Neurotoxin

The Neurotoxin Production Facility's main storage tank

“

Do you hear that? That's the sound of the neurotoxin emitters emitting neurotoxin.

— GLaDOS'

”

Neurotoxin, comically referred to as Deadly Neurotoxin by GLaDOS, is a gaseous chemical agent that appears in Portal and in Portal 2's single-player campaign. Manufactured in the Neurotoxin Production Facility, neurotoxin can be ventiled into any part of Aperture Science Enrichment Center and is pumped through a series of emitters.

Overview

Neurotoxin is not an environmental hazard in the traditional sense of gameplay, as it only appears during specific, scripted events in the Portal series, mostly at the game's climax. In the Lab Rat comic, it is confirmed that GLaDOS ventilated neurotoxin as a means of killing all Aperture Science personnel prior to Chell's awakening in Portal, and is frequently used as an attempt to kill her. Later on in the single-player campaign of Portal 2, Wheatley also attempts to kill Chell with it.

The entirety of these gases are stored and manufactured in a reinforced tank, located in the bowels of the Enrichment Center. Eight main hoses allow the gas to be transferred to any location within the facility. During the chapter The Escape, Chell sabotages the system by cutting the eight primary hoses, thereby destroying the generator.

The variety of neurotoxin used within the Aperture Science facilty is unusual in that a certain concentration is required before it becomes lethal. Until the saturation level has been reached, the gas is not lethal and is presumed to be merely toxic. It is this delay that provides Chell with the opportunity to defeat GLaDOS in Portal and later, Wheatley in Portal 2.

Trivia

Despite the neurotoxin generator being completely destroyed by Chell and Wheatley early on in the game, Wheatley is still able to use neurotoxin in the final battle.
The Announcer is known to pronounce "neurotoxin" in two different ways: During the chapter The Escape and at the beginning of the final boss fight in "The Part Where He Kills You", he pronounces it as "ne-oo-rotoxin". However, later on in the same boss fight, he pronounces it way faster, as "nürotoxin"