title: Formation of Small Gold Nanoparticle Chains with High NIR Extinction through Bridging with Calcium Ions.
abstract: The self-assembly of citrate-capped Au nanoparticles (5 nm) resulted in branched nanochains by adding CaCl2 versus spherical nanoclusters for NaCl. These assemblies were formed between 1 s to 30 min by tuning the electrostatic repulsion and the interparticle bridging attraction between the cations and citrate ligands as a function of electrolyte concentration. For dilute Ca(2+), strong interparticle bridging favored particle attachment at chain ends. This resulted in the formation of small, branched chains with lengths as short as 20 nm, due to the large Debye length for the diffuse counterions. Furthermore, the bridging produced very small interparticle spacings and sintering, as evident in high-resolution TEM despite the low temperature. This morphology produced a large red shift in the surface plasmon resonance, as characterized by a broad extinction peak with NIR absorption out to 1000 nm, which is unusual for such small particles. Whereas these properties were seen for primary particles with partial citrate monolayers, the degrees of sintering and NIR extinction were small in the case of citrate multilayers. The ability to design the size and shape of nanoparticle clusters as well as the interparticle spacing by tuning bridging and electrostatic interactions may be expected to be quite general and of broad applicability in materials synthesis.
authors.affiliation: Texas Materials Institute, ‡McKetta Department of Chemical Engineering, and §Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Stover
authors.affiliation: Texas Materials Institute, ‡McKetta Department of Chemical Engineering, and §Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Moaseri
authors.affiliation: Texas Materials Institute, ‡McKetta Department of Chemical Engineering, and §Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Sai P
authors.initials: SP
authors.lastname: Gourisankar
authors.affiliation: Texas Materials Institute, ‡McKetta Department of Chemical Engineering, and §Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Iqbal
authors.affiliation: Texas Materials Institute, ‡McKetta Department of Chemical Engineering, and §Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Negin K
authors.initials: NK
authors.lastname: Rahbar
authors.affiliation: Texas Materials Institute, ‡McKetta Department of Chemical Engineering, and §Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Behzad
authors.initials: B
authors.lastname: Changalvaie
authors.affiliation: Texas Materials Institute, ‡McKetta Department of Chemical Engineering, and §Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Truskett
authors.affiliation: Texas Materials Institute, ‡McKetta Department of Chemical Engineering, and §Department of Chemistry, University of Texas at Austin , Austin, Texas 78712, United States.
authors.forename: Keith P
authors.initials: KP
authors.lastname: Johnston
mesh_terms: D002122:Calcium Chloride / Q000737:chemistry*; D002951:Citrates / Q000737:chemistry; D003102:Colloids; D006046:Gold / Q000737:chemistry*; D008027:Light; D053768:Metal Nanoparticles / Q000737:chemistry*; D054118:Nanospheres / Q000737:chemistry*; D010316:Particle Size; D012542:Scattering, Radiation; D012965:Sodium Chloride / Q000737:chemistry; D000077559:Sodium Citrate
chemical_list: D002951:Citrates; D003102:Colloids; D000077559:Sodium Citrate; D012965:Sodium Chloride; D006046:Gold; D002122:Calcium Chloride