Nanofabrication of nanostructured metal–insulator–metal metamaterial (NMIM ² ) by the electron beam lithography and the liftoff technique is reported in this paper. The NMIM ² consists of periodic arrays of gold (Au) nanotriangles deposited on a gold layer (acting as a mirror) separated by a thin dielectric insulator. Such an NMIM ² stack was fabricated on a silicon wafer. Reflection of the NMIM ² was measured by the Fourier transform infrared spectroscope. The experimental measurement for reflection coefficients are in good agreement with the full-wave finite-different time-domain simulation results. At resonance, we numerically observed a strong field localized inside the gap between the Au nanostructures and the Au mirror, resulting in a strong confinement of incoming light within the insulator spacer and, thus, a pronounced absorption at telecommunication wavelengths. This resonant spectral response is investigated for sensitive label-free refractive index biosensing applications.

We investigate properties of nonlinear resonant gratings with emphasis on optical bistability. Slab waveguide gratings with various quality factors are designed and their characteristics analyzed with a finite-difference time-domain method. Considerable field enhancements are observed in the gratings and the performance compares favorably with metallic bistable devices. Bistabilitiy based on coupled gratings is also treated. Mechanically controllable switching intensity realized by varying a gap distance between two gratings is demonstrated. Resonant nonlinear elements in this work may find applications in all-optical information processing and optical switching, and our investigation on the dependence of the normalized switching intensity and the response time on quality factor will provide a general guide line for grating-based bistable device design.

We presented synthesis and physical characterization of iron oxide magnetic nanoparticles (Fe₃O₄) for biomedical applications in the size range of 10-30 nm. Magnetic nanoparticles were synthesized by the coprecipitation method, and the particles’ size was controlled by two different injection methods of sodium hydroxide (NaOH). The synthesized magnetic nanoparticles were then modified by using series of linkers including tetraethyl orthosilicate (TEOS), 3-aminopropyltriethoxysilane (APTES), and glutaraldehyde (GA) to generate the structure of Fe₃O₄/SiO₂/NH₂/CHO, which can be used for immobilization of protein A. Additionally, we used transmission electron microscopy (TEM), X-ray powder diffraction (XRD), vibrating-sample magnetometry (VSM), and Fourier-transform infrared spectroscopy (FTIR), for characterization of properties and structure of the nanoparticles. An immobilization of protein A on magnetic nanoparticles was studied with a UV-Vis spectrum (UV-Vis) and fluorescence electron microscopy and Bradford method. Results showed that an XRD spectrum with a peak at (311) corresponded to the standard peak of magnetic nanoparticles. In addition, the magnetic nanoparticles withd≥30 nm have higher saturation magnetizations in comparison with the smaller ones withd≤10 nm. However, the smaller magnetic nanoparticles offered higher efficiency for binding of protein A, due to the high surface/volume ratio. These particles with functional groups on their surface are promising candidates for biomedical applications, e.g., drug delivery, controlled drug release, or disease diagnosis in point-of-care test.

The spectral properties of Fano resonance generated in multilayer dielectric gratings (MDGs) are reported and numerically investigated in this paper. We examine the MDG consisting of numerous identically alternative chalcogenide glass (As₂S₃) and silica (SiO₂) multilayers with several grating widths inscribed through the structure, emphasizing quality (Q) and asymmetric (q) factors. Manipulation of Fano lineshape and its linear characteristics can be achieved by tailoring the layers’ amount and grating widths so that the proposed structure can be applicable for several optical applications. Moreover, we demonstrate the switching/bistability behaviors of the MDG at Fano resonance which provide a significant switching intensity reduction compared to the established Lorentzian resonant structures.