Looks like it's from the fingernail clipping itself. They submerge the clipping in some solvent which cleans it of any contaminants, then they put the clipping in a different solvent which dissolves the clipping and releases the drug
analytes. From that point on the analysis is identical to hair drug testing.
I've posted a new discussion on this in the Forensic Drug Chemistry group
to initiate discussion and gathering of additional information. I'll be updating the Drug Testing Sticky
at some point with any information on these tests.
Any contributions or other information regarding any of these keratin drug tests would be greatly appreciated. There is still very little on the forums on this subject.