2.4. DNA extraction methods for toenails
2.4.1. QIAGEN DNA investigator kit method
At least 0.01 g of toenail fragment(s) were weighed in a 1.5 mL
tube and 300 mL of Buffer ATL (Qiagen), 20 mL 20 mg/mL
Proteinase K (Qiagen) and 20 mL 1 M DTT (Sigma–Aldrich) added.
The tube was vortexed for 10 s and incubated with agitation for
0.5 h on a thermomixer (900 rpm) at 56 8C. The manufacturer’s
protocol ‘Isolation of Total DNA from Nail Clippings and Hair’ was
followed for the rest of the process using a manual extraction
method with carrier RNA included. Samples were eluted in 100 mL
of Buffer ATE (Qiagen). A pre-wash of the volunteer nail samples
was not required for the final developed method.
A number of modifications were applied to the optimised
method for the casework toenail sample extractions. The nail
was held with forceps while the surfaces of the nail were scraped
using a scalpel to remove material such as decomposed flesh and
dirt. The nail fragment(s) were rinsed in 1 mL of 70% (v/v)
ethanol (VWR International) solution vortexed for 30 s in a
1.5 mL tube. The solution was discarded and the wash repeated
using an additional 1 mL of 70% (v/v) ethanol solution. Nail
fragment(s) were left to dry for 5 min before being placed in a
new 1.5 mL tube for extraction. Toenail samples were extracted
following the manufacturer’s protocol ‘‘Isolation of DNA from
forensic casework samples’’ using a QIAcube for automation
(cases 5–30), or manually (cases 1–4) following the ‘Isolation of
Total DNA from Nail Clippings and Hair’ protocol as detailed above.