Death particle
From Tardis Wiki, the free Doctor Who reference
The Death Particle was a single particle created by the Cyberium, the shared artificial intelligence of the Cybermen, capable of wiping out all organic life on a planet. (TV: The Timeless Children)
Ashad, a half-converted Cyberman who absorbed the Cyberium, contained the Death Particle within the chest unit of his Cyber-suit. As the Cybermen were themselves part organic, they would be susceptible to this particle. Knowing this, they strove to make the final "ascension" to full mechanisation, removing their organic components and becoming completely mechanical, or "robots" as the Spy Master put it. (TV: The Timeless Children)
