Superparamagnetic iron oxide nanoparticles can provide multiple benefits for biomedical applications in aqueous environments such as magnetic separation or magnetic resonance imaging. To increase the colloidal stability and allow subsequent reactions, the introduction of hydrophilic functional groups onto the particles’ surface is essential. During this process, the original coating is exchanged by preferably covalently bonded ligands such as trialkoxysilanes. The duration of the silane exchange reaction, which commonly takes more than 24 h, is an important drawback for this approach. In this paper, we present a novel method, which introduces ultrasonication as an energy source to dramatically accelerate this process, resulting in high-quality water-dispersible nanoparticles around 10 nm in size. To prove the generic character, different functional groups were introduced on the surface including polyethylene glycol chains, carboxylic acid, amine, and thiol groups. Their colloidal stability in various aqueous buffer solutions as well as human plasma and serum was investigated to allow implementation in biomedical and sensing applications.Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-012-1100-5) contains supplementary material, which is available to authorized users.
Magnetic (Fe3O4) and nonmagnetic (SiO2 and TiO2) nanoparticles were decorated on their surface with N-[(3-trimethoxysilyl)propyl]ethylenediamine triacetic acid (TMS-EDTA). The aim was to investigate the influence of the substrate on the behavior of these immobilized metal coordinating groups. The nanoparticles functionalized with TMS-EDTA were used for the adsorption and separation of trivalent rare-earth ions from aqueous solutions. The general adsorption capacity of the nanoparticles was very high (100 to 400 mg/g) due to their large surface area. The heavy rare-earth ions are known to have a higher affinity for the coordinating groups than the light rare-earth ions but an additional difference in selectivity was observed between the different nanoparticles. The separation of pairs of rare-earth ions was found to be dependent on the substrate, namely the density of EDTA groups on the surface. The observation that sterical hindrance (or crowding) of immobilized ligands influences the selectivity could provide a new tool for the fine-tuning of the coordination ability of traditional chelating ligands.
Spurred by research in magnetoplasmonics, plasmon-enhanced magneto-optical effects and active plasmonics, the demand for hybrid magnetic-plasmonic nanoparticle-based materials of optical quality is high. Currently used synthesis methods involve possibly interfering polymer media or polyelectrolyte interlayers, grooved supports or non-transparent substrates. To obtain homogeneous, partially transparent and polymer/polyelectrolyte-free magnetic-plasmonic nanocomposites with angle-independent optical properties, we produced hybrid gold-magnetite and silver-magnetite nanocomposites by a novel Layer-by-Layer synthesis using short bifunctional molecular linkers on glass substrates. Resulting nanocomposites had high nanoparticle filling fractions and showed tunability of the plasmon wavelength over a very broad spectral range by changing composite thickness through the number of added nanoparticle layers. The angle-independence of optical properties and the abilities to switch the plasmonic material and to tune the plasmon resonances of the magnetic-plasmonic composites make these materials a unique platform for magnetoplasmonic research.
Core-shell Fe 3 O 4 @SiO 2 nanoparticles were prepared with a modified Stöber method and functionalized with N- [(3-trimethoxysilyl)propyl]ethylenediamine triacetic acid (TMS-EDTA).The synthesis was optimized to make core-shell nanoparticles with homogeneous and thin SiO 2 shells (4.8 ± 0.5 nm) around highly superparamagnetic Fe 3 O 4 cores (14.5 ± 3.0 nm). The coreshell Fe 3 O 4 @SiO 2 (TMS-EDTA) nanoparticles were then used for the extraction and separation of rare-earth ions. By comparing them with previously published results for Fe 3 O 4 (TMS-EDTA) and SiO 2 (TMS-EDTA) nanoparticles, it was clear that the core-shell nanoparticles combine the advantage of magnetic retrieval observed for Fe 3 O 4 (TMS-EDTA) nanoparticles, with the higher selectivity observed for SiO 2 (TMS-EDTA). The advantages of the SiO 2 shell include a lower specific weight and a larger grafting density compared to Fe 3 O 4 surfaces, but also the improved resistance to acidic environments required for the stripping of rare-earth ions.
Ever since iron oxide nanoparticles have been recognized as promising scaffolds for biomedical applications, their surface functionalization has become even more important. We report the synthesis of a novel polyethylene glycol-based ligand that combines multiple advantageous properties for these applications. The ligand is covalently bound to the surface via a siloxane group, while its polyethylene glycol backbone significantly improves the colloidal stability of the particle in complex environments. End-capping the molecule with a carboxylic acid introduces a variety of coupling chemistry possibilities. In this study an antibody targeting plasminogen activator inhibitor-1 was coupled to the surface and its presence and binding activity was assessed by enzyme-linked immunosorbent assay and surface plasmon resonance experiments. The results indicate that the ligand has high potential towards biomedical applications where colloidal stability and advanced functionality is crucial.
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