TY - JOUR
T1 - From discrete particles to spherical aggregates
T2 - A simple approach to the self-assembly of Au colloids
AU - Zhong, Ziyi
AU - Subramanian, Alamelu Suriya
AU - Highfield, James
AU - Carpenter, Keith
AU - Gedanken, Aharon
PY - 2005/2/18
Y1 - 2005/2/18
N2 - Here we demonstrate a simple, template-free approach to the formation of spherical gold aggregates through the reduction of HAuCl4 by NaBH4, in the presence of cysteine (Cys) as a capping agent. The resulting aggregates are quite stable in solution. The pH of the solution and the molar ratio of Au:Cys are two key empirical factors in the formation of such highly ordered aggregates. At slightly alkaline pH (7-10) and with Au:Cys ratios ranging from 1:0.5 to 1:2, spherical Au aggregates of 30-80 nm are formed. At lower Cys ratios (Au:Cys ≥ 1:0.5) very loosely linked aggregates are formed; however, at very high Cys ratios (Au:Cys ≤ 1:3), highly dispersed Au particles of 2-4 nm are obtained, which are virtually indistinguishable from the original colloidal form. Aggregate size is influenced markedly by component concentration; a 3-fold increase in standard levels resulted in Au spherical aggregates of a larger size, 200-500 nm. In addition, we used a combination of Cys and lysine (Lys) as a capping agent/cross-linker and found that the morphology of the Au colloid aggregates can be easily manipulated from a linear to a spherical form by adjusting the proportions of Cys and Lys in the capping agent/cross-linker mixture. The introduction of mercapto (SH)-containing organic acids reduced the cross-linking ability of Cys, especially in the case of long-chain acids. Complete disruption of the spherical aggregates highlights the importance of Cys per se. An explanation of this ordered self-assembly process is proposed, in the context of the known surface chemistry of Au colloids.
AB - Here we demonstrate a simple, template-free approach to the formation of spherical gold aggregates through the reduction of HAuCl4 by NaBH4, in the presence of cysteine (Cys) as a capping agent. The resulting aggregates are quite stable in solution. The pH of the solution and the molar ratio of Au:Cys are two key empirical factors in the formation of such highly ordered aggregates. At slightly alkaline pH (7-10) and with Au:Cys ratios ranging from 1:0.5 to 1:2, spherical Au aggregates of 30-80 nm are formed. At lower Cys ratios (Au:Cys ≥ 1:0.5) very loosely linked aggregates are formed; however, at very high Cys ratios (Au:Cys ≤ 1:3), highly dispersed Au particles of 2-4 nm are obtained, which are virtually indistinguishable from the original colloidal form. Aggregate size is influenced markedly by component concentration; a 3-fold increase in standard levels resulted in Au spherical aggregates of a larger size, 200-500 nm. In addition, we used a combination of Cys and lysine (Lys) as a capping agent/cross-linker and found that the morphology of the Au colloid aggregates can be easily manipulated from a linear to a spherical form by adjusting the proportions of Cys and Lys in the capping agent/cross-linker mixture. The introduction of mercapto (SH)-containing organic acids reduced the cross-linking ability of Cys, especially in the case of long-chain acids. Complete disruption of the spherical aggregates highlights the importance of Cys per se. An explanation of this ordered self-assembly process is proposed, in the context of the known surface chemistry of Au colloids.
KW - Aggregation
KW - Colloids
KW - Gold
KW - Self-assembly
KW - Surface charge
UR - http://www.scopus.com/inward/record.url?scp=14844292636&partnerID=8YFLogxK
U2 - 10.1002/chem.200400529
DO - 10.1002/chem.200400529
M3 - 文章
C2 - 15657964
AN - SCOPUS:14844292636
SN - 0947-6539
VL - 11
SP - 1473
EP - 1478
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
IS - 5
ER -