Touch DNA in forensic science: a comprehensive overview and current status of the research

Touch DNA has become a pivotal tool in forensic science, enabling the identification of individuals from minute biological traces left on surfaces through physical contact. Despite its utility, challenges persist in understanding its composition, transfer mechanisms, and optimal recovery methods. This review provides a comprehensive overview of touch DNA, focusing on its origins, biological components, and the factors influencing its transfer and analysis in forensic investigations. A systematic literature review was conducted following PRISMA guidelines, analyzing 44 studies published between 2019 and 2025. Databases such as PubMed, Scopus, and Web of Science were searched using keywords like "touch DNA," "contact DNA," and "forensic DNA profiling." Eligible studies included original research articles detailing experimental models, sampling techniques, DNA extraction protocols, and amplification methods. Data were categorized and analyzed to identify trends and advancements in touch DNA research. The review highlights key findings, including the variability in DNA shedding among individuals ("good" vs. "poor" shedders), the impact of surface type (porous vs. non-porous), and environmental conditions on DNA persistence. Double swabbing emerged as the most effective sampling method, while the QIAamp DNA Investigator Kit and PowerPlex® Systems were widely used for extraction and amplification, respectively. Studies also revealed the significance of secondary DNA transfer and the potential of advanced techniques like direct PCR to enhance profiling efficiency. Touch DNA analysis has advanced significantly, yet challenges remain in standardization and interpretation. Future research should focus on refining recovery protocols, understanding transfer dynamics, and integrating novel technologies like transcriptome sequencing to improve forensic accuracy. This review underscores the need for interdisciplinary collaboration to address gaps and optimize touch DNA applications in criminal investigations.