19470
Importantly , after being modified by tumor cell - specific targeting ligands ( e . g . , folate and RGD peptide ) , the PEGylated quaternary QDs show potential applications in tumor cell imaging as a promising alternative for Cd - based QDs .
 folate, Cd
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 folate, Cd