Page 74 - Veritas - 02.03.22

• Substrate - Rough and porous surfaces like wood, concrete, and

grooved surfaces increase the friction between the skin and sur-

face, leading to greater amounts of touch DNA than smooth,

non-porous surfaces.

• Time of contact - Existing research on handling time and the

amount of DNA transferred during contact did not view signif-

icant variations among different handler times and the amount

of touch DNA extracted from surfaces.

How can touch DNA be collected?

The most commonly equipped technique to retrieve touch DNA

from surfaces is collection using sterile cotton swabs (wet/dry). How-

ever, this method has been found to cause significant sample loss

(~20 –76%) during extraction. Other methods include cutting out the

area for soft surfaces like garments. The most effective technique is

found to be tape lifting since it could extract DNA without signifi-

cant sample loss.

What are the possible limitations to using touch DNA as evidence?

• Though touch DNA can be recovered from surfaces like doorknobs,

multiple people come into physical contact with such surfaces lead-

ing to a mixture of DNA profiles. This would increase the workload

in the laboratory.

• Contamination by the personnel handling evidentiary items can-

not be overlooked when dealing with touch DNA.

• It has been found that DNA profiling from touch DNA samples on

improvised explosive devices (IEDs) post-detonation has poor suc-

cess rates.

• Evidence like fingerprints complicate the process of fingerprint

development as some development techniques hamper DNA re-

covery.

• Individuals need not always transfer DNA upon touching surfac-

es. Furthermore, touch DNA is capable of secondary transfer. For

instance, if a person uses a towel and the same is later used to wipe

a gun, there occurs an indirect transfer of touch DNA to the gun.

Thus, touch DNA can get transferred to a surface without direct

physical contact with the surface.