title: Equilibrium gold nanoclusters quenched with biodegradable polymers.
abstract: Although sub-100 nm nanoclusters of metal nanoparticles are of interest in many fields including biomedical imaging, sensors, and catalysis, it has been challenging to control their morphologies and chemical properties. Herein, a new concept is presented to assemble equilibrium Au nanoclusters of controlled size by tuning the colloidal interactions with a polymeric stabilizer, PLA(1k)-b-PEG(10k)-b-PLA(1k). The nanoclusters form upon mixing a dispersion of ~5 nm Au nanospheres with a polymer solution followed by partial solvent evaporation. A weakly adsorbed polymer quenches the equilibrium nanocluster size and provides steric stabilization. Nanocluster size is tuned from ~20 to ~40 nm by experimentally varying the final Au nanoparticle concentration and the polymer/Au ratio, along with the charge on the initial Au nanoparticle surface. Upon biodegradation of the quencher, the nanoclusters reversibly and fully dissociate to individual ~5 nm primary particles. Equilibrium cluster size is predicted semiquantitatively with a free energy model that balances short-ranged depletion and van der Waals attractions with longer-ranged electrostatic repulsion, as a function of the Au and polymer concentrations. The close spacings of the Au nanoparticles in the clusters produce strong NIR extinction over a broad range of wavelengths from 650 to 900 nm, which is of practical interest in biomedical imaging.
authors.affiliation: McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Avinash K
authors.initials: AK
authors.lastname: Murthy
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Stover
authors.forename: Ameya U
authors.initials: AU
authors.lastname: Borwankar
authors.forename: Golay D
authors.initials: GD
authors.lastname: Nie
authors.forename: Sai
authors.initials: S
authors.lastname: Gourisankar
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Truskett
authors.forename: Konstantin V
authors.initials: KV
authors.lastname: Sokolov
authors.forename: Keith P
authors.initials: KP
authors.lastname: Johnston
mesh_terms: D020341:Absorbable Implants; D003460:Crystallization / Q000379:methods*; D006046:Gold / Q000737:chemistry*; D008422:Materials Testing; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D011108:Polymers / Q000737:chemistry*
chemical_list: D011108:Polymers; D006046:Gold