A Novel Plasmonic Nanoantenna-Based Sensor for Illicit Materials and Drugs Detection

Terahertz (THz) spectroscopy and imaging are of significant interest in molecular detection and identification. Illicit drugs are characterized by a different absorption spectrum, with sharp absorption peaks located in the terahertz frequency range. In this article, the design, simulation, and fabrication of two novel plasmonic nanoantennas with resonance frequencies over the 1–10 THz range for illicit materials and drugs detection are proposed. The first nanoantenna, called the butterfly nanoantenna, is composed of two symmetrical butterfly shaped gold arms with a length of 46.48 μm, width of 22.40 μm, and thickness of 200 nm, separated by a gap of 20 nm. The two-layer substrate consists of 3 μm silicon and 50 nm gold. The results of the simulation, performed by the 3D CST Studio Suite 2023, show three different resonance frequencies at 2.1 THz, 3.6 THz, and 5.1 THz respectively, with a -10 dB S 11 lower than -18 dB and directivity of up to 11.04 dBi. Starting from the single butterfly nanoantenna design, a novel geometrical nanoantenna, called the shamrock nanoantenna, is composed of three symmetrical arms, each with a lenght of 23.14 μm, width of 22.40 μm, and thickness of 200 nm, separated by a central gap of 20 nm is introduced. The simulation results show two different resonance frequencies at 1.9 THz and 3.3 THz, with -10 dB S 11 lower than -26 dB and -20 dB, respectively. A sensitivity of 1500 GHz/RIU at 1.9 THz, 2500 GHz/RIU at 2.1 THz, 6000 GHz/RIU at 3.3 THz, 10000 GHz/RIU at 3.6 THz, 11500 GHz/RIU at 5.1 THz is theoretically observed for the detection of illecit materials and drugs with a thickness of 5 μm of analyte. The multiband sensor based on the proposed plasmonic nanoantennas with an enhancement factor of 6.09×10 5 shows a very broad observation range providing a non-destructive method

Scanning the issue: T-ray imaging, sensing, and retection

Copyright © 2007 IEEEDerek Abbott, Xi-Cheng Zhan

Advantages and limitations of spectroscopic, chromatographic and electrophoretic methods for the characterisation of synthetic cannabinoids and synthetic cathinone derivatives

Over the last decade new psychoactive substances (NPS) flooded Europe and the challenging task for drug law enforcement is how to effectively respond to the dynamically and constantly changing drug market. NPS are regarded as legal alternatives to internationally controlled drugs of abuse. NPS are sold via the internet as, inter alia, “designer drugs”, “legal highs”, or “bath salts” in colourful and professionally designed packages mixed with herbal products or as pure powder. There is a persisting race between the legal prosecution and the producers of designer drugs as those strive to be one step ahead by rapidly generating new NPS products in reaction to new legislative measures. The rapid emergence of novel products means that developing and maintaining selective analytical methods and reference standards is challenging. Beside laboratory methods, the demand for portable analytics is high given the versatile distribution channels and the related particular risk for public institutions handling these products including postal delivery facilities, custom controls and prisons. In this thesis, new analytical methods were developed for the detection of synthetic cannabinoids and synthetic cathinones, the most frequently seized NPS subgroups. An ion mobility spectrometry (IMS) method was developed as an in-field alternative presumptive test for the non-destructive and selective detection of NPS in different matrices by wiping the surface of a sample with a swab. The suitability of the method for on-site analysis was demonstrated in a prison in Rhineland-Palatinate. The contactless and non-destructive detection of NPS was investigated using THz radiation for the first time. Fast characterisation of newly emerged and unknown substances was examined using portable and laboratory-based Raman spectrometers. Data analysis used a combination of a newly developed principal component analysis model and frequency tables. In addition, it was shown, that the analysis of herbal mixtures was possible using a simple solid/liquid extraction followed by precipitation of the synthetic cannabinoid constituents. New laboratory methods were developed to complement the screening techniques. The possibility to quantify NPS via the calibration curves of a small set of NPS, for which reference material is commercially available was demonstrated and validated via the analysis of seizures using ultra-performance liquid chromatography-diode array detection. Finally, capillary electrophoresis-diode array detection with a chiral selector was used for the chiral discrimination of NPS in the form of a general unknown screening method for mixtures and bulking agents on the one hand and a high throughput method for the fast analysis of single substances on the other hand. With the methods developed here, the analytical portfolio of NPS drug analysis was greatly expanded to meet the challenges of the dynamically and constantly changing drug market. All methods were successfully applied to real samples and partly in routine analysis in different criminal investigations offices and in public institutions (Wittlich prison)

Biosensing with T-ray spectroscopy

Copyright © 2007 SPIE - The International Society for Optical Engineering Copyright 2007 Society of Photo-Optical Instrumentation Engineers. This paper was published in Biophotonics 2007: Optics in Life Science, edited by Jürgen Popp, Gert von Bally, Proc. of SPIE-OSA Biomedical Optics, SPIE Vol. 6633, 66331D and is made available as an electronic reprint with permission of SPIE. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.In the recent years, it has been shown that terahertz (or T-ray) spectroscopy is a versatile tool for biosensing and safety applications. This is due to the fact that the THz-spectra of many biomolecules show very characteristic, distinct spectroscopic features. Furthermore, most non-metallic packaging materials are nearly transparent in this frequency range (0.1-6 THz, 3 cm-1-200 cm-1), so that it is possible to non-invasively identify even sealed substances like pharmaceuticals, illicit drugs or explosives by their spectroscopic signatures. This opens a significant potential for a wide range of applications from quality control of pharmaceutical substances via safety applications through to biomedical applications. The individual spectroscopic features below approximately 5 THz that spurred the increased world wide interest in T-ray spectroscopy are mainly due to intermolecular rather than intramolecular vibrations in the polycrystalline samples. The spectra of more complex biomolecules, like proteins and nucleotides, typically show less or even no sharp features, due to the lack of long-range intermolecular order. Furthermore, due to the typically significantly smaller sample amount, the signal to noise ratio is strongly increased. Water shows a strong absorption in this frequency range, which all together makes real biomedical applications of T-ray spectroscopy rather difficult. Yet, by combining a careful sample preparation, novel experimental techniques and an advanced signal processing of the experimental data we can still clearly distinguish between even complex biomolecules and therefore demonstrate the potential the technique holds for biomedical applications. © 2007 SPIE-OSA.Bernd M. Fischer, Hanspeter Helm and Derek Abbot

Microscopy of terahertz spoof surface plasmons propagating on planar metamaterial waveguides

Surface plasmon polaritons (SPPs) are electromagnetic waves that have attracted significant interest owing to their subwavelength confinement and the strong field enhancement that they provide. Yet in the terahertz (THz) frequency region of the spectrum, which is well below the plasma frequency of metals, these surface waves are characterized by extremely weak confinement that has severely limited their exploitation for information processing and sensing. One means to circumvent this limitation is through subwavelength structuring of a metallic surface, which can thereby be engineered to support the propagation of spoof surface plasmon polaritons (SSPPs) that closely mimic the properties of SPPs. In this work, we report the design and experimental characterization of an ultra-thin metamaterial planar waveguide that supports SSPPs at THz frequencies. Finite-element method simulations are shown to predict the excitation of SSPPs on the surface of our devices under free-space illumination at 3.45 THz. We investigate these structures experimentally using THz scattering-type scanning near-field microscopy (THz-s-SNOM) to map directly the out-of-plane electric field associated with the propagation of SSPPs on the surface of the waveguides. Our work paves the way for the future development of plasmonic integrated circuit technologies and components operating in the THz frequency band

Explosive Detection Equipment and Technology for Border Security

This report contains a brief survey of Explosives Detection Technology,as it is applied for inspection of goods and passengers at borders, and explains the role of European legislation and the European Commission¿s research programs in this field. It describes the techniques of trace and bulk explosives detection that are in use, the latest techniques that are in development and the characteristics of explosives that are, or might be, used to provide a signature for exploitation in detection technology. References to academic reviews are included for those wishing to study the subject in greater depth. Some additional details are given concerning plastic and liquid explosives, which are a threat of particular current importance. The report also contains a brief account of relevant European trade, safety and security legislation, a description of recent policy initiatives and tables of related European Commission funded research projects. Contact details of commercial companies selling explosive detection products are also provided.JRC.G.6-Sensors, radar technologies and cybersecurit

Terahertz Spectroscopy for Gastrointestinal Cancer Diagnosis

In this chapter, we present a number of sensitive measurement modalities for the study and analysis of human cancer-affected colon and gastric tissue using terahertz (THz) spectroscopy. Considerable advancements have been reached in characterization of bio-tissue with some accuracy, although too dawn, and still long and exhaustive work have to be done towards well-established and reliable applications. The advent of the THz-time-domain spectroscopy (THz-TDS) test modality at a sub-picosecond time resolution has arguably fostered an intensive work in this field’s research line. The chapter addresses some basic theoretical aspects of this measurement modality with the presentation of general experimental laboratory setup diagrams for THz generation and detection, sample preparation aspects, samples optical parameters calculation procedures and data analysis

Octave-spanning broadband absorption of terahertz light using metasurface fractal-cross absorbers

Synthetic fractals inherently carry spatially encoded frequency information that renders them as an ideal candidate for broadband optical structures. Nowhere is this more true than in the terahertz (THz) band where there is a lack of naturally occurring materials with valuable optical properties. One example are perfect absorbers that are a direct step toward the development of highly sought after detectors and sensing devices. Metasurface absorbers that can be used to substitute for natural materials suffer from poor broadband performance, while those with high absorption and broadband capability typically involve complex fabrication and design and are multilayered. Here, we demonstrate a polarization-insensitive ultrathin (∼λ/6) planar metasurface THz absorber composed of supercells of fractal crosses capable of spanning one optical octave in bandwidth, while still being highly efficient. A sufficiently thick polyimide interlayer produces a unique absorption mechanism based on Salisbury screen and antireflection responses, which lends to the broadband operation. Experimental peak absorption exceeds 93%, while the average absorption is 83% from 2.82 THz to 5.15 THz. This new ultrathin device architecture, achieving an absorption-bandwidth of one optical octave, demonstrates a major advance toward a synthetic metasurface blackbody absorber in the THz ban

Evaluation of Non-Covalent Interaction Models in Molecular Crystals Using Terahertz Spectroscopy

Density functional theory (DFT) is a powerful tool that can be used to evaluate the low-frequency vibrational spectra of solid-state crystalline materials. Since THz spectroscopy is sensitive to both the intermolecular and intramolecular forces that govern the formation of crystalline materials, it is an ideal tool to investigate the accuracy of calculated DFT crystal structures and their vibrational spectra. When using solid-state DFT, non-covalent dispersion interactions are not fully treated in typical approaches. In order to account for these interactions, the addition of dispersion force correction terms are necessary. A number of methods exist to correct for this deficiency of DFT, and this work investigates the use of semi-empirical London dispersion force correction models. Through the investigation of several small organic molecules, amino acids and related compounds, the standard implementation (referred to as DFT-D) is examined, and the need to alter this standard approach has been identified. Modifications of the scaling factor and atomic parameters within this method have led to more accurate simulations, termed the DFT-DX model. In addition to this work on improving London dispersion force corrections, solid-state DFT calculations with these enhancements can be used to predict the crystal structures of previously unknown or difficult to synthesize materials, such as amino acid hydrates, and achieve detailed information about the internal and external forces in molecular crystals