ferrous core-shell nanoparticles consisting of a magnetic γ-fe 2 o 3 multi-nanoparticle core and an outer silica shell have been synthesized and covalently functionalized with Rhodamine B (RhB) fluorescent molecules (γ-fe 2 o 3 /Sio 2 /RhB NPs). The resulting γ-fe 2 o 3 /Sio 2 /RhB nps were integrated with a renewable and naturally-abundant cellulose derivative (i.e. cellulose acetate, CA) that was processed in the form of electrospun fibers to yield multifunctional fluorescent fibrous nanocomposites. The encapsulation of the nanoparticles within the fibers and the covalent anchoring of the RhB fluorophore onto the nanoparticle surfaces prevented the fluorophore's leakage from the fibrous mat, enabling thus stable fluorescence-based operation of the developed materials. These materials were further evaluated as dual fluorescent sensors (i.e. ammonia gas and pH sensors), demonstrating consistent response for very high ammonia concentrations (up to 12000 ppm) and fast and linear response in both alkaline and acidic environments. The superparamagnetic nature of embedded nanoparticles provides means of electrospun fibers morphology control by magnetic field-assisted processes and additional means of electromagnetic-based manipulation making possible their use in a wide range of sensing applications. Nanoparticle-based systems containing more than one functional components represent an active research field having a great potential in numerous technological applications 1. Among others, magnetic core-shell nanoparticles offer new opportunities in the biomedical field, catalysis and sensing 2-10. In particular, fluorescent-functionalized silica-coated core-shell magnetic nanoparticles attract high attention in imaging and sensing applications. In such multifunctional nanomaterials the fluorescent dye can be covalently anchored either onto the silica surface or doped into the matrix of the silica shell 2,3,11-13. Electrospinning has been one of the most versatile methods employed for generating nano-and microfibers 14-16. Its simplicity, scalability and high versatility renders this method very attractive in many scientific fields. Electrospun polymer-based organic-inorganic fibrous nanocomposites have been developed by many research groups and further evaluated in various fields including biomedicine 17-19 , catalysis 20-22 , sensing 23 , energy 24,25 and environmental protection 26-29. However, only a few examples appear to date on the fabrication of nanocomposite electrospun fibers with embedded core-shell ferrous nanoparticles 30,31. In one such example, core-shell Fe/ FeO nanoparticles have been incorporated within polyimide fibers aiming to produce fibrous nanocomposites
Metal tips are emerging plasmonic structures that can offer high field intensity at the tip apex and high confinement in the nanoscale. The fabrication though of smooth metal tips with well-defined geometrical characteristics, crucial for optimizing the performance of the plasmonic structure, is not trivial. Furthermore pure metal tips are exposed to the environment and fragile, thus, complicating their use in real applications. The proposed platform based on hybrid composite glass metal microwires can offer the required robustness for device development. An optimized fabrication process of high quality all-fiber plasmonic tips by tapering such hybrid metal core/dielectric cladding microfibers is proposed and demonstrated experimentally. The presence of the dielectric cladding offers continuous re-excitation of the plasmon modes due to repeated total internal reflection at the glass/air interface which can dramatically reduce the high losses induced by the metal core. This enables direct light coupling from the distal end of fiber instead of side excitation of the tip, allowing thus their integration in optical fiber and planar circuits. Plasmonic tips were successfully demonstrated in a highly controllable manner and their performance was related to simulation results predicting high field enhancement factors up to 10 5 .
The fabrication of cost‐effective, polymer‐based electrospun fluorescent fibrous grids and their evaluation as candidates for sensing is reported, drawing useful results on their applicability and efficiency in gas sensing applications. A well‐defined, methacrylic homopolymer functionalized with anthracene moieties as fluorescent elements has been blended with a commercially available poly(methyl methacrylate) for the production of fluorescent electrospun polymer fibers. The formation of 3D grids can provide large interaction area with gas analytes and thus overcome quenching limitations induced by polymeric films, for more efficient sensing. These materials have been evaluated for ammonia sensing based on the fluorescence quenching of the anthracene fluorophores in the presence of ammonia vapors, exhibiting fast response at concentration up to 10 000 ppm. The covalent bonding of the anthracene fluorophore onto a hydrophobic polymethacrylate‐based backbone enables the future exploitation of the presented materials in sensing applications involving metal ions and biomolecules in aqueous media.
The development of plasmonic devices for sensing applications can offer high sensitivity and a dramatic improvement to the detection limits due to the high field enhancement at the metal surfaces. The platform proposed here is a tapered hybrid microfiber comprising a metal core and a glass cladding. The existence of a glass cladding not only serves as a mechanical host for the metal core, but also provides ease of handling regarding the tapering process. The advantages of this composite material system over pure metal tips are the absence of impurities and the multiple excitation of the plasmon modes due to the total internal reflection at the glass/air interface. The improved field enhancement at the apex of these tapered microwires was calculated through Finite Element Method (FEM) simulations. Enhancement factors up to 10 4 were theoretically observed for this type of tapered microwires. The use of different metals having different melting points and thermal expansion coefficients as well as different glass thicknesses can lead to an optimization of the tapering process conditions in order to achieve tapered microwires with the desirable geometrical characteristics.
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