Using single-cell elemental analytical methods at the Argonne National Laboratory in collaboration with inorganic chemist Tom O’Halloran, Woodruff discovered a role of zinc in the regulation of oocyte maturation and at the moment of fertilization. Using single-cell x-ray fluorescence, Woodruff and O’Halloran described the phenomenon of the "zinc spark," an event during which 10 billion zinc ions are lost from the egg. The discovery of the zinc spark was named as one of Discover magazine's top 100 stories of 2016.[3]