It is not clear what does "DNA with Au NP" stand for, therefore, it is difficult to guess the purpose to use NaCl. In general, physiological NaCl would just screen DNA charges at some extent and usage of the term "aging" is probably not correct in this case. 

Thank you, Ilko Bald, very much! Your answer really helped me!

Dear all

I would like to ask that the salt aging is using just for DNA functionalized gold nanoparticles or is there any reference which is used for another functionalization group?(like PEG)