the detection window. F fluorescence signals were collected by photomultiplier (PMT); the exciting and collecting optical system could be 3D adjusted. The design was optimized for maximum signal intensity by simulation and experiments. The size of focal spot in the micro-channel capillary was optimized. Fluorescence signal was enhanced 2～3 times when increasing the diameter of focal spot from 10μm to 50μm (full of the inner wall of capillary), through which the sensitivity and signal-noise ratio (SNR) were also improved. A technique of using refractive matching liquid was presented. The fluorescence signals were boosted up and the signal collection efficiency was also meliorated when using this method. The intensity and distribution of stray light in capillary any system were analysed by simulation and experiments. When the exciting beams illuminated at the center of capillaries, the stray light was strongest and was 2.7025 times of that without capillary. Stray light was compared for capillaries with different inner diameters; the optimum value was 50μm. The stray light of array with different spaces between capillaries was also researched. The results all above were useful for improving the signal collection efficiency, SNR and the mode selection of scanning.
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