Infästning av celler på bomullstopsar och hur frisättningen av DNA kan underlättas

Abstract: A great number of cotton swabs from crime scenes are sent to the Swedish National Forensic Center each year for analyzation of DNA. Many of the swabs contain small amounts of cells and therefore it’s important to optimize the sampling of cells and the extraction of DNA. This would make more samples useful for DNA profiling and possibly be used as evidence. Today, a large amount of cotton, to where the cells adhere, is cut and used for extraction. To increase the concentration of DNA, the goal was to locate where the cells adhere to the swab and thereafter try to optimize the extraction of DNA. Different cutting techniques were used to cut the cotton to locate the area with the highest density of cells. These were then evaluated using quantitative PCR. Thereafter, different volumes of extraction buffer were used to try to minimize the volume needed for effective DNA extraction. Additionally, different microfuge tubes were used, and later different detergents were compared for a better extraction. Finally, cells were dyed with a fluorescent dye to be visualized in microscopes. In conclusion, both the results from the quantitative PCR and fluorescent microscopes showed that the cells are located on the top outside part of the cotton swab. Consequently, a smaller cotton piece could be cut and thereby a lower volume of extraction buffer was needed, thus resulting in a higher DNA concentration. Neither different microfuge tubes nor another detergent increased the concentration. However, it is recommended that an experiment with a large number of cotton swabs, from different origins, is performed to give a more statistically accurate picture of the performance in casework.