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.
Original language | English (US) |
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Pages (from-to) | 239-251 |
Number of pages | 13 |
Journal | ACS Nano |
Volume | 7 |
Issue number | 1 |
DOIs | |
State | Published - Jan 22 2013 |
Keywords
- biodegradable nanoparticles
- colloidal forces
- depletion attraction
- equilibrium assembly
- nanoclusters
- plasmonic nanoparticles
ASJC Scopus subject areas
- General Materials Science
- General Engineering
- General Physics and Astronomy