Developmet Of Magnetic Particles For Purification DNA From Forensic Samples

It is well known that purification of DNA from forensic samples is a key technique in forensic DNA analysis. During the case investigation, trace material evidences which plays an important role in investigating case can be residue in crime scene, such as trace bloodstains, semen stain, exfoliated cells of fabric and so on. However, the DNA content of physical evidence is extremely low, and it is often influenced by the external environ-ment, which results in damage or degradation of the DNA molecule. Furthermore, the in-hibitors are always remained in the sample itself during the collection, all of these make it difficult to analyse the DNA of evidece. Thus, the high-quality DNA purification tech-nology is the premise to forensic DNA analysis successfully.Currently, the mainstream method of DNA purification includes Chelex-100, silicon membrane spin columns and so on, whose complicated operations, efficiency of purifica-tion, purity and integrity are correspondingly deficient, and depend on expensive kits of foreign companies highly.For sloving the problems above, this subject established an efficient, rapid and eco-nomical method for extraction of DNA from blood spots and hair follicle based on silica magnetic nanoparticles. According to the solid-purification principle, DNA is non-specifically binding on magnetic particles to form the complex of DNA and magnetic particle, which then be separated selectivity in the presence of an external magnetic field, so as to achieve the purpose of purification.The results show that,1) The method can purifiy DNA from blood spot steadily. The yield of DNA extracted by silica magnetic nanoparticles was about65ng in dry blood spot of5mm, good integrity that can be directly used for downstream of PCR reaction; the intra-batch CV (coefficient of variance) were7.93%-8.78%, and the inter-batch CV is10.1%, the results were ideal when comparing with commercial kits; For the common forensic samples such as trace bloodstains, buccal swab, cigarette butts and chewing gum for STRs genotyping, so have wide adaptability.2) Specially, we determined the composi-tion of lysis salts, the optimized concentrations of Ca2+and SDS to isolation of DNA from hair containing follicle. The yield of DNA extracted from three hair follicles by this opti-mized method was30-35ng with an A260/A280ratio of1.7-1.9; The results showed that the integrity of DNA is good by STRs multiplex PCR reaction. We can also purified the high-quality and complete mtDNA molecular.