The potential of terahertz sensing for cancer diagnosis

A Flexible Terahertz Metamaterial Sensor for Pesticide Sensing and Detection

Terahertz (THz) waves have garnered significant interest across various fields, particularly in high-sensitivity sensing applications. Metamaterials can be employed in THz sensors, specifically for refractive index sensing and pesticide detection due to their high-sensitivity characteristics. In this Article, a dual-band flexible THz metamaterial sensor based on polyimide is proposed for refractive index and pesticide sensing, which is fabricated using ultraviolet (UV) lithography technology and measured by a THz time-domain spectroscope (TDS) system. The resonant frequencies of the sensor are at 0.37 and 1.13 THz, with transmission rates of 2.9% and 0.3%, respectively. With an analyte layer attached to the sensor's surface, the sensitivity of refractive index sensing can be calculated as 0.09 and 0.28 THz/RIU (refractive index unit) at the two resonant frequencies. In order to validate the exceptional pesticide sensing performance of the sensor, chlorpyrifos-methyl acetone solutions with various concentrations are added on it. Furthermore, a monolayer of graphene is coated on the sensor's surface, which is proved capable of improving pesticide sensing sensitivity at low concentrations due to strong π-π stacking interactions with π-electrons in chlorpyrifos-methyl solutions. Therefore, the graphene-coated sensor can be utilized in detecting pesticide solutions with low concentrations, and the sensor without graphene is preferred for high concentration detection. This work provides a novel option for the THz metamaterial sensor with high sensitivity covering a wide pesticide concentration range.

Biomedical application of terahertz imaging technology: a narrative review

Background and Objective

Terahertz (THz) imaging has wide applications in biomedical research due to its properties, such as non-ionizing, non-invasive and distinctive spectral fingerprints. Over the past 6 years, the application of THz imaging in tumor tissue has made encouraging progress. However, due to the strong absorption of THz by water, the large size, high cost, and low sensitivity of THz devices, it is still difficult to be widely used in clinical practice. This paper provides ideas for researchers and promotes the development of THz imaging in clinical research.

Methods

The literature search was conducted in the Web of Science and PubMed databases using the keywords "Terahertz imaging", "Breast", "Brain", "Skin" and "Cancer". A total of 94 English language articles from 1 January, 2017 to 30 December, 2022 were reviewed.

Key Content and Findings

In this review, we briefly introduced the recent advances in THz near-field imaging, single-pixel imaging and real-time imaging, the applications of THz imaging for detecting breast, brain and skin tissues in the last 6 years were reviewed, and the advantages and existing challenges were identified. It is necessary to combine machine learning and metamaterials to develop real-time THz devices with small size, low cost and high sensitivity that can be widely used in clinical practice. More powerful THz detectors can be developed by combining graphene, designing structures and other methods to improve the sensitivity of the devices and obtain more accurate information. Establishing a THz database is one of the important methods to improve the repeatability and accuracy of imaging results.

Conclusions

THz technology is an effective method for tumor imaging. We believe that with the joint efforts of researchers and clinicians, accurate, real-time, and safe THz imaging will be widely applied in clinical practice in the future.

A graphene/h-BN MEMS varactor for sub-THz and THz applications

Recent development of terahertz systems has created the need for new elements operating in this frequency band, i.e., fast tunable devices such as varactors. Here, we present the process flow and characterization of a novel electronic variable capacitor device that is made with the use of 2D metamaterials such as graphene (GR) or hexagonal boron nitride (h-BN). Comb-like structures are etched into a silicon/silicon nitride substrate and a metal electrode is deposited at the bottom. Next, a PMMA/GR/h-BN layer is placed on top of the sample. As voltage is applied between GR and metal, the PMMA/GR/h-BN layer bends towards the bottom electrode thus decreasing the distance between electrodes and changing the capacitance. The high tunability and complementary metal oxide semiconductor (CMOS)-compatible process flow of the platform for our device and its millimeter size make it promising for applications in future electronics and terahertz technologies. The goal of our research is to integrate our device with dielectric rod waveguides, thus making THz phase shifters.

Metasurface-Assisted Terahertz Sensing

Terahertz (THz) waves, which fall between microwaves and infrared bands, possess intriguing electromagnetic properties of non-ionizing radiation, low photon energy, being highly sensitive to weak resonances, and non-polar material penetrability. Therefore, THz waves are extremely suitable for sensing and detecting chemical, pharmaceutical, and biological molecules. However, the relatively long wavelength of THz waves (30~3000 μm) compared to the size of analytes (1~100 nm for biomolecules, <10 μm for microorganisms) constrains the development of THz-based sensors. To circumvent this problem, metasurface technology, by engineering subwavelength periodic resonators, has gained a great deal of attention to enhance the resonance response of THz waves. Those metasurface-based THz sensors exhibit high sensitivity for label-free sensing, making them appealing for a variety of applications in security, medical applications, and detection. The performance of metasurface-based THz sensors is controlled by geometric structure and material parameters. The operating mechanism is divided into two main categories, passive and active. To have a profound understanding of these metasurface-assisted THz sensing technologies, we review and categorize those THz sensors, based on their operating mechanisms, including resonators for frequency shift sensing, nanogaps for enhanced field confinement, chirality for handedness detection, and active elements (such as graphene and MEMS) for advanced tunable sensing. This comprehensive review can serve as a guideline for future metasurfaces design to assist THz sensing and detection.

Terahertz Nonlinear Ghost Imaging via Plane Decomposition: Toward Near-Field Micro-Volumetry

Terahertz time-domain imaging targets the reconstruction of the full electromagnetic morphology of an object. In this spectral range, the near-field propagation strongly affects the information in the space-time domain in items with microscopic features. While this often represents a challenge, as the information needs to be disentangled to obtain high image fidelity, here, we show that such a phenomenon can enable three-dimensional microscopy. Specifically, we investigate the capability of the time-resolved nonlinear ghost imaging methodology to implement field-sensitive micro-volumetry by plane decomposition. We leverage the temporally resolved, field-sensitive detection to "refocus" an image plane at an arbitrary distance from the source, which defines the near-field condition, and within a microscopic sample. Since space-time coupling rapidly evolves and diffuses within subwavelength length scales, our technique can separate and discriminate the information originating from different planes at different depths. Our approach is particularly suitable for objects with sparse micrometric details. Building upon this principle, we demonstrate complex, time-domain volumetry resolving internal object planes with subwavelength resolution, discussing the range of applicability of our technique.

Double-negative metamaterial square enclosed Q.S.S.R For microwave sensing application in S-band with high sensitivity and Q-factor

Metamaterials have gained much attention due to their exciting characteristics and potential uses in constructing valuable technologies. This paper presents a double negative square resonator shape metamaterial sensor to detect the material and its thickness. An innovative double-negative metamaterial sensor for microwave sensing applications is described in this paper. It has a highly sensitive Q-factor and has good absorption characteristics approximately equal to one. For the metamaterial sensor, the recommended measurement is 20 by 20 mm. Computer simulation technology (C.S.T.) microwave studios are used to design the metamaterial structure and figure out its reflection coefficient. Various parametric analyses have been performed to optimize the design and size of the structure. The experimental and theoretical results are shown for a metamaterial sensor that is attached to five different materials such as, Polyimide, Rogers RO3010, Rogers RO4350, Rogers RT5880, and FR-4. A sensor's performance is evaluated using three different thicknesses of FR-4. There is a remarkable similarity between the measured and simulated outcomes. The sensitivity values for 2.88 GHz and 3.5 GHz are 0.66% and 0.19%, respectively, the absorption values for both frequencies are 99.9% and 98.9%, respectively, and the q-factor values are 1413.29 and 1140.16, respectively. In addition, the figure of merit (FOM) is analyzed, and its value is 934.18. Furthermore, the proposed structure has been tested against absorption sensor applications for the purpose of verifying the sensor's performance. With a high sense of sensitivity, absorption, and Q-factor, the recommended sensor can distinguish between thicknesses and materials in various applications.

Advances in terahertz technology for cancer detection applications

Currently, there is an increasing demand for the diagnostic techniques that provide functional and morphological information with early cancer detection capability. Novel modern medical imaging systems driven by the recent advancements in technology such as terahertz (THz) and infrared radiation-based imaging technologies which are complementary to conventional modalities are being developed, investigated, and validated. The THz cancer imaging techniques offer novel opportunities for label free, non-ionizing, non-invasive and early cancer detection. The observed image contrast in THz cancer imaging studies has been mostly attributed to higher refractive index, absorption coefficient and dielectric properties in cancer tissue than that in the normal tissue due the local increase of the water molecule content in tissue and increased blood supply to the cancer affected tissue. Additional image contrast parameters and cancer biomarkers that have been reported to contribute to THz image contrast include cell structural changes, molecular density, interactions between agents (e.g., contrast agents and embedding agents) and biological tissue as well as tissue substances like proteins, fiber and fat etc. In this paper, we have presented a systematic and comprehensive review of the advancements in the technological development of THz technology for cancer imaging applications. Initially, the fundamentals principles and techniques for THz radiation generation and detection, imaging and spectroscopy are introduced. Further, the application of THz imaging for detection of various cancers tissues are presented, with more focus on the in vivo imaging of skin cancer. The data processing techniques for THz data are briefly discussed. Also, we identify the advantages and existing challenges in THz based cancer detection and report the performance improvement techniques. The recent advancements towards THz systems which are optimized and miniaturized are also reported. Finally, the integration of THz systems with artificial intelligent (AI), internet of things (IoT), cloud computing, big data analytics, robotics etc. for more sophisticated systems is proposed. This will facilitate the large-scale clinical applications of THz for smart and connected next generation healthcare systems and provide a roadmap for future research.

The Convergence of FTIR and EVs: Emergence Strategy for Non-Invasive Cancer Markers Discovery

In conjunction with imaging analysis, pathology-based assessments of biopsied tissue are the gold standard for diagnosing solid tumors. However, the disadvantages of tissue biopsies, such as being invasive, time-consuming, and labor-intensive, have urged the development of an alternate method, liquid biopsy, that involves sampling and clinical assessment of various bodily fluids for cancer diagnosis. Meanwhile, extracellular vesicles (EVs) are circulating biomarkers that carry molecular profiles of their cell or tissue origins and have emerged as one of the most promising biomarkers for cancer. Owing to the biological information that can be obtained through EVs' membrane surface markers and their cargo loaded with biomolecules such as nucleic acids, proteins, and lipids, EVs have become useful in cancer diagnosis and therapeutic applications. Fourier-transform infrared spectroscopy (FTIR) allows rapid, non-destructive, label-free molecular profiling of EVs with minimal sample preparation. Since the heterogeneity of EV subpopulations may result in complicated FTIR spectra that are highly diverse, computational-assisted FTIR spectroscopy is employed in many studies to provide fingerprint spectra of malignant and non-malignant samples, allowing classification with high accuracy, specificity, and sensitivity. In view of this, FTIR-EV approach carries a great potential in cancer detection. The progression of FTIR-based biomarker identification in EV research, the rationale of the integration of a computationally assisted approach, along with the challenges of clinical translation are the focus of this review.

The distinguishing electrical properties of cancer cells

In recent decades, medical research has been primarily focused on the inherited aspect of cancers, despite the reality that only 5-10% of tumours discovered are derived from genetic causes. Cancer is a broad term, and therefore it is inaccurate to address it as a purely genetic disease. Understanding cancer cells' behaviour is the first step in countering them. Behind the scenes, there is a complicated network of environmental factors, DNA errors, metabolic shifts, and electrostatic alterations that build over time and lead to the illness's development. This latter aspect has been analyzed in previous studies, but how the different electrical changes integrate and affect each other is rarely examined. Every cell in the human body possesses electrical properties that are essential for proper behaviour both within and outside of the cell itself. It is not yet clear whether these changes correlate with cell mutation in cancer cells, or only with their subsequent development. Either way, these aspects merit further investigation, especially with regards to their causes and consequences. Trying to block changes at various levels of occurrence or assisting in their prevention could be the key to stopping cells from becoming cancerous. Therefore, a comprehensive understanding of the current knowledge regarding the electrical landscape of cells is much needed. We review four essential electrical characteristics of cells, providing a deep understanding of the electrostatic changes in cancer cells compared to their normal counterparts. In particular, we provide an overview of intracellular and extracellular pH modifications, differences in ionic concentrations in the cytoplasm, transmembrane potential variations, and changes within mitochondria. New therapies targeting or exploiting the electrical properties of cells are developed and tested every year, such as pH-dependent carriers and tumour-treating fields. A brief section regarding the state-of-the-art of these therapies can be found at the end of this review. Finally, we highlight how these alterations integrate and potentially yield indications of cells' malignancy or metastatic index.

A review of Optical Point-of-Care devices to Estimate the Technology Transfer of These Cutting-Edge Technologies

Despite the remarkable development related to Point-of-Care devices based on optical technology, their difficulties when used outside of research laboratories are notable. In this sense, it would be interesting to ask ourselves what the degree of transferability of the research work to the market is, for example, by analysing the relation between the scientific work developed and the registered one, through patent. In this work, we provide an overview of the state-of-the-art in the sector of optical Point-of-Care devices, not only in the research area but also regarding their transfer to market. To this end, we explored a methodology for searching articles and patents to obtain an indicator that relates to both. This figure of merit to estimate this transfer is based on classifying the relevant research articles in the area and the patents that have been generated from these ones. To delimit the scope of this study, we researched the results of a large enough number of publications in the period from 2015 to 2020, by using keywords "biosensor", "optic", and "device" to obtain the most representative articles from Web of Science and Scopus. Then, we classified them according to a particular classification of the optical PoC devices. Once we had this sampling frame, we defined a patent search strategy to cross-link the article with a registered patent (by surfing Google Patents) and classified them accordingly to the categories described. Finally, we proposed a relative figure called Index of Technology Transference (IoTT), which estimates to what extent our findings in science materialized in published articles are protected by patent.

Measurement and Modeling of the Optical Properties of Adipose Tissue in the Terahertz Range: Aspects of Disease Diagnosis

In this paper, the measurement and modeling of optical properties in the terahertz (THz) range of adipose tissue and its components with temperature changes were performed. Spectral measurements were made in the frequency range 0.25–1 THz. The structural models of main triglycerides of fatty acids are constructed using the B3LYP/6-31G(d) method and the Gaussian03, Revision B.03 program. The optical density (OD) of adipose tissue samples decreases as temperature increases, which can be associated mostly with the dehydration of the sample. Some inclusion of THz wave scattering suppression into the OD decrease can also be expected due to refractive index matching provided by free fatty acids released from adipocytes at thermally induced cell lipolysis. It was shown that the difference between the THz absorption spectra of water and fat makes it possible to estimate the water content in adipose tissue. The proposed model was verified on the basis of molecular modeling and a comparison with experimental data for terahertz spectra of adipose tissue during its heating. Knowing the exact percentage of free and bound water in adipose tissue can help diagnose and monitor diseases, such as diabetes, obesity, and cancer.

Selection criteria of image reconstruction algorithms for terahertz short-range imaging applications

Terahertz (THz) imaging has been regarded as cutting-edge technology in a wide range of applications due to its ability to penetrate through opaque materials, non-invasive nature, and its increased bandwidth capacity. Recently, THz imaging has been extensively researched in security, driver assistance technology, non-destructive testing, and medical applications. The objective of this review is to summarize the selection criteria for current state-of-the-art THz image reconstruction algorithms developed for short-range imaging applications over the last two decades. Moreover, we summarize the selected algorithms' performance and their implementation process. This study provides an in-depth understanding of the fundamentals of image reconstruction algorithms related to THz short-range imaging and future aspects of algorithm processing and selection.

Cost-Effective Bull's Eye Aperture-Style Multi-Band Metamaterial Absorber at Sub-THz Band: Design, Numerical Analysis, and Physical Interpretation

Theoretical and numerical studies were conducted on plasmonic interactions at a polarization-independent semiconductor-dielectric-semiconductor (SDS) sandwiched layer design and a brief review of the basic theory model was presented. The potential of bull's eye aperture (BEA) structures as device elements has been well recognized in multi-band structures. In addition, the sub-terahertz (THz) band (below 1 THz frequency regime) is utilized in communications and sensing applications, which are in high demand in modern technology. Therefore, we produced theoretical and numerical studies for a THz-absorbing-metasurface BEA-style design, with N-beam absorption peaks at a sub-THz band, using economical and commercially accessible materials, which have a low cost and an easy fabrication process. Furthermore, we applied the Drude model for the dielectric function of semiconductors due to its ability to describe both free-electron and bound systems simultaneously. Associated with metasurface research and applications, it is essential to facilitate metasurface designs to be of the utmost flexible properties with low cost. Through the aid of electromagnetic (EM) coupling using multiple semiconductor ring resonators (RRs), we could tune the number of absorption peaks between the 0.1 and 1.0 THz frequency regime. By increasing the number of semiconductor rings without altering all other parameters, we found a translation trend of the absorption frequencies. In addition, we validated our spectral response results using EM field distributions and surface currents. Here, we mainly discuss the source of the N-band THz absorber and the underlying physics of the multi-beam absorber designed structures. The proposed microstructure has ultra-high potentials to utilize in high-power THz sources and optical biomedical sensing and detection applications based on opto-electronics technology based on having multi-band absorption responses.

High anti-interference dual-parameter sensor using an EIT-like effect photonic crystal cavity coupled system

We propose a sensor with high anti-interference ability using a photonic crystal cavity coupled system for simultaneous sensing of the refractive index (RI) and temperature (T) based on an electromagnetically induced transparency-like effect. A transparent window is achieved in the transmission spectrum through destructive interference between the air mode resonance and dielectric mode resonance in two one-dimensional photonic crystal structures. The T-sensitive material (SU-8) is used in the coupled system, promoting sensitivity and anti-interference ability. The capability of the system to simultaneously detect a small range of RI and T is demonstrated using three-dimensional finite-difference time-domain simulations and the fitting process. The RI sensitivities for the air and dielectric modes were 215 nm/refractive index unit (RIU) and 0 nm/RIU, respectively. The T sensitivities for the air and dielectric modes were 19 pm/K and -83pm/K, respectively. The sensor resists external interference, enabling it to resist the error caused by readings. The footprint of the sensor is 29×1.8µm² (length×width), contributing to future optical on-chip integration sensor design.

Improving the accuracy of tumor surgery by THz imaging and making the results of pathological anatomy faster by THz spectroscopy

Background

The terahertz radiation is a specific part of the electromagnetic radiation spectrum and has multiple significant applications in multiple scientific researches such as the applications in the medicine. An important application of the terahertz is its use in tumor imaging which is very important in the tumor surgery; however, lots of physicians and workers in the medical field have little information or having no information at all, dealing with this significant part of the electromagnetic spectrum.

Results

In this work, we interviewed a number of local surgeons in Syrian Arab Republic, who reported that they visually delineate the contour of tumors to be removed, and in order to reduce the number of future possible interventions, a large margin of healthy tissue is often excised. Furthermore, a number of pathologists who reported that preparing samples of excised tissues for examination takes a long period of time which may extend to several days, and that the results of histopathology indicate in some cases the integrity of removed tissues.

Conclusion

We have found that a significant number of participants in the survey demonstrated that the importance of dealing with terahertz imaging and terahertz spectroscopy, encouraging to implement the technique in the Syrian Arab Republic.

Recent advancements in optical biosensors for cancer detection

Optical biosensors are rapid, real-time, and portable, have a low detection limit and a high sensitivity, and have a great potential for diagnosing various types of cancer. Optical biosensors can detect cancer in a few million malignant cells, in comparison to conventional diagnosis techniques that use 1 billion cells in tumor tissue with a diameter of 7 nm-10 nm. Current cancer detection methods are also costly, inconvenient, complex, time consuming, and require technical specialists. This review focuses on recent advances in optical biosensors for early detection of cancer. It is primarily concerned with advancements in the design of various biosensors using resonance, scattering, chemiluminescence, luminescence, interference, fluorescence, absorbance or reflectance, and various fiber types. The development of various two-dimensional materials with optical properties such as biocompatibility, field enhancement, and a higher surface-to-volume ratio, as well as advancements in microfabrication technologies, have accelerated the development of optical sensors for early detection of cancer and other diseases. Surface enhanced Raman spectroscopy technology has the potential to detect a single molecule with high specificity, and terahertz waves are a recently explored technology for cancer detection. Due to the low electromagnetic interference, small size, multiplexing, and remote sensing capabilities of optical fiber-based platforms, they may be a driving force behind the rapid development of biosensors. The advantages and disadvantages of existing and future optical biosensor designs for cancer detection are discussed in detail. Additionally, a prospect for future advancements in the development of optical biosensors for point-of-care and clinical applications is highlighted.

Polarization insensitive symmetrical structured double negative (DNG) metamaterial absorber for Ku-band sensing applications

Metamaterial absorber (MMA) is now attracting significant interest due to its attractive applications, such as thermal detection, sound absorption, detection for explosive, military radar, wavelength detector, underwater sound absorption, and various sensor applications that are the vital part of the internet of things. This article proposes a modified square split ring resonator MMA for Ku-band sensing application, where the metamaterial structure is designed on FR-4 substrate material with a dielectric constant of 4.3 and loss tangent of 0.025. Perfect absorption is realized at 14.62 GHz and 16.30 GHz frequency bands, where peak absorption is about 99.99% for both frequency bands. The proposed structure shows 70% of the average absorption bandwidth of 420 MHz (14.42–14.84 GHz) and 480 MHz (16.06–16.54 GHz). The metamaterial property of the proposed structure is investigated for transverse electromagnetic mode (TEM) and achieved negative permittivity, permeability, and refractive index property for each absorption frequency band at 0°, 45°, and 90° polarization angles. Interference theory is also investigated to verify the absorption properties. Moreover, the permittivity sensor application is investigated to verify the sensor performance of the proposed structure. Finally, a comparison with recent works is performed, which shows that the proposed MMA can be a good candidate for Ku-band perfect absorber and sensing applications.

Analogue of electromagnetically induced transparency in a metal-dielectric bilayer terahertz metamaterial

We realize and numerically demonstrate the analogue of electromagnetically induced transparency (EIT) with a high-Q factor in a metal-dielectric bilayer terahertz metamaterial (MM) via bright-bright mode coupling and bright-dark mode coupling. The dielectric MM with silicon dimer rectangular-ring-resonator (Si-DRR) supports either a bright high-Q toroidal dipole resonance (TD) or a dark TD with infinite Q value, while plasmonic MM with metallic rectangular-ring-resonator (M-RR) supports a low-Q electric dipole resonance (ED). The results show that the near-field coupling between the dark TD and bright ED behaves just as that between the two bright modes, which is dependent on the Q factor of the TD resonance. Further, due to the greatly enhanced near-field coupling between the bright ED and dark TD, the coupling distance is significantly extended to about 1.9 times of the wavelength (in media), and robust EIT with large peak value over 0.9 and high Q-factor is achieved. The proposed bilayer MM provides a new EIT platform for design and applications in high-Q cavities, sensing, and slow-light based devices.