title: Quenched Assembly of NIR-Active Gold Nanoclusters Capped with Strongly Bound Ligands by Tuning Particle Charge via pH and Salinity.
abstract: Gold nanospheres coated with a binary monolayer of bound citrate and cysteine ligands were assembled into nanoclusters, in which the size and near-infrared (NIR) extinction were tuned by varying the pH and concentration of added NaCl. During full evaporation of an aqueous dispersion of 4.5 ± 1.8 nm Au primary particles, the nanoclusters were formed and quenched by the triblock copolymer polylactic acid (PLA)(1K)-b-poly(ethylene glycol) (PEG)(10K)-b-PLA(1K), which also provided steric stabilization. The short-ranged depletion and van der Waals attractive forces were balanced against longer ranged electrostatic repulsion to tune the nanocluster diameter and NIR extinction. Upon lowering the pH from 7 to 5 at a given salinity, the magnitude of the charge on the primary particles decreased, such that the weaker electrostatic repulsion increased the hydrodynamic diameter and, consequently, NIR extinction of the clusters. At a given pH, as the concentration of NaCl was increased, the NIR extinction decreased monotonically. Furthermore, the greater screening of the charges on the nanoclusters weakened the interactions with PLA(1K)-b-PEG(10K)-b-PLA(1K) and thus lowered the amount of adsorbed polymer on the nanocluster surface. The generalization of the concept of self-assembly of small NIR-active nanoclusters to include a strongly bound thiol and the manipulation of the morphologies and NIR extinction by variation of pH and salinity not only is of fundamental interest but also is important for optical biomedical imaging and therapy.
authors: Texas Materials Institute, McKetta Department of Chemical Engineering, and Department of Biomedical Engineering, University of Texas at Austin , Austin, Texas 78712, United States.
authors: Robert J
authors: RJ
authors: Stover
authors: Texas Materials Institute, McKetta Department of Chemical Engineering, and Department of Biomedical Engineering, University of Texas at Austin , Austin, Texas 78712, United States.
authors: Avinash K
authors: AK
authors: Murthy
authors: Texas Materials Institute, McKetta Department of Chemical Engineering, and Department of Biomedical Engineering, University of Texas at Austin , Austin, Texas 78712, United States.
authors: Golay D
authors: GD
authors: Nie
authors: Texas Materials Institute, McKetta Department of Chemical Engineering, and Department of Biomedical Engineering, University of Texas at Austin , Austin, Texas 78712, United States.
authors: Sai
authors: S
authors: Gourisankar
authors: Texas Materials Institute, McKetta Department of Chemical Engineering, and Department of Biomedical Engineering, University of Texas at Austin , Austin, Texas 78712, United States.
authors: Barton J
authors: BJ
authors: Dear
authors: Texas Materials Institute, McKetta Department of Chemical Engineering, and Department of Biomedical Engineering, University of Texas at Austin , Austin, Texas 78712, United States.
authors: Thomas M
authors: TM
authors: Truskett
authors: Texas Materials Institute, McKetta Department of Chemical Engineering, and Department of Biomedical Engineering, University of Texas at Austin , Austin, Texas 78712, United States ; Department of Imaging Physics, The UT M.D. Anderson Cancer Center , Houston, Texas 77030, United States.
authors: Konstantin V
authors: KV
authors: Sokolov
authors: Texas Materials Institute, McKetta Department of Chemical Engineering, and Department of Biomedical Engineering, University of Texas at Austin , Austin, Texas 78712, United States ; Texas Materials Institute, McKetta Department of Chemical Engineering, and Department of Biomedical Engineering, University of Texas at Austin , Austin, Texas 78712, United States.
authors: Keith P
authors: KP
authors: Johnston