9961
More importantly , it is shown that our NGO - PEG - PEI is able to deliver small interfering RNA ( siRNA ) into cells under the control of NIR light , resulting in obvious down - regulation of the target gene , Polo - like kinase 1 ( Plk1 ) , in the presence of laser irradiation .
 Chemical: PEG; Chemical: PEI
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: PEG; Chemical: PEI