Research on correlation between DNA typing and trace characteristics of blood after thermal exposure

The identification of biological evidence is particularly important for criminal detection, and the deoxyribonucleic acid (DNA) analysis plays a significant role in reconstructing events. However, bloodstains after thermal exposure in fires are quite unique compared to those in other scenes. Previous results regarding DNA recovery in bloodstains after heating are inconsistent with each other, which limits guidance for forensic science. In order to confirm the influence of heat on DNA recovery, the important physical evidence, bloodstain, was selected for its common occurrence, and a standard heat source, the Cone Calorimeter, was used to simulate high temperatures in fire scenes. A series of bloodstains were prepared under different heating conditions, and the results of short tandem repeat (STR) typing were systematically correlated with the trace characteristics of bloodstains. The findings indicate that heating bloodstains below 150 °C for less than 10 mins has minimal effect on DNA testing. After heating bloodstains at 150 °C for 20 mins or at 180 °C for 5 mins, partial DNA profiles were obtained, accompanied by blackening and cracking of the bloodstains. After exposure to 180 °C for 20 mins or 200 °C for 10 mins, no DNA profiles were obtained with bloodstains exhibiting metallic lusters and black bulges. Furthermore, from the perspective of chemical bond energy, the C-N, C-O, C-C, and P-O bonds in DNA molecules are prone to breaking during heating. The C-N bond serves as the primary connection between the four bases and the strand, while the C-O, C-C, and P-O bonds are significant connections within the DNA strand. It is thus hypothesized that the breakage of any bond aforementioned during heating results in the failure of DNA typing. Understanding the correlation between trace characteristics of bloodstains and DNA typing results after thermal exposure is crucial for comprehending DNA recovery from physical evidence collected from fire scenes.