In English it's used with its literal Latin meaning: "in itself". So you might say "Well, his letter wasn't defamatory, per se." Inference: the words themselves didn't say anything defamatory, but the context in which they were interpreted might make them defamatory.
But (it seems to me) people sometimes seem to just tack "per se" on to any random noun in order to express vague doubt: "I'm saying this, but maybe I don't really mean it". "DNA per se" seems like a case in point: "DNA" is, as far as I can see, identical to "DNA in itself", in that DNA has no interpretive context that makes it become other than DNA. And on this occasion I can't even see why the writer wants to hedge her bets in this way.

Reminds me of an overheard remark in the hospital corridor: "And she's been told that they'll never be any use to her again. Not as feet."

Grant Hutchison