Chroniton

Chronitons are subatomic particles with temporal properties. Although not harmful to humanoids, chronitons can be fatal to lifeforms which exist outside of time, such as the beings known to the Bajorans as "Prophets," and their mortal enemies, the Pah-wraiths. 

Chronitons were produced by the normal operation of Romulan cloaking devices, and were often associated with the phenomenon of time travel. The Orb of Time was known to produce a surge of chronitons when in operation. The temporal transporter utilized by the crew of the 29th century timeship Relativity produced a detectable chroniton flux of .003. 

The Borg utilized chroniton fields, projected throughout a Borg vessel via specially-designed conduits, to compensate for the extreme temporal stress of a transwarp conduit. 

Overview
In 2368, Lieutenant Commander Geordi La Forge and Ensign Ro Laren became "phased" due to exposure to chroniton particles being emitted from the cloaking device of a Romulan science vessel which the Enterprise was assisting. As the Romulans had attempted to produce an interphase generator by combining their cloaking device with a molecular phase inverter, this had the effect of altering La Forge and Ro's molecular structure, making it impossible for them to interact with anything but each other. 

In 2371, the chronitons produced by the USS Defiant (2370)'s cloaking device, which had lodged in the ship's ablative armor matrix, shifted into a high state of temporal polarization due to a temporal surge from an exploding microscopic singularity passing through the Sol system. This caused a transporter beam passing through the polarized particles carrying Captain Benjamin Sisko, Lieutenant Jadzia Dax, and Doctor Julian Bashir, to be redirected through time, resulting in their materializing in San Francisco, the year 2024. Chief O'Brien and Major Kira were later able to use the remaining polarized chronitons to mount a rescue mission for their stranded crewmates. 

In 2373, a Pah-wraith inhabiting Chief O'Brien's wife Keiko forced Miles to perform a series of modifications to Deep Space 9's deflector grid, transforming the station into a massive chroniton array aimed directly at the Bajoran wormhole, where the temporal disruption would kill all of the Prophets. O'Brien was able to successfully complete the modifications, but instead of aiming the chroniton beam at the wormhole, he targeted the runabout which he and Keiko were aboard, driving the Pah-wraith out of Keiko's body. A year later, Kai Winn utilized a chroniton generator to drive out a Prophet and a Pah-Wraith who had inhabited the bodies of Major Kira and Jake Sisko, respectively. Although Captain Sisko insisted that the battle between the two, called "the Reckoning" in Bajoran mythology, be allowed to play out, Winn covertly activated the generator in an attempt to subvert Captain Sisko's role in Bajoran affairs. 

The Delta Quadrant species the Krenim utilized chroniton-based torpedoes as weapons, which had the ability to pass through an enemy's shields due to being in a constant state of temporal flux. In an alternate timeline in 2374, Kes was exposed to chroniton radiation from a torpedo fragment. Although she was inoculated against the radiation poisoning, five years later the dormant chronitons in her cells would be reactivated by exposure to a biotemporal field. This shifted her cells into a state of biotemporal flux, causing her to experience a series of backward time jumps, essentially living her life in reverse. The time jumps were halted in 2373 when The Doctor was able to expose her to a precisely modulated field of antichronitons, purging her system of the chronitons. 

In 2374, when Molly O'Brien fell through a time portal on the Bajoran colony world of Golana, Lieutenant Commander Dax and Molly's father, Miles O'Brien, were able to determine that Molly had been sent approximately three hundred years into the past by analyzing the chroniton signature. 

In 2377, Voyager encountered a spatial rift emitting high levels of neutrinos and chronitons. When a chronokinetic surge struck the ship, it was fractured into thirty-seven different time periods. The Doctor subsequently created a chroniton-infused serum to treat Commander Chakotay, whose body was in a state of temporal flux as a result of the surge. The serum allowed Chakotay to pass through the barriers separating the time periods, and recruit Captain Janeway's counterpart from 2371, injecting her with the same serum. Chakotay and Janeway then started distributing the serum throughout the ship, using the bio-neural circuitry, and then used the gel packs to transmit a chroniton field, generated by Voyager's warp core. The plan was successful, and Voyager was brought back into temporal synch to a time period mere moments before the chronokinetic surge struck the ship. With only seconds, Chakotay rerouted power to the main deflector and reset its polarity, using it as a lightning rod to absorb the surge, averting the accident.