Effects of time, high ambient temperature, swab type, and preservatives on forensic DNA recovery

DNA obtained from biological samples plays a significant role in both criminal and civil investigations. However, the probative value of DNA evidence is heavily influenced by the conditions under which the biological samples are collected, handled, and preserved, given their susceptibility to degradation over time. While general guidelines for handling different types of biological samples have been established by the government agencies and forensic laboratories, specific procedures for handling biological samples intended for forensic DNA analysis remain poorly defined in developing countries. As unforeseen delays between sample collection and DNA testing are common in forensic settings, factors such as traditional collection methods, inadequate air drying prior to packaging, and storage in evidence rooms lacking temperature control often result in laboratories receiving poor-quality samples, which further hinders the efficiency of forensic DNA analysis. In this study, we demonstrate the influence of collection method, storage medium and duration of storage under high ambient temperature on DNA recovery. Our results show that (a) nylon-flocked swabs facilitate improved DNA yields, (b) the use of DNA-stabilizing preservatives (commercially available or prepared in-house) increases the amplifiable DNA yield of samples stored at 35 °C for up to one month, (c) no amplifiable DNA was recovered from either type of swabs when stored dry at high ambient temperature for more than a week without a preservative, and (d) regardless of the swab material and the use of preservative, no amplifiable DNA could be extracted from samples stored up to two months at 35 °C. In sum, this work demonstrates that the use of nylon-flocked swabs together with DNA-stabilizing preservatives has a tangible impact on the amount of amplifiable DNA recovered from samples stored at high ambient temperature for up to a month, and that incorporating these methods hold considerable forensic utility.