A comparative evaluation of forensic STR kits and their tolerance to PCR inhibitors

Abstract

ABSTRACT DNA samples used in forensic DNA analysis, especially casework evidence samples, are usually collected in diverse and harsh environments and often contain PCR inhibitors. DNA extracted from casework evidence samples is likely to have a low concentration. Additionally, the PCR clean-up process to remove PCR inhibitors can decrease DNA concentration. Therefore, through this study, we aimed to compare the inhibitor tolerance of short tandem repeat (STR) kits and identify their strengths and weaknesses in order to effectively apply and utilize the kits in forensic science. Inhibitor tolerance analysis of STR kits was conducted by measuring the peak height, limit of detection (LOD), and peak balance. The effect of the inhibitor on the peak height variation was determined using the effective concentration 50 (EC50) value. Inhibitor tolerance indicators, such as the LOD and peak balance of each kit, were measured in the presence of four inhibitors, including humic acid, haematin, calcium phosphate, and indigo carmine. No significant difference was observed for the inhibitors for each of the STR kits tested, with the exception of the Investigator® 24plex QS kit which had a significantly higher tolerance for calcium phosphate.