Death particle
From Tardis Wiki, the free Doctor Who reference
The death particle was a particle that, when activated, was capable of destroying all organic life. The Cyberman Ashad held one in its chest and intended to use to wipe out organic life in the universe and evolve its race in full robots. Eventually, the Thirteenth Doctor indirectly used it to neutralise the Master powered by the Cyberium and its army of CyberMasters before they could leave Gallifrey and conquer the universe. (TV: The Timeless Children)
