I have no experience in medical work but learned in the service, that a nerve gas on a man’s skin, without inhalation, can quickly poison and kill him (if that’s of any assistance). Would it permeate hair and fingernails as with skin? I don’t know. Would it be present on hair and fingernails?
Typically, it is my understanding that nails are submitted as clippings or drillings and hair as clippings.. I do not think surface contamination is the source of toxin which is being tested for. If that was the case any body surface would suffice as a source for analysis.