Isonucleic residue was a brown and sticky substance. (PIC: "Maps and Legends")
It could contaminate warp plasma, with concentrations of 20 parts per million being enough to label it far from pure. (VOY: "Fair Trade")
In 2385, the A500 android F8 did not understand a joke posed to him that asked "what's brown and sticky," and responded by listing substances including isonucleic residue. (PIC: "Maps and Legends")