reaction. The synthesized AuNPs were modified with 11-azido-1-undecanethiol as previously described. Briefly, 18 µl of 11-azido-1-undecanethiol (4.21 M) was added to 100 mL of citrate stabilized AuNPs solution in water with sonication. The color of the solution changed from red to violet indicating the modification of AuNPs with azidothiol. The violet solution was centrifuged for 10 min at 10000 rpm and the resulting precipitate was redissolved in DMF.