Fabrication and Characterization of Spectroscopically Encoded Core-shell Nanoparticle-polymer Nanocomposite
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Fabrication and Characterization of Spectroscopically Encoded Core-shell Nanoparticlepolymer Nanocomposite Sheng Dai, Abdiaziz Farah, Ramon A Alvarez-Puebla, Juan P Bravo-Vasquez, and Hicham Fenniri National Institute for Nanotechnology, 11421 Saskatchewan Drive, Edmonton, T6G 2M9, Canada ABSTRACT Metal nanoparticles are of great importance in the fabrication of new nanocomposite materials. One area of increasing interest is the application of metal nanoparticles (NP) as substrates for surface enhanced Raman scattering (SERS). In this regard, self-assembled monolayers (SAMs) of sulfur containing organic compounds are ideal target for SERS studies due to the strong affinity of sulfur for noble metals. Two types of molecules were synthesized for this study, an organic-soluble and a water-soluble styrene derivative. Self-assembling behaviors of these monomers on gold or silver nanostructured surfaces at room temperature were studied by UV-Vis spectroscopy, dynamic light scattering (DLS), SERS spectroscopy, and scanning electron microscopy (SEM). It was found that the interaction between sulfur compounds and metal NPs is strongly dependent on the NP size and the monomer environment. The hydrophilic NP surface switches to hydrophobic upon binding of sulfur-containing monomers, which leads to the formation of aggregates in aqueous solution for both water-soluble and oil-soluble monomers. The self-assembling behavior of these monomers on the metallic surface was compared with that of the corresponding homopolymers. Due to macromolecular and steric effects, the binding interaction between homopolymer and metal NP is weaker than that between NP and monomers. Surface polymerization of these monomers on metallic surfaces was observed as supported by SERS. Core-shell nanoparticles could also be obtained through seeded emulsion polymerization, but a decrease in SERS activity was observed.
INTRODUCTION Hybrid nanostructured materials composed of nanostructured metals and organic compounds have found increased interest in biological applications [1-3]. Self-assembled monolayer (SAM) formation is among the most popular methods to fabricate well-defined nanostructured hybrid materials and also to functionalize solid surfaces [4,5]. Noble metals, such as gold and silver, have strong binding affinity for sulfur containing organic compounds, which makes them ideal candidates for SAM-related studies. At the same time, the introduction of functionalized sulfurcontaining organic compounds onto the surface of these metallic surfaces offers the possibility to further modify the physical and chemical properties of such hybrid materials, leading to important applications in bioanalysis. Raman scattering has been widely used to study materials in bulk or in solution, although the Raman signal is generally weak. To overcome this limitation, surface enhanced Raman scattering (SERS), which results from a physical and chemical interaction between a nanostructured material and an analyte, was used for analyte detection at very low co
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