Forensic trace DNA recovery and amplification from metal and metal-coated surfaces
Date
2022
Authors
Bonsu, Dan Nana Osei Amponsah Mensah
Editors
Advisors
Austin, Jeremy
Higgins, Denice
Higgins, Denice
Journal Title
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Thesis
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Abstract
Metals are problematic substrates of interest in frontline forensic practice due to difficulties
in obtaining probative DNA evidence from common metal objects and surfaces that are
routinely submitted for trace DNA analysis, such as cartridges, bullets, and casings. The low
success of trace DNA recovery from metal substrates has been linked to their
physicochemical nature, which can degrade DNA following deposition or act as inhibitory
contaminants that interfere with PCR amplification. However, the mechanisms behind metal-
DNA interactions and how this impacts the efficiency of trace DNA recovery and
downstream processes are poorly understood.
The research described in this thesis examined trace DNA samples recovered from metal and
metal-coated substrates in relation to typical forensic workflows from sample collection
through to short tandem repeat profiling. The studies aimed to identify and characterise the
negative effect of metal ions on DNA integrity, the collection and/or extraction of trace DNA
samples, the co-purification of inhibitory factors with DNA, the interference of metal ions
with quantitation, and how these ultimately impact DNA profiling.
Seven data chapters illustrate the importance of sampling techniques for the successful
recovery of trace DNA from metal substrates. The Isohelix™ swabbing system was shown to
be a more effective sampling tool than a Rayon swab. Depending on the chemistry of the
qPCR assay, the DNA template input, and the type and quantity of metal ions in the PCR
reaction, I observed non-patterned, complex interactions with unexpected DNA
quantification results. Additionally, metal ions in qPCR caused direct inhibition or secondary
interference of qPCR dye chemistry, leading to under and over-estimation of DNA
concentration. I also show that metal-mediated inhibition/degradation of cellular DNA is
matrix-dependent, paramagnetic DNA extraction may not be optimum for samples contaminated with ferrous metals, and co-purified metal inhibitors can lead to an imbalance
in STR profiles. When exposed to sunlight, self-cleaning metal-coated substrates, such as
those coated with titanium dioxide, promote the photocatalytic destruction of trace DNA.
Overall, this research highlights the importance of investigating novel trace DNA sampling
and quantitation strategies, as well as more sensitive and robust amplification methods, while
working with metal substrates.
School/Discipline
School of Biological Sciences
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 2022
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