Carolyn,

As far as I know, their use in -Pudd'nhead Wilson-  was the first
time fingerprints had been used in fiction to solve a crime and in a
trial to prove a point.  Certainly, in fictional chronology, because
PW is set before the War for Southern Independence, their use
in it precedes others.

I know of no prior appearance in American literature.

Do you know of an earlier use of electrified fences to kill than
that in -A Connecticut Yankee in King Arthur's Court-?  Or of
machine guns to shoot soldiers in trenches in the same novel?
While we're at it, aren't the first telephone in fiction, the first
long-distance phonecall, the first portable phone, the first
courtship by phone, the first overheard phone conversation, the
first phone scam, and the first wedding by phone in the short story,
"The Loves of Alonzo Fitz Clarence and Rosannah Ethelton"?

John H. Davis, Ph.D.
Chowan College