Publication date: 23/02/2023

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FLAVIA DE PAULA (M/D) Internal Examiner *

Summary: With the advancement of molecular biology techniques, contact DNA samples have become more explored and used in the field of forensic sciences. Among the existing contact samples, lip prints are sources of DNA and can be used in investigative contexts. This type of challenging sample can be found at crime scenes in beverage containers such as glasses, cans and bottles. In addition, the remaining liquids of these drinks are also considered potential sources of DNA and can be used in forensics. The aim of this study was to investigate the feasibility of obtaining DNA from contact samples from lip prints and beverages. In addition, it was verified whether variables such as temperature, humidity, exposure to sunlight and time influence the obtaining of this genetic material. During the experiment, 4 volunteers were asked to drink water, in a glass, and soda, in an aluminum can. Contact DNA samples deposited on the surfaces were collected 24 and 72 hours after their deposition. The collections were performed using swab. The remaining liquids in the containers were collected with the aid of a pasteur pipette. DNA was extracted through organic extraction and quantified by two different methodologies (Nanodrop and Qubit kit). According to the results, the quantification using the Qubit kit was more effective and specific when compared with the Nanodrop. It was not possible to detect correlation between temperature/humidity and the amount of recovered DNA. Direct exposure to sunlight was shown to have significant effects (p < 0.05), especially on samples deposited on aluminum surfaces. The results related to the time variable also indicated statistical differences (p < 0.05) when analyzed together with exposure to sunlight. Regarding liquids, the variables time and sunlight did not show a significant influence (p > 0.05) on the DNA yield obtained. From these results, it was found that it is possible to obtain DNA from contact samples from lip prints and drinks. In addition, it is noted that the yield of this type of sample can be significantly affected by environmental variables, mainly sunlight.

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