Construction of Spherical Assembly of Gold Nanoparticles Using Tetra[(methylthio)methyl] silane as Ligand
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Construction of Spherical Assembly of Gold Nanoparticles Using Tetra[(methylthio)methyl]silane as Ligand Mathew M. Maye, I-Im S. Lim, Jin Luo, Li Han, Daniel Rabinovicha), Sandy Chen, Michael P. Maye and Chuan-Jian Zhong* Department of Chemistry, State University of New York at Binghamton, Binghamton, New York 13902; a) Department of Chemistry, The University of North Carolina at Charlotte, 9201 University City Boulevard, Charlotte, North Carolina 28223. ABSTRACT This paper reports a study on the assembly of gold nanoparticles via a tetradentate organosulfur ligand, tetra[(methylthio)methyl]silane. We have characterized the evolution of the assembly from individual nanoparticles to spheres (30 ~ 160 nm) of linked nanoparticles using UV-Visible, TEM, and AFM techniques. We have also demonstrated that the assemblies could be effectively disassembled via manipulating the ligand chemistry. Intriguing assembly-substrate interactions were observed, which could be related to interfacial hydrophobicity. Implications of these findings to the development of abilities in interfacial manipulation of the nanostructures are also discussed. INTRODUCTION The assembly of core-shell gold nanoparticles into functional thin films has a wide range of potential applications, including sensing, catalysis, drug delivery, microelectronics and medical diagnostics [1-2]. Many existing approaches have limited capabilities in manipulating the dimensionality of the assembly. While most synthetic approaches [3-4] explore the strong affinity of thiol groups to gold or silver surfaces, several recent reports involved the use of disulfides [5] or thioethers [6] as shell encapsulation. The thiolate-based chemistry is often exploited for nanoparticle assembly via crosslinking [7] such as stepwise assembling [8-10] and exchanging-crosslinking-precipitating [11]. The difference in metalbinding strength between thiols and thioethers, especially multidentate thioethers, may provide a new route for manipulating the dimensionality of the assembly and introduce chemical reversibility. In this report, we focus on the results of a study of the assembly of monolayer-capped gold “core-shell” nanoparticles (Aunm) using a tetradentate thioether, i.e., tetra[(methylthio)methyl]silane (Si(CH2SCH3)4, (TTE). The chemistry of this assembly explores the TTE-mediated binding and interparticle linking of gold nanocrystals towards spherical assembly. We note that similar morphology has been reported recently using molecular recognition structures on polymers to mediate the assembly of gold nanoparticles [12]. The structural, morphological, dimensional and reversible properties of the assembly were characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), and atomic force microscopy (AFM).
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EXPERIMENTAL Synthesis and Assembly: The core-shell nanoparticles utilized in this study were synthesized by the standard two-phased protocol [3] and were capped with monolayer shells of either tetraoctylammonium bromide (3.7 ±1.4 nm, TOA+Br--Aunm
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