jp036310w_si_001.pdf (70.05 kB)
Two-Step Functionalization of Neutral and Positively Charged Thiols onto Citrate-Stabilized Au Nanoparticles
journal contribution
posted on 2004-02-19, 00:00 authored by Shu-Yi Lin, Yi-Ting Tsai, Chien-Chih Chen, Chia-Mei Lin, Chun-hsien ChenWe propose a two-step approach to functionalize gold nanoparticles prepared by reducing tetrachloroauric
acid by trisodium citrate in water. The chloride and citrate physisorbed on the gold nanoparticles are first
displaced by thioctic acid (TA), which is then exchanged by thiols containing the desired functionality during
the second step. TA bears a carboxylate group and disulfide; at high pH, the negative charge of the former
stabilizes gold nanoparticles and the disulfide develops two S−Au bonds, retarding the desorption kinetics
upon further functionalization. The slow kinetics of TA desorption is crucial to establishing sufficient steric
stabilization for the gold core while losing electrostatic stabilization. Successful attachment of carboxylate,
crown ether, cyclodextrin, pyridine, and amino functionalities is verified by surface sensitive techniques. In
most cases, ca. 80% of the TA molecules are displaced. The nanoparticles are stable under solution pH where
the surface group is ionized. Although at certain solution acidities, the gold sols have difficulty carrying
charges and appear flocculated, the nanoparticles become dispersive after being centrifuged and redissolved
in suitable buffer solutions, which indicates the successful protection of the gold cores by steric stabilization.