pubs.acs.org/Langmuir © 2009 American Chemical Society
One-Step Synthesis of Phosphine-Stabilized Gold Nanoparticles Using the Mild Reducing Agent 9-BBN Patrick M. Shem, Rajesh Sardar,† and Jennifer S. Shumaker-Parry* Department of Chemistry, University of Utah, 315 South 1400 East, RM 2020, Salt Lake City, Utah 84112. Present address: Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599.
†
Received August 12, 2009. Revised Manuscript Received October 6, 2009 A simple method to synthesize phosphine-stabilized gold nanoparticles (AuNPs) of narrow size dispersion using the mild reducing agent 9-borabicyclo[3.3.1]nonane (9-BBN) is described. The methodology produces particles 1.2-2.8 nm in size depending on the reaction conditions and the phosphine ligand used. The phosphine-stabilized AuNPs exhibit size dependent localized surface plasmon resonance (LSPR) behavior as measured by UV-visible spectroscopy. 31 P NMR spectroscopy analysis of triphenylphosphine-AuNPs (TPP-AuNPs) shows a peak shift to 63.0 ppm compared to pure TPP at -5.4 ppm which is attributed to adsorption of TPP on the AuNP surface. Synthesis of trioctylphosphine-stabilized AuNPs demonstrates the versatility of the 9-BBN-based method. We present initial investigations of using TPP-AuNPs as precursor materials for nanoparticles functionalized with other ligands through ligand exchange reactions with dodecanethiol (DDT) and 11-mercaptoundecanoic acid (MUA).
Phosphine-stabilized gold nanoparticles (AuNPs) comprise an important class of nanomaterials finding broad application in areas such as nanoscale electronics development, catalysis, imaging, sensing, and new therapeutic approaches. For example, phosphine-stabilized AuNPs have served as effective catalysts for asymmetric organic transformations.1 In addition, these nanoparticles have been used as staining agents in biological imaging, immunoassays, and labeling of biological molecules such as proteins.2 In general, organic-ligand-stabilized metal clusters (∼2.0 nm) can serve as building blocks for two- or three-dimensional superlattices3 and in detection of organic and biological molecules.4 The structural5 and electronic properties6 of these clusters make them candidates for incorporation into nanoscale electronic and photonic devices.7,8 Phosphine-stabilized AuNPs *Corresponding author. E-mail:
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Langmuir 2009, 25(23), 13279–13283
may serve as the starting materials for production of nanoparticles functionalized by other ligands, such as thiols, amines, and other phosphines, in order to control material properties. For example, the use of a phosphine ligand as a stabilizer enables easy replacement by thiolated surfactants9 which may extend the solubility of the nanoparticles in aqueous media for nanobiotechnology4,10 and aqueous-based catalysis applications.11 For all of these applications, synthesis of small, uniform, stable nanoparticles is the initial challenge. Here we report a simple, one-step synthesis of phosphinestabilized AuNPs which produces high purity nanoparticles with narrow size dispersion and enables tuning of particle size. This synthesis is based on the mild reducing agent 9-borabicyclo[3.3.1]nonane (9-BBN). Recently, we showed that 9-BBN could be used to synthesize ω-functionalized alkylthiol- and azideterminated disulfide-stabilized AuNPs.12 The slow reduction by 9-BBN leads to good control over particle size and size dispersion. Here we demonstrate the versatility of the reducing agent 9-BBN to produce phosphine-stabilized AuNPs. We show that, by controlling the reaction conditions, AuNPs with diameters from 1.2 to 2.8 nm may be produced. In the literature, very few protocols are reported for synthesis of phosphine-stabilized AuNPs with average diameters of
