The website of Mattel, the Barbie manufacturer, says Antoniadou joined Nasa in 2012 as a researcher.
However, Costas Bouyioukos, an assistant professor of bioinformatics at Paris Diderot University in France, says she has never worked at Nasa, and only completed the agency's Frontier Development Lab, an eight-week educational programme.
Greek Hoaxes, a team committed to debunking fake news, also doubted her claim to have worked on a team that built the first trachea implant to be successfully used on a patient at University College London.
The Nasa-Esa award does not appear to exist and Antoniadou's name does not appear on Nasa's record of award winners.
On Tuesday, she issued a statement on Facebook saying she was working on a project on artificial intelligence for Nasa. A spokesman for Nasa said she was not employed by the agency, but it could not rule out the possibility she had worked as a sub-contractor.