DNA transfer by examination tools--a risk for forensic casework?

Area of Science:

• Forensic Science
• Molecular Biology
• Genetics

Background:

• Increased DNA profiling sensitivity raises concerns about contamination in forensic casework.
• Tools used in exhibit examination pose a risk for transferring contaminating DNA.

Purpose of the Study:

• To assess DNA transfer risk from common forensic tools (scissors, forceps, gloves) between different substrates (cotton, glass).
• To investigate the impact of DNA transfer on target sample profiling and interpretation in forensic casework.

Main Methods:

• Simulated contamination by transferring dried blood and touch DNA using vectors between primary and secondary substrates.
• Varied contact levels (heavy/light) and substrate types (cotton/glass) to mimic real-world scenarios.
• Analyzed DNA transfer occurrence, level, and impact on target DNA profiling.

Main Results:

• All tested vectors transferred dried blood to cotton substrates; transfer was lower with glass substrates.
• Touch DNA transferred less efficiently than blood, with highest transfer between cotton and glass.
• Contaminating DNA detectability decreased with background DNA, but target profiles remained detectable, though interpretation was complicated.

Conclusions:

• Forensic tools can transfer DNA, posing a contamination risk, especially with cotton substrates.
• While target DNA profiles are usually interpretable, contamination complicates analysis and can affect evidence probative value.
• Strict adherence to laboratory cleaning protocols and minimizing item handling are crucial for contamination control.