Star Trek: 10 Huge Discoveries That No One Cared About
5. Nanoprobes
In the last few seasons of Voyager, Seven of Nine's Borg nanoprobes became the writer's favourite solution to pretty much any problem.
As mentioned earlier, they revived Neelix from the dead in the episode Mortal Coil and as we see from the episode Course: Oblivion, they can also improve warp capabilities (unfortunately, only a fake copy of the crew was able to figure this out right before dying). The list goes on and on. In the episode Friendship One, nanoprobes are used to heal radiation burns better than any medicine on the ship, and in the episode Someone To Watch Over Me they're used to cure an ambassador of his drunkenness by literally attacking the molecules of Synthehol in his bloodstream...
Unfortunately for all the crew of Voyager who died after Neelix, these methods are never used again.
While it is true that Seven of Nine possessed only a limited number of nanoprobes, Starfleet encounters numerous dead Borg drones and never thinks to salvage their nanoprobes even after Voyager learns of their powers.