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Mesoporous Silica-Templated Assembly of Luminescent Polyester Particles [1] Jiwei Cui, 1 2 * Yajun Wang, 1 2 Jingcheng Hao, 2 and Frank Caruso 1 * Presenter 1. Centre for Nanoscience and Nanotechnology, Department of Chemical and Biomolecular Engineering, The University of Melbourne, Parkville, Victoria 3010, Australia. 2. Key Laboratory of Colloid and Interface Chemistry of Ministry of Education, Shandong University, Jinan 250100, P. R. China. We report the template assembly of luminescent poly-3-hydroxybutyrate particles doped with rare-earth complexes. The hydrophobic polymer, poly-3-hydroxybutyrate, has been infiltrated into the nanopores of mesoporous silica particles in organic solvent. Owing to the van der Waals interaction of the polymer chains, poly-3-hydroxybutyrate loaded in the nanopores yields replicated particles following removal of the mesoporous silica template. To prevent aggregation of the hydrophobic poly-3-hydroxybutyrate particles in aqueous media, the poly-3-hydroxybutyrate-loaded mesoporous silica particles were coated with a polyelectrolyte multilayer shell through the layer-by-layer assembly of poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate). Following removal of the silica core, the polyelectrolyte multilayer-coated poly-3-hydroxybutyrate replicas were used to effectively coordinate rare-earth complexes (europium β-diketone complexes). The rare-earth-loaded poly-3-hydroxybutyrate replicas coated with polyelectrolyte multilayer emit intense luminescence over a wide range of pH (3~11) and for at least several months in aqueous solution, which is due to the intramolecular energy transfer from the ligand to the luminescent center in the rare-earth complexes. The poly-3-hydroxybutyrate replicas with stable and intense luminescence may find application in diagnostics and drug delivery. Introduction Mesoporous silica (MS) materials have attracted considerable attention in the areas of chemistry, physics, biology, and materials science since their introduction in the early 1990s. 1 Owing to their high surface areas (up to ~1200 m 2 g -1 ), unique pore structures (in the range of 2-50 nm), and tunable particle morphology, MSs have been widely used to load and encapsulate various species, and for the template synthesis of diverse nanostructured materials. 2-4 Replication of MSs with metals, 5 metal oxides, 6 carbon, 7 and polymers 8 have been achieved by filling the nanopores with small molecule precursors such as metal alkoxides, sucrose, and organic monomers, followed by hydrolysis, carbonization, or polymerization of the precursors and removal of the template. Recently, we introduced a method to prepare nanoporous, polymer-based spheres (NPS) by templating MS spheres. This approach involves infiltration of preformed macromolecules (i.e., polymers or proteins) into the nanopores of the MS particles, followed by crosslinking of the polymer chains, and removal of the MS particle templates. 9 The general applicability of this technique facilitates the design of polymeric particles with tunable properties by varying the macromolecules used, which can include synthetic polyelectrolytes, proteins, polypeptides, and polymer-drug conjugates. 10 Furthermore, this method permits tuning of the morphology and size of the nanoporous particles. Our previous studies have focused on infiltrating water-soluble macromolecules from aqueous solution to prepare particles that are dispersed in water. The preparation of similar but hydrophobic polymeric particles is also fundamentally interesting, as such particles can provide significantly different physicochemical properties to their hydrophilic counterparts. This may provide new opportunities for the loading and release of hydrophobic drugs, and for the protection and stabilization of molecules and macromolecules that are sensitive to aqueous [1]. Published at Chemistry of Materials (2009) 21:4310-4315
environments. However, challenges associated with preparing hydrophobic particles from hydrophobic constituents include a lack of control over the size of the particles and difficulties in dispersing them in aqueous media for water-based applications. In this work, we report a facile method to prepare hydrophobic poly-3-hydroxybutyrate (PHB) particles through templating MS spheres. PHB is hydrophobic polyester that has similar physical properties to those of polypropylene. Compared with previous reports, a significant difference of the current work is that no crosslinking of the infiltrated polymer chains is required to obtain intact replica particles, owing to the hydrophobic PHB chains, which can strongly associate and maintain the template particle morphology after MS template removal in aqueous solution. Furthermore, PHB is biocompatible and biodegradable, and has been evaluated as a material for use in tissue engineering scaffolds and controlled drug-release carriers. 11 Recently, it was reported that PHB can also be coordinated with rare-earth complexes to construct luminescent films. 12 We demonstrate that the obtained PHB replicas can be effectively used to coordinate rare-earth complexes. The rare-earth compounds (e.g., rare-earth β-diketone complexes) have unique spectral characteristics, including sharp emission peaks with a small peak width at half-height, long lifetimes, high fluorescence quantum yields, and a large Stokes shifts, 13 which makes them of interest in clinical diagnostic assays, genomic screening, and fluorescence immunoassays. 14 However, coordination of −OH groups significantly reduces the luminescence emission intensity and decay time of the rare-earth complexes because of nonradiative dissipation of energy of the high-energy −OH vibrations. 15 This has largely limited the application of rare-earth complexes in biology and related fields, in which aqueous media are typically required. Hence, the design of rare-earth materials with both strong luminescence and good stability in aqueous media is fundamentally important. 16 The rare-earth immobilized in the PHB replicas reported here can emit intense luminescence over a wide range of pH (3~11) and for at least several months in aqueous solution. The polyelectrolyte multilayer (PEM) coating (poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS)) on the PHB replicas provides stable and dispersed particles in aqueous solution. Experimental Section Materials. The MS particles with a bimodal pore structure (particle diameter, 2-4 μm; pore diameters, 2-3 nm and 10-40 nm) were synthesized via the protocol reported by Schulz-Ekloff et al. 17 Poly(allylamine hydrochloride) (PAH, M w 70 000), poly(sodium 4-styrenesulfonate) (PSS, M w 70 000), europium(III) chloride hexahydrate (EuCl 3·6H 2 O), 2-thenoyltrifluoroacetone (TTA), chloroform, and hydrofluoric acid (HF) were obtained from Sigma-Aldrich. Poly-3-hydroxybutyrate (M w 10 000) was purchased from Polysciences, Inc. The water used in all experiments was prepared in a three-stage Millipore Milli-Q Plus 185 purification system and had a resistivity greater than 18 MΩ·cm. Synthesis of the Rare-Earth Complex. The europium β-diketone complex, Eu(TTA) 3·2H 2 O (denoted as EuC), was synthesized according to published methods. 18 Briefly, 266 mg of TTA was dissolved in a solution of 6 mL ethanol and 1.2 mL of 1 M NaOH. Then, EuCl 3·6H 2 O (146 mg) in 42 mL of water was added to the above solution, and the mixture was heated at 60 ºC for 30 min. The yellow complex of EuC precipitated during cooling the solution to room temperature. The precipitate was dried in vacuum after removal of the solution through filtration and water washing. PHB Replicas from MS Particles, Surface Modification and EuC Loading. PHB was firstly loaded in the MS particles. Approximately 5 mg of MS particles were dispersed in 0.5 mL of the PHB solution (concentration of 35 mg mL -1 ) in chloroform at room temperature for 16 h. After removing the supernatant with centrifugation (1500 g for 2 min), the PHB-loaded MS particles were dried in a vacuum desiccator to remove the chloroform. The PHB-loaded MS particles were dispersed in water with brief sonication. After removing the supernatant with centrifugation (1000 g for 2 min), 500 μL of 2.5 M HF was added into the PHB-loaded MS particles. PHB replicas were obtained after three washing with water. PHB replicas coated with PAH/PSS were also prepared. Before removal of the MS templates, one PAH/PSS bilayer was coated on the PHB-loaded MS particles using the layer-bylayer (LbL) technique. 19 The PHB replicas coated with PAH/PSS multilayers were obtained after dissolving the silica particles. Details of this process are given in Figure 1. For the EuC loading, the PAH/PSS-coated PHB replicas were then dispersed in an ethanol solution of EuC for 16 h. After removal of the supernatant with centrifugation (2000 g for 2 min), three washings with water were carried out to remove the unadsorbed EuC. 81
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The 3 rd VACPS Research Workshop Pr
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Organizing Committee Victorian Asso
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Preface On the occasion of the publ
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Paper as a low-cost base material f
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Acknowledgements We gratefully ackn
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Career planning and Job Interview i
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The role of mitochondria in atrial
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Track-Before-Detect Procedures for
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Table 1. Correlations, Reliabilitie
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Early Childhood Education Matters:
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Noble, K. (2007). Parent choice of
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Supercontinuum generation for fiber
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Fiber Nonlinearity Precompensation
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