Touch DNA on Wood: Effects of Surface Morphology, Humidity, and Adaptive Recovery Strategies on Forensic DNA Yield

Authors: Ranjit B. Chahal and Salem K. Alketbi

DOI: 10.23880/ijfsc-16000453

Volume 11, Issue 1

Abstract

Wooden substrates are frequently encountered in forensic casework; however, their influence on touch DNA persistence and recovery remains comparatively underexplored relative to smooth non-porous materials and textiles. This study systematically evaluated the combined effects of surface morphology (smooth sealed versus rough unfinished wood), environmental exposure (room temperature [RT], low temperature/high humidity [LT], and high temperature [HT]), recovery strategy (swab, tape-lift, and sequential hybrid recovery), and time on DNA yield and STR profile quality. A total of 324 experimental samples were analysed under controlled conditions incorporating donor variability (low, moderate, and high shedders). Surface morphology exerted a significant effect on DNA yield (χ² = 18.7, df = 1, p < 0.001), with rough unfinished wood producing higher mean quantities than sealed surfaces. Environmental exposure significantly modulated persistence (χ² = 24.3, df = 2, p < 0.001), with HT conditions producing marked reductions in yield and RFU values (p < 0.01), whereas LT exposure resulted in moderated decline consistent with moisture-mediated redistribution rather than accelerated degradation. Recovery strategy demonstrated a significant main effect (χ² = 31.6, df = 2, p < 0.001) and surface-dependent interaction (p = 0.004). Tape-lift recovery outperformed swabbing on unfinished wood, while swabbing was generally sufficient for sealed surfaces. The hybrid strategy generated the highest cumulative yields; however, sequential fraction analysis revealed that the additive benefit was condition-dependent, with residual recoverable DNA most evident on unfinished wood under LT exposure. STR profile completeness and mean peak heights correlated with template quantity and environmental stress. RFU reduction preceded allelic dropout under HT conditions, while inhibition events were infrequent and did not materially influence profile outcomes. No interpretable mixtures were observed. Collectively, the findings demonstrate that wood exhibits dual forensic behavior—enhanced cellular retention coupled with environment-dependent recoverability. By integrating surface morphology, environmental modulation, and sequential hybrid fraction analysis, this study provides a substrate-informed framework for method selection and interpretation of touch DNA recovered from wooden exhibits in forensic casework.

Keywords: Forensic Genetics; Forensic Science; Touch DNA; Trace DNA; Wooden Substrates; Surface Morphology; DNA Persistence; DNA Recovery; STR Profiling; Environmental Exposure; Hybrid Sampling Strategy; Forensic Casework

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