Quark inspects a vial of liquid data chains in 2370
A liquid data chain was a type of information device that came in liquid form.
In 2370, Quark helped the Klingon mercenary Yeto gain access to Deep Space 9 during a plasma storm in order to purchase a case of liquid data chains. The sale, however, was a ploy and the Klingon was actually part of a team hired by Verad to steal the Dax symbiont. Despite Quark's help, he was taken prisoner along with the rest of the station's senior staff. (DS9: "Invasive Procedures")
The script for "Invasive Procedures" describes Quark's liquid data chains as "...small vials of liquid [in] a padded case." [1]
The Star Trek Encyclopedia, 2nd ed., p. 274 describes them as a "fluidic information storage medium".