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Optical metasurface is a combination of manufactured periodic patterns of many artificial nanostructured unit cells, which can provide unique and attractive optical and electrical properties. Additionally, the function of the metasurface can be altered by adjusting the metasurface's size and configuration to satisfy a particular required property. However, once it is fabricated, such specific property is fixed and cannot be changed. Here, phase change material (PCM) can play an important role due to its two distinct states during the phase transition, referred to as amorphous and crystalline states, which exhibit significantly different refractive indices, particularly in the infrared wavelength. Therefore, a combination of metasurface with a phase change material may be attractive for achieving agile and tunable functions. In this paper, we numerically investigate an array of silicon cylinders with a thin PCM layer at their centers. The GST and GSST are the most well-known PCMs and were chosen for this study due to their non-volatile properties. This structure produces two resonant modes, magnetic dipole and electric dipole, at two different resonating wavelengths. We have numerically simulated the effect of cylinder's height and diameter on the reflecting profile, including the effect of thickness of the phase change material. Additionally, it is shown here that a superior performance can be achieved towards reduced insertion loss, enhanced extinction ratio, and increased figure of merit when a GST layer is replaced by a GSST layer.

The increasing use of nanomaterials and scalable, high-yield nanofabrication process are revolutionizing the development of novel biosensors. Over the past decades, researches on nanotechnology-mediated biosensing have been on the forefront due to their potential application in healthcare, pharmaceutical, cell diagnosis, drug delivery, and water and air quality monitoring. The advancement of nanoscale science relies on a better understanding of theory, manufacturing and fabrication practices, and the application specific methods. The topology and tunable properties of nanoparticles, a part of nanoscale science, can be changed by different manufacturing processes, which separate them from their bulk counterparts. In the recent past, different nanostructures, such as nanosphere, nanorods, nanofiber, core–shell nanoparticles, nanotubes, and thin films, have been exploited to enhance the detectability of labelled or label-free biological molecules with a high accuracy. Furthermore, these engineered-materials-associated transducing devices, e.g., optical waveguides and metasurface-based scattering media, widened the horizon of biosensors over a broad wavelength range from deep-ultraviolet to far-infrared. This review provides a comprehensive overview of the major scientific achievements in nano-biosensors based on optical fiber, nanomaterials and terahertz-domain metasurface-based refractometric, labelled and label-free nano-biosensors.

Metamaterials (MMs) are the artificially engineered materials that can exhibit particular electromagnetic properties such as negative refractive index, left-handed behavior, extraordinary transmission, etc. These fascinating properties of MMs are of great and increasing interest to be used in various applications in the terahertz regime (0.1-10 THz). In this study, the electromagnetic property of metamaterial that we are interested is an extraordinary transmission for creating a “Metamaterial Absorber (MMA)”. Over the past decade, there has been a number of designed patterns of metamaterial absorbers having high absorptivity and also multi-absorption characteristics such as split-ring resonator, square, U-shape, T-shape and Hexagon. Most of the Hexagons are designed to have the absorption characteristics in GHz frequency. We intend to investigate the effects of the parameters regarding the absorption in the terahertz regime, especially in 0.3-5.0 THz for various applications such as security and medicine. The proposed absorber structure in this study consists of 3 layers which are a periodically arranged metallic hexagonal pattern layer, a dielectric layer, and a continuous metallic layer. Length, width, number of gaps, gap size, the position of a gap of the hexagon in the first layer are the studied parameters. The proposed hexagon metamaterial absorber of the first design having 5 gaps with gap size 5 μm each located at the corner of the hexagon provide 4 absorption bands with high absorptivity. For the other design having 6 gaps with gap size of 5 μm each located at hexagon side show not only 3 narrow bands of perfect absorption but also a broadband absorbance for the terahertz regime around 3 THz.