Photonic Applications of Metal-Dielectric Heterostructured Nanomaterials

Nanoparticles for Stem Cell Therapy Bioengineering in Glioma

Gliomas are a dismal disease associated with poor survival and high morbidity. Current standard treatments have reached a therapeutic plateau even after combining maximal safe resection, radiation, and chemotherapy. In this setting, stem cells (SCs) have risen as a promising therapeutic armamentarium, given their intrinsic tumor homing as well as their natural or bioengineered antitumor properties. The interplay between stem cells and other therapeutic approaches such as nanoparticles holds the potential to synergize the advantages from the combined therapeutic strategies. Nanoparticles represent a broad spectrum of synthetic and natural biomaterials that have been proven effective in expanding diagnostic and therapeutic efforts, either used alone or in combination with immune, genetic, or cellular therapies. Stem cells have been bioengineered using these biomaterials to enhance their natural properties as well as to act as their vehicle when anticancer nanoparticles need to be delivered into the tumor microenvironment in a very precise manner. Here, we describe the recent developments of this new paradigm in the treatment of malignant gliomas.

Polarization Selectivity of the Thin-Metal-Film Plasmon-Assisted Fiber-Optic Polarizer

The interaction between light and metallic nanostructures leads to many impressive achievements and has a wide range of applications. The thin-metal-film plasmon-assisted fiber-optic polarizer is one of the essential applications. However, the polarization mechanism and the transmitted polarization of the plasmon-assisted polarizer have given rise to controversy over the past decade. Which of the polarizations is preferentially transmitted through the polarizer? The transverse electric polarization or the transverse magnetic polarization? Here, special emphasis is placed upon the polarization mechanism and the transmitted polarization of thin-metal-film plasmon-assisted fiber polarizers. We first investigate the polarization mechanism of the polarizers theoretically and numerically. Furthermore, a novel approach is proposed to demonstrate the transmitted polarization in the plasmon-assisted fiber polarizers experimentally. We demonstrate that the polarization mechanism is based on the polarization selective absorption of the metallic material, and the transverse electric polarization is the only transmitted polarization of the metallic plasmon-assisted polarizer. Moreover, the plasmon-assisted polarizer can offer a high polarization extinction ratio (33.1 dB) and a low insertion loss (1.1 dB) at room temperature and have excellent temperature stability in the range of -48 to 82 °C. Experimental results agree well with our theoretical and numerical analyses. The findings clarify the confusion about the polarization mechanism and the transmitted polarization of metallic plasmon-assisted fiber polarizers over the past decade, providing new ground for the exploration of polarization-sensitive optical systems, with good potential applications in the fields of optical sensors, plasmonic lasers, coherent optical communications, and biosensor systems.

Geometrical Dependence on the Onset of Surface Plasmon Polaritons in THz Grid Metasurfaces

The transmission response of metallo-dielectric grid metasurfaces is experimentally investigated through Terahertz Time Domain Spectroscopy and the corresponding effective dielectric function is retrieved. Using a lumped element model we can determine the dependence of the effective plasma frequency (the transition frequency) on the metasurface filling factor F. The change of the transition frequency vs. F spans over one order of magnitude and sets the threshold between the metamaterial (homogeneous) and the photonic crystal (diffraction-like) regime, ruling the onset of two different Surface Plasmon Polaritons, spoof and high order. Field symmetry and spatial extension of such excitations are investigated for the possible applications of THz grid metasurfaces in bio- and chemical sensing and sub-wavelength imaging.

Optical Properties of Low-Loss Ag Films and Nanostructures on Transparent Substrates

We demonstrate the fabrication of a low-loss single-crystalline Ag nanostructure deposited on transparent substrates. Our approach is based on an epitaxial growth technique in which a NaCl(001) substrate is used. The NaCl substrate is dissolved in water to allow the Ag film to be transferred onto the desired substrates. Focused ion beam milling is subsequently employed to pattern a nanoarray structure consisting of 200 nanorods. The epitaxial Ag films with nanoarray structures grown in the study exhibited very flat and smooth surfaces having excellent crystallinity and local misorientation of less than 1°. Further, spectroscopic ellipsometry measurements indicated that the imaginary part of the dielectric constant of the single-crystalline film was smaller than that of a conventional polycrystalline film. Moreover, we used the three-dimensional finite-difference time-domain method to analyze the plasmonic properties of the nanoarray structure by considering the actual processed structure. Characteristically, when the SiO₂ substrate was etched by ion beam milling to a depth of 30 nm, the spectrum showed a spectral shape 20% sharper than that of the substrate with no etching (depth: 0 nm). The plasmonic performance of the single-crystalline Ag nanostructure was largely determined by its structural precision and the dielectric properties of the metal.

Single source precursor driven phase selective synthesis of Au–CuGaS2 heteronanostructures: an observation of plasmon enhanced photocurrent efficiency

Coupling of metallic Au with CuGaS₂, synthesized from single molecule precursor [Ga(acda)₃Cu(PPh₃)₂]NO₃, results Au–CuGaS₂ heterostructure which shows remarkably high photocurrent response compared to CuGaS₂.

Synthesis of Fluorescent Core-Shell Metal Nanohybrids: A Versatile Approach

A flexible way of fabricating core-shell noble metal-organic nanohybrids with tailored chemical and spectroscopic properties is proposed here. The synthetic protocol consists of a multi-step procedure able to guarantee acceptable reproducibility of core size and shape as well as control of the organic outer layer. The proposed method highlights limitations in obtaining highly controllable products, although the heterogeneity degree of the nanostructures is in line with that expected from bottom-up approaches in solution. Selective functionalization of the nanohybrids with properly-substituted fluorescent dyes under variable experimental conditions allowed the preparation of composite systems of tunable spectroscopic properties to be employed as nanoprobes in sensing or photonic applications. To this end, preliminary investigation on embedding the nanohybrids in compatible polymeric matrices is also reported.