Evaluation of current and novel methods for the storage of DNA-extracts

Dissertação de Erasmus Mundus para obtenção do grau de mestre em Técnicas Laboratoriais ForensesSecure preservation of DNA-extracts has been an issue at forensic laboratories for a long time. DNA-extracts are commonly stored at either -20°C or -80°C, but storage at these temperatures is not without risk of failure, environment unfriendly and costly. The Laboratório de Polícia Científica (LPC; Forensic Science Laboratory) of the Polícia Judiciária (PJ; Judicial Police) in Lisbon, Portugal is currently looking into new ways of storing their DNA-extracts at room temperature. Both DNAstable® and GenTegra-DNA®, two commercially available products for the storage of DNA-extracts at ambient temperatures, have been evaluated. DNA samples with extremely low concentrations of DNA (0.1 ng/μL, 0.05 ng/μL and 0.025 ng/μL) and DNA-extracts extracted from buccal swabs with the SwabSolution™ kit (Promega, Madison, USA) have been stored in standard polypropylene tubes, DNAstable® tubes and GenTegra-DNA® tubes for 8 days at four different conditions, i.e., -20°C, 4°C, at room temperature and at 60°C. Besides this, randomly selected DNA-extracts that have been stored at -20°C since 2006, 2009 or 2013 have been reanalyzed with the currently at the LPC used techniques in order to assess the level of degradation after long-term storage at -20°C. Results showed that DNA degrades over time at -20°C, with recovery levels found as low as 20% after three years of storage at -20°C. DNAstable® and GenTegra-DNA® both showed to be able to preserve DNA dried at room temperature and 60°C. Given the short period of storage full DNA-profiles have also been obtained from samples stored in standard polypropylene tubes at room temperature. Significant differences were found between DNA-extracts stored at 60°C with either DNAstable® or GenTegra-DNA® and those stored in unprotected tubes, showing that both DNAstable® and GenTegra-DNA® are capable of storing DNA at room temperature for long periods of time with a similar or even higher level of protection compared to those achieved with conventional storage at -20°C. Nevertheless, more research is needed before a switch can be made from frozen storage at -20°C to the storage of DNA-extracts at room temperature with products such as DNAstable® and GenTegra-DNA®