Novel Ferromagnetic Aerogel Composite Materials with Nanoparticles Formation and Chemistry in Response to Light
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Novel Ferromagnetic Aerogel Composite Materials with Nanoparticles Formation and Chemistry in Response to Light Chunhua Yao, Xipeng Liu and William M. Risen, Jr. Department of Chemistry, Brown University Providence, RI 02912, U.S.A ABSTRACT Smart composites based on ferromagnetic hybrid aerogels have been prepared. These novel materials change chemistry in response to light to form nanoparticles that react with compounds that are present in the environment of the aerogels. Thus, high surface area silica/functional polymer hybrid aerogels have been formed via sol-gel synthesis. They also can contain coordinated metal-ion species. They are reacted with Fe-precursors to form air stable ferromagnetic aerogels, which they are transformed into active particles themselves or by incorporation of additional metal ions. These active materials, which adhere to tissue, can be positioned magnetically within their environment. Once they are positioned, they can be transformed by UV light to form Au(0) nanoparticles which react with the molecules in their environment. The preparation and properties of these aerogels, their photochemistry and reaction with bio-molecules will be presented. INTRODUCTION Magnetic separation has become an effective way to achieve biomolecular separation since its discovery by Robinson et al. [1]. The basic procedure comprises selective binding of biomaterials of interest to magnetically active materials and separation from the surroundings using an external magnetic field [1]. Magnetic nanoparticles of iron, magnetite, and maghemite have remarkable properties, including ferromagnetism and superparamagnetism with high saturation fields. However, such nanoparticles need to be hosted or coated by nonmagnetic materials to avoid aggregation and sedimentation to be applied usefully. Coating the magnetic particles with silica is one common and important approach [2-5]. In order to be useful for bio-separation, the surface of the silica needs to be functionalized. For example, S. Giri et al [6] reported the possible stimuli-responsive controlled-release delivery based on amine group functionalized mesoporous silica magnetic nanoparticles composites. We have shown that aerogels based on silica and a bio-derived polymer, especially chitosan-silica (X-SiO2), can be produced with high porosity and BET surface areas in the 400-1100m2/g range with amine functionality that is both accessible and active in the material. Further, they can be synthesized with metals ions such as Au(III) coordinated to the chitosan, and that they can be photo-reduced to produce distinct separated Au (0) nanoparticles distributed in the aerogel matrix. These Au nanoparticles react with a range of biotinylated, thiolated and other bio-molecules, such as cystamine to introduce the bio-active functionality to the aerogel composites [7]. Separately, we have shown that by gas-infusion and thermal decomposition, we can grow ferromagnetic nanoparticles such as Fe, into an aerogel matrix without affecting gold nanoparticles’ chemic
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