Nanotechnology is the manipulation of matter on an atomic and molecular scale.
Nanotech was involved in the worst series of atrocities in known galactic history. Around 600 standard years ago, the Akaylan Empire was embroiled in all-out war with the Naxill Empire, another stellar nation. Both sides employed weaponized, self-replicating nanotech, which was a new technology at the time. The conflict spiraled out of control, with the Akaylans, unable to control their endlessly multiplying nanotech weapons, exterminating the Naxill from the Twin Spirals. The entire Naxill population of 3 trillion was wiped out, and a thousand planets were left as wastelands of nanotech grey goo. The Akaylans also suffered massive loses, estimated at around 35% of the nation’s populace, from which it took centuries to recover. Nanotech was soon outlawed by interstellar treaty.
Subsequently, nanotechnology (like antimatter), is taboo across the Twin Galaxies. Any facility attempting to create it is usually obliterated immediately by the closest galactic authority, though that doesn’t stop certain agencies from trying.