21220
TSS - SPIONs demonstrated an iron oxide core diameter ( crystallite size by XRD ) of 3 . 1 +/- 0 . 02nm , a hydrodynamic diameter of 94 +/- 20nm , a zeta potential of + 21 +/- 5mV , and an iron content of 3 . 6 +/- 0 . 9mg / mL .
 Chemical: iron oxide; Chemical: iron
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: iron oxide; Chemical: iron