Visualization and Recovery of Latent Cellular DNA Hair on Plastic Packaging Materials

Abstract

Latent DNA refers to undetectable traces of biological material deposited onto surfaces through direct contact. While previous forensic research has predominantly focused on latent DNA visualization from touched surfaces, fingerprints, and human hair, the transfer and persistence of latent cellular material deposited by animal and human hair onto commercial plastic packaging materials remains under-explored. In this study, hair samples obtained from domestic cat (Felis catus), dog (Canis lupus familiaris), and human (Homo sapiens) donors were stored in recyclable transparent plastic packaging bags for seven days under standardized friction conditions, alongside an empty plastic bag serving as a negative control. Visualization of latent DNA was achieved by applying SYBR Safe™ nucleic acid stain and inspecting the surfaces under a gel documentation system with blue (480 nm) and green (510 nm) light excitation. Biological material was recovered via swabbing, extracted using the QIAamp® DNA Mini Kit, and quantified using NanoDrop spectrophotometry. Fluorescence examination revealed a total of 80 distinct fluorescent cellular particles across all packaging surfaces, with blue light providing superior visual resolution (54 particles) compared to green light (26 particles). Cat hair packaging exhibited the highest fluorescence density (55%, n=44), followed by dog hair (26%, n=21) and human hair (19%, n=15), while the negative control displayed zero fluorescence. Extracted DNA concentration averaged 2.56 ± 0.95 ng/µL for human hair, 2.40 ± 0.78 ng/µL for cat hair, and 2.23 ± 0.67 ng/µL for dog hair, falling within target operational ranges for PCR amplification. Mean purity ratios (A260/A280) were highest in dog hair (2.31), followed by human hair (1.57) and cat hair (1.26). These findings prove that animal and human hair transfer recoverable latent DNA onto non-porous packaging, offering crucial investigative applications in combating illegal wildlife fur trade and solving violent human crimes involving plastic packaging.