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A theoretical study of a cylindrical anisotropic optical fiber filled inhomogeneously by an anisotropic metamaterial is carried out. Nanoporous alumina microtubes obtained recently by acid anodization techniques are physical manifestations of such optical waveguides. In these microtubes, the nanopores are aligned radially outward and the nanopore diameters vary radially, rendering the system inhomogeneous. By considering the radial variation of the nanopore size, a local permittivity tensor is obtained by a Maxwell-Garnett homogenization theory. The cylindrically anisotropic and inhomogeneously filled fiber is shown to support propagating modes of hybrid polarization character (EH or HE modes). The salient feature of this system is that the modal fields are extremely confined near the center of the waveguide due to the refractive inhomogeneity. The anisotropy plays a relatively minor role in the localization. The easy control over the dielectric anisotropy and the inhomogeneity made possible in the nanoporous alumina fiber makes it an attractive candidate for nanophotonic applications.
We established a procedure to develop a localized surface plasmon resonance (LSPR) optical sensor platform for immunoassay. Computational simulations, focused on the assessment of the LSPR spectrum and spatial distribution of the electromagnetic field enhancement near the metallic nanoparticle, were used to engineer a nanostructured-sensing platform. Crucial parameters that rule the LSPR sensor performance, as bulk and molecular sensitivity, were evaluated, guiding the development of the optical platform. An LSPR surface-based platform composed of silver nanospheres adhered on a glass slide and functionalized with monoclonal anti-Candida antibodies of the IgG class was fabricated. Molecular biosensing was demonstrated by the identification of Candida albicans antigen. In particular, C. albicans is the most common species involved in a variety of hospital yeast infections. The developed sensing platform was able to identify C. albicans antigen concentration as low as 50 ng / mL, indicating the viability of exploring LSPR effect on C. albicans antigen biosensor. Moreover, this work provides insight on the LSPR behavior due to the adsorption of molecules layer on a nanoparticle surface, establishing a paradigm on engineering LSPR biosensor.
The functionalization of the nanoparticle’s (NP) surface is one method for tuning their overall properties to fit targeted applications. We developed a nanosensor based on the specific supramolecular interactions between ß-cyclodextrin (ßCD) nanocavities and organic molecules of biological interests using the metal-enhanced fluorescence effect (MEF) as the detection signal. We grafted ßCD, a typical macrocyclic host molecule that interacts specifically with different organic molecules and changes their physical properties (such as their fluorescence emission intensity), on gold NPs. To evaluate this nanosensor and the effect of the metallic core, we worked with a typical organic molecule, Rhodamine B (RhB), that has a strong association constant with ßCD (5700 M − 1) and is well-known to be quenched in the presence of cyclodextrins (CDs). The results show that, by grafting ßCD on gold NPs, it is possible to increase the sensitivity of RhB detection by 70%, 80%, and 294% when compared with solutions in (1) a phosphate buffer, (2) with ßCD, and (3) with Au NPs, respectively. These results show that the use of a supramolecular system attached to a metallic NP can interact specifically with a dye to enhance its fluorescence emission through the MEF effect. Moreover, this type of nanosystem can overcome the quenching of the signal by the matrix, such in the case of RhB with CDs. Eventually, this concept could be extended to other dyes with different quenching effects. For this reason, this type of nanosensor system could be used in the future to protect and enhance the dye emission of fluorophores in different biological media.
Deoxyribonucleic acid (DNA)-based functional materials containing luminescent molecules have attracted widespread attention as opto-electronic materials. In this study, luminescence properties of DNA/chiral Ru(phen)32 + complexes were investigated. The DNA/chiral Ru(phen)32 + complexes showed an enantioselective enhancement of luminescence. The DNA / Δ-Ru(phen)32 + complex showed a higher luminescence intensity and longer luminescence lifetime than the DNA / Λ-Ru(phen)32 + complex. Binding modes between DNA and Δ- / Λ-Ru(phen)32 + are discussed in terms of optical properties. The study shows that Δ-Ru(phen)32 + preferentially intercalates to form a more stable DNA complex than Λ-Ru(phen)32 + , leading to enantioselective luminescence enhancement.
Future low-voltage dielectric elastomer transducers (DETs), based on nanometer-thin elastomer membranes, will rely on soft and compliant electrodes with reasonable electrical conductivity and sound adhesion to the elastomer. State-of-the-art adhesion promoters, including nanometer-thin Cr/Ti films, result in defects for applied areal strains larger than 3% and lead to increases in the stiffness of DETs. To generate forces in the Newton range, these low-voltage DETs have to be stacked in thousands of layers. Herein, we present a compliant electrode, which consists of gold bonded covalently to thiol-functionalized polydimethylsiloxane (SH-PDMS) films. The membranes were fabricated using molecular beam deposition and in situ and/or subsequent ultraviolet light (UV) radiation. Peel-off tests demonstrate the expected strong binding of Au to the SH-PDMS network, with this highly stretchable Au/SH-PDMS layer capable of withstanding strains of at least 60%, without losing conductivity. Optical micrographs show signs of cracks for strained pure Au and Au/Cr electrodes but not for the Au/SH-PDMS layer. The mechanical properties and adhesion forces of Au/SH-PDMS were extracted by means of atomic force microscopy (AFM), using a spherical Au tip coated with methyl groups (CH3). The elastic modulus of ( 12 ± 9 ) MPa increased slightly against the 20-nm-thin Au/PDMS example, but it can be tailored by the cross-linking density of Au/SH-PDMS via the UV irradiation dose. Unloading nanoindentation curves revealed pull-off forces between the CH3-functionalized AFM tip and the Au/SH-PDMS layer at the time of separation. For Au/SH-PDMS, the spectral distribution of pull-off forces exhibits repulsive forces with the CH3 groups of the PDMS network as well as adhesive forces resulting from interactions with the nanometer-sized Au clusters. This approach provides the means to bind gold clusters homogenously within the SH-PDMS film. Such compliant electrodes are the prerequisite for fabricating low-voltage DETs that can be stretched by more than 50%.