Polymer-Encapsulated Gold-Nanoparticle Dimers: Facile Preparation and Catalytical Application in Guided Growth of Dimeric ZnO-Nanowires

Abstract

Rational assembly of nanoparticles is of vital importance for exploring fundamental electronic and optical properties and for constructing novel nanoscale devices. Through controlling aggregation kinetics, dimers and trimers of gold nanoparticles were generated and encapsulated with polymer by using a one-pot synthesis that involved simple heating and cooling. Dimers of gold nanoparticles were enriched from the resulting solution by centrifugation. The polymer shells maintain the stability of the nanoparticle organization, preventing aggregation and disintegration during subsequent purification, enrichment, and application. A typical enriched sample showed that the dimer population reached 61% among 989 nanoparticles surveyed. In a proof-of-concept application, the gold nanoparticle dimers were used as catalyst to guide the growth of dimeric zinc oxide nanowires. Nanowire dimers with unprecedented narrow spacing (20 to 60 nm) were achieved using a vapor transport growth method; dimeric nanowire population reached approximately 25%.

A systems approach towards the stoichiometry-controlled hetero-assembly of nanoparticles

“…2b-e), which basically involved the functionalization of the B-NP surface by a hydrophobic ligand (2, Fig. 1b), followed by PSPAA self-assembly 6,25,26 . Ligand 2 cannot replace the hydrophilic ligand 1 on the surface of A-NPs, which was thus not encapsulated.…”

“…The key challenge is to develop general methodologies to assemble colloidal nano-objects with precise stoichiometry. Previously, homo-aggregates such as dimers and trimers were prepared by exploiting either random aggregation [6][7][8] , steric effects [9][10][11][12] or specific control over surface ligands (for example, divalent NPs) [13][14][15][16] . Compared with these 'homo-coupling' nanoreactions, controlling stoichiometry in the 'cross-coupling' of NPs presents different and arguably greater challenges.…”

“…We have recently demonstrated that encapsulation of nanoclusters in polystyrene-block-poly(acrylic acid) (PSPAA) micelles is a way to overcome these problems and affords sufficient stability for the nanoclusters to be separated using concentrated CsCl solutions 6,23,24 .…”

Covalently linked multimers of gold nanoclusters Au102(p-MBA)44and Au∼250(p-MBA)n

“…The most straightforward is to simply aggregate NPs. 8 More stable structures can be achieved with polymer or silica encasing 9,10 or templating polymer layers 11 . Lithography has been extensively used to fabricate plasmonic nanoparticle assemblies in a controlled way.…”

Rational design and synthesis of SERS labels

“…Alivisatos and co-workers and Mirkin and co-workers have demonstrated the assembly of AuNPs into dimers, trimers and larger clusters based on a DNAprogrammed procedure. 63,64 Chemical linkers such as rigid, multivalent thiol-linkers, 65 phenylacetylene, 66,67 thiol-terminated hydrophobic ligands 68 and diamines 69,70 have been demonstrated for the fabrication of dimers with a relatively high yield. To be used for efficient SERS, Xia and co-workers proposed a simple and one-step method that generates dimers without any additional assembly steps by introducing a small amount of sodium chloride into the reaction medium.…”