20836
We report the design and synthesis of small - sized zwitterion - coated gadolinium - embedded iron oxide ( GdIO ) nanoparticles , which exhibit a strong T1 contrast effect for tumor imaging through enhanced permeation and retention effect and the ability to clear out of the body in living subjects .
 gadolinium, iron oxide, GdIO
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 gadolinium, iron oxide, GdIO