A Kinetic Study of Mediator-Template Assembly of Gold Nanoparticles
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A Kinetic Study of Mediator-Template Assembly of Gold Nanoparticles I-Im Stephanie Lim, Wui Ip, Alice Pak, Jin Luo, and Chuan-Jian Zhong* Department of Chemistry, State University of New York at Binghamton, Binghamton, New York 13902, USA. * [email protected]
ABSTRACT This paper describes a kinetic study of the mediator-template assembly of gold nanoparticles in solutions based on the spectrophotometric measurement of the surface plasmon resonance optical property. Gold nanoparticles of ~5 nm diameter encapsulated with tetraoctylammonium bromide shells were studied as a model system. The core-shell nanoparticles were assembled into 3D spherical assemblies via a mediator-template assembly route in which a thioether-based multidentate ligand functions as a mediator and the tetraoctylammonium shell molecules function as a templating agent. In this report, the results were compared with those obtained for the assembly of gold nanoparticles in several different systems with features similar to the mediator-template assembly. The findings further provided further insights into understanding the kinetic factors governing the assembly of nanoparticles, and have important implications to the design and control of the nanostructures for sensory and catalytic applications.
INTRODUCTION The interests in studying nanostructures are largely driven by the recognition of the unique optical, electronic, catalytic and magnetic properties of the materials at the nanoscale level. In order to fully exploit the nanoscale properties, the ability to synthesize and assemble nanoparticles with controllable sizes, shapes and interparticle properties is essential. Among the many strategies to encapsulate and stabilize the metal or semiconductor nanoparticles [1], different approaches has been established, including layer-by-layer stepwise assembly [2], molecularly-mediated exchange-crosslinkingprecipitation assembly [3], DNA-linked assembly [4], polymer-mediated assembly [5], and multidentate thioether assembly [6]. The encapsulation of nanocrystal cores with an organic monolayer has been proven very effective because the monolayer shell not only acts as a protective shell, resisting the propensity of aggregation, but also be fine-tunable to achieve the desired interfacial chemistry in controllable ways. This approach is useful for the synthesis of nanoparticles with desired sizes, shapes, and surface properties. Potential applications for nanoparticle assemblies include chemical sensing [7], catalysis [8], drug delivery, microelectronics [9], and medical diagnostics [10]. We have recently reported a mediator-template assembly route for the assembly of gold nanoparticles using a multidentate thioether (e.g., methyltris[(methylthio)methyl]silane (MeSi(CH2SCH3)3), (TE3)) as the mediator and a surfactant (e.g., tetraoctylammonium bromide, [CH3(CH2)7]4N+ Br-, (TOA+Br-)) as the template [6]. The TE3-mediated and TOA-templated interparticle linking of gold nanoparticles has been
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shown to lead to the assembly of
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