Evaluation of sampling and DNA extraction strategies for touch DNA recovery from plastic folder, wooden table, and plastic bag surfaces.

Skin cells (keratinocytes) and biological materials originating from sweat and sebum that are transferred to surfaces through physical contact are referred to in the forensic literature as touch DNA or trace DNA. Touch DNA plays a critical role in establishing the relationship between the perpetrator, object, and scene, particularly in cases where no visible biological traces are present. However, due to its typically low quantity, degraded nature, and high susceptibility to surface characteristics, the recovery of reliable DNA profiles from touch DNA remains challenging. Consequently, determining the most appropriate sampling method and DNA extraction strategy for different surface types constitutes a fundamental issue in forensic practice. In this study, the effects of two sampling methods (moistened microfiber swab and tape lifting) and two DNA extraction kits (QIAGEN QIAamp® DNA Investigator Kit and Thermo Fisher Scientific PrepFiler™ Forensic DNA Extraction Kit) on DNA recovery were comparatively evaluated across three commonly encountered forensic surface types: plastic folder, wooden table, and plastic bag. Samples were collected under sterile conditions from a total of 37 volunteers, and the recovered DNA quantities were quantitatively assessed. The results showed that DNA recovery was strongly influenced by the interaction between sampling method and extraction strategy. Across all surface types, the combination of tape lifting and the QIAamp® kit consistently yielded the highest median DNA recovery. In contrast, when the PrepFiler™ kit was used, the microfiber swab method resulted in higher DNA yields than tape lifting, although overall performance remained lower than that of the QIAamp®-tape lifting combination. A linear mixed-effects model confirmed a statistically significant effect of sampling-extraction method combinations on DNA yield (p < 0.001). In conclusion, the tape-lifting method combined with silica-based column extraction (QIAamp®) was identified as the most effective approach for recovering trace amounts of DNA from both non-porous and textured surfaces. These findings highlight the critical importance of optimizing the compatibility between surface type, sampling method, and DNA extraction kit in forensic DNA analyses.