Highly Sensitive Terahertz Metasurface Based on Electromagnetically Induced Transparency-Like Resonance in Detection of Skin Cancer Cells.

Terahertz (THz) metasurfaces based on high Q-factor electromagnetically induced transparency-like (EIT-like) resonances are promising for biological sensing. Despite this potential, they have not often been investigated for practical differentiation between cancerous and healthy cells. The present methodology relies mainly on refractive index sensing, while factors of transmission magnitude and Q-factor offer significant information about the tumors. To address this limitation and improve sensitivity, we fabricated a THz EIT-like metasurface based on asymmetric resonators on an ultra-thin and flexible dielectric substrate. Bright-dark modes coupling at 1.96 THz was experimentally verified, and numerical results and theoretical analysis were presented. An enhanced theoretical sensitivity of 550 GHz/RIU was achieved for a sample with a thickness of 13 µm due to the ultra-thin substrate and novel design. A two-layer skin model was generated whereby keratinocyte cell lines were cultured on a base of collagen. When NEB1-shPTCH (basal cell carcinoma (BCC)) were switched out for NEB1-shCON cell lines (healthy) and when BCC's density was raised from 1 × 105 to 2.5 × 105, a frequency shift of 40 and 20 GHz were observed, respectively. A combined sensing analysis characterizes different cell lines. The findings may open new opportunities for early cancer detection with a fast, less-complicated, and inexpensive method.

Measuring Open Porosity of Porous Materials Using THz-TDS and an Index-Matching Medium.

The porosity of porous materials is a critical quality attribute of many products ranging from catalysis and separation technologies to porous paper and pharmaceutical tablets. The open porosity in particular, which reflects the pore space accessible from the surface, is crucial for applications where a fluid needs to access the pores in order to fulfil the functionality of the product. This study presents a methodology that uses terahertz time-domain spectroscopy (THz-TDS) coupled with an index-matching medium to measure the open porosity and analyze scattering losses of powder compacts. The open porosity can be evaluated without the knowledge of the refractive index of the fully dense material. This method is demonstrated for pellets compressed of pharmaceutical-grade lactose powder. Powder was compressed at four different pressures and measured by THz-TDS before and after they were soaked in an index-matching medium, i.e., paraffin. Determining the change in refractive index of the dry and soaked samples enabled the calculation of the open porosity. The results reveal that the open porosity is consistently lower than the total porosity and it decreases with increasing compression pressure. The scattering losses reduce significantly for the soaked samples and the scattering centers (particle and/or pore sizes) are of the order of or somewhat smaller than the terahertz wavelength. This new method facilitates the development of a better understanding of the links between material properties (particles size), pellet properties (open porosity) and performance-related properties, e.g., disintegration and dissolution performance of pharmaceutical tablets.

Industrial Applications of Terahertz Sensing: State of Play.

This paper is a survey of existing and upcoming industrial applications of terahertz technologies, comprising sections on polymers, paint and coatings, pharmaceuticals, electronics, petrochemicals, gas sensing, and paper and wood industries. Finally, an estimate of the market size and growth rates is given, as obtained from a comparison of market reports.

Terahertz time-domain spectroscopy as a novel metrology tool for liquid-phase exfoliated few-layer graphene.

Few-layer graphene (FLG) platelets exfoliated directly from graphite are finding a wide range of potential applications, including composites and printed electronics. However, characterisation of the FLG material following incorporation into polymers, including the quality of the dispersion, remains a challenge. Here, we present the use of terahertz time-domain spectroscopy as a potential solution to this challenge which could form the basis of a rapid characterisation tool. The THz refractive index was found to be highly sensitive to the loading of FLG, opening the route to mapping local FLG concentration within a polymer composite sample. By fitting the measured permittivity of the flakes to the Drude-Smith model of conductivity, we also show that the carrier concentrations of these materials are comparable to un-doped chemical vapour deposition produced materials. The ability to measure electronic properties of FLG following processing is important to ensure that defects have not been introduced or chemical functionalisation removed during processing.

Covalent Carbene Functionalization of Graphene: Toward Chemical Band-Gap Manipulation.

In this work, we employ dibromocarbene (DBC) radicals to covalently functionalize solution exfoliated graphene via the formation of dibromocyclopropyl adducts. This is achieved using a basic aqueous/organic biphasic reaction mixture to decompose the DBC precursor, bromoform, in conjunction with a phase-transfer catalyst to facilitate ylide formation and carbene migration to graphene substrates. DBC-functionalized graphene (DBC-graphene) was characterized using a range of spectroscopic and analytical techniques to confirm the covalent nature of functionalization. Modified optical and electronic properties of DBC-graphene were investigated using UV-vis spectroscopy, analysis of electrical I-V transport properties, and noncontact terahertz time-domain spectroscopy. The implications of carbene functionalization of graphene are considered in the context of scalable radical functionalization methodologies for bulk-scale graphene processing and controlled band-gap manipulation of graphene.

Dispersion properties of sulfur doped gallium selenide crystals studied by THz TDS.

High optical quality nonlinear crystals of solid solution GaSe(1-x)S(x), x=0, 0.05, 0.11, 0.22, 0.29, 0.44, 1 were grown by modified Bridgman method with heat field rotation. Ordinary and extraordinary wave dispersion was studied in detail as a function of sulfur content by terahertz time-domain spectroscopy (THz TDS) in the 0.3-4 THz range using cleaved and processed (cut and polished) crystals. Suitable dispersion equations for different parts of the entire transparency range were derived, utilizing comparative analyses of the measured data, the available published data, and approximations in the form of Sellmeier equations. A criterion was proposed for selecting measurement results of adequate quality, based on the etalon patterns in the transmission spectrum.

Investigation of optical and structural properties of ceramic boron nitride by terahertz time-domain spectroscopy.

Six types of hexagonal boron nitride are investigated by terahertz time-domain spectroscopy. The loss coefficient is shown to be linear with porosity, while variations in refractive index indicate the distribution of porosity within the structure. Pyrolytic boron nitride is demonstrated to be suitable as a terahertz optical material.

Terahertz reflectivities of metal-coated mirrors.

Terahertz (THz) reflectivities of a variety of metal-coated mirrors were measured. Gold, silver, and aluminum coatings were tested and compared. It was found that all types of optical metal-coated mirrors perform equally well as THz reflectors.

Methodologies for determining the dynamic ranges and signal-to-noise ratios of terahertz time-domain spectrometers.

We discuss procedures for calculating the signal-to-noise ratios and the dynamic ranges of terahertz time-domain spectrometers. We also offer recommendations for standardized calculations for time-domain and frequency-domain data.

Linearity calibration of amplitude and power measurements in terahertz systems and detectors.

We describe a device consisting of a set of silicon plates to be employed for calibrating the linearity of amplitude/power measurements of terahertz systems and detectors. The device is used to test a time-domain spectrometer, a pyroelectric sensor, and a Golay cell. The results demonstrate that the linearity of amplitude/power measurement cannot be assumed but must be experimentally verified.