Biomedical Applications of Terahertz Spectroscopy and Imaging

A predictive model for MGMT promoter methylation status in glioblastoma based on terahertz spectral data

O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation is a crucial biomarker in glioblastoma (GBM) that influences response to temozolomide. Traditional detection methods, such as gene sequencing, are time-consuming and limited to postoperative analysis. This study explores the use of terahertz time-domain spectroscopy (THz-TDS) combined with machine learning to predict MGMT methylation status intraoperatively. By analyzing 180 GBM tissue samples, a Random Forest model was developed, achieving an AUC of 0.862. The findings suggest that THz spectroscopy offers a rapid, intraoperative alternative to traditional MGMT methylation detection methods, potentially enhancing surgical decision-making and personalized treatment strategies in GBM.

Rapid diagnosis of TERT promoter mutation using Terahertz absorption spectroscopy in glioblastoma

Glioblastoma (GBM) is a highly aggressive brain tumor with poor outcomes and limited treatment options. The telomerase reverse transcriptase (TERT) promoter mutation, one of the key biomarkers in GBM, is linked to tumor progression and prognosis. This study employed terahertz time-domain spectroscopy (THz-TDS) to analyze frozen GBM tissue sections, extracting six spectral features: absorption coefficient, dielectric loss factor, dielectric constant, extinction coefficient, refractive index, and dielectric loss tangent. LASSO regression was employed for feature selection, and then principal component analysis (PCA) was applied to minimize inter-feature correlations. A Random Forest classifier built on these features successfully predicted TERT mutation status, achieving an area under the receiver operating characteristic curve (AUC) of 0.908 in the validation set. Our findings demonstrate that THz spectroscopy, coupled with machine learning, can identify molecular differences associated with TERT mutations, supporting its potential as a rapid, intraoperative diagnostic tool for personalized GBM treatment. This approach could enhance surgical decision-making and optimize patient outcomes through precise, real-time molecular diagnostics.

High-Sensitivity Blood Cell Detection via Terahertz Refractive Index Sensing in Biomedical Applications

Biosensors are essential tools for detecting and analyzing various elements of human biology. This study introduces an innovative circular-shaped photonic crystal fiber (PCF) with a hexahedron core for the precise detection of blood components. The sensor's performance evaluated using COMSOL Multiphysics software. The finite element methods (FEM) is applied to solve Maxwell's equations and perform simulations across a terahertz (THz) frequency range from 1.0 to 3.0 THz. This comprehensive investigation focuses on optimizing several important optical parameters, including relative sensitivity (RS), confinement loss (CL), effective mode area (EMA), and birefringence, etc. for enhancing the detection of various blood components. The Optical sensor is constructed by  Topas as cladding material. The sensor demonstrates exceptional performance with RS of approximately 95.02% for glucose, 95.48% for plasma, 96.30% for white blood cells (WBCs), and 97.04% for red blood cells (RBCs) at an operational frequency of 2.20 THz. Thus the proposed sensor can provide reliable and accurate measurements across different blood components in advanced biomedical applications.

Gold nanoparticle-modified single-walled carbon nanotube terahertz metasurface for ultrasensitive sensing of trace proteins

Research on metasurface sensors with high sensitivity, strong specificity, good biocompatibility and strong integration is the key to promote the application of terahertz waves in the field of biomedical detection. However, traditional metallic terahertz metasurfaces have shortcomings such as poor biocompatibility and large ohmic loss in the terahertz frequency band, impeding their further application and integration in the field of biosensing detection. Here, we overcome this challenge by proposing a high-performance terahertz metasurface based on gold nanoparticles and single-walled carbon nanotubes composite film. Compared with metal materials, carbon nanotubes not only have better biocompatibility, which can reduce the potential adverse reactions between metasurfaces and biological samples, but also have strong tunability in electrical and optical properties. Experimentally, we reveal a method to adjust the dielectric properties of single-walled carbon nanotube films by doping with gold nanoparticles. Leveraging this mechanism, we designed and prepared a single-walled carbon nanotube terahertz metasurface composed of periodically arranged asymmetric open resonant rings. Compared with pure single-walled carbon nanotube films, this device based on a composite single-walled carbon nanotube films have better localized electromagnetic field enhancement characteristics. Through integration with microfluidic channels, this metasurface sensor can achieve direct detection of SAA proteins in solution environments at the fM level. In addition, the device also exhibits a detection sensitivity of 41 GHz/fM. This work has not only made significant progress in the design and function of new high-sensitivity carbon-based terahertz metasurfaces, but also laid the foundation for its application in liquid environment detection of trace biological samples.

Fabrication and application of 3D Terahertz metamaterials with vertical multinanogaps for spectroscopic sensing

Terahertz (THz) metamaterials have garnered attention for their unique electromagnetic properties and potential applications in biomaterial sensing, offering label-free, non-contact capabilities. However, their performance is limited by their diffraction limits, impeding the detection of small objects. This study presents an approach for fabricating three-dimensional (3D) THz metamaterials with vertically oriented, high-aspect-ratio multinanogaps. These 3D metamaterials comprise laminated cross-shaped metal layers, which induce electromagnetic resonance, and polymer layers that support the metal layers at the center of the cross shape. Air nanogaps formed between metal layers achieved aspect ratios of > 64. Conventional microfabrication techniques were employed, including spin coating, metal sputtering deposition, photolithography, ion milling etching, and oxygen plasma etching, without relying on electron beam lithography. Spectroscopic analyses of the fabricated metamaterials revealed that the multilayered structure exhibited a deeper dip than single-layered and double-layered configurations. To validate THz sensing, we used isopropyl alcohol (IPA) for THz spectroscopy applications; the spectra indicated significant peak frequency shifts in the transmission dip of the fabricated device with and without IPA. These findings highlight the application scope of the as-prepared 3D THz metamaterial in material sensing techniques, enhancing THz-metamaterial-based device performance.

Sustainable Materials Enabled Terahertz Functional Devices

Terahertz (THz) devices, owing to their distinctive optical properties, have achieved myriad applications in diverse domains including wireless communication, medical imaging therapy, hazardous substance detection, and environmental governance. Concurrently, to mitigate the environmental impact of electronic waste generated by traditional materials, sustainable materials-based THz functional devices are being explored for further research by taking advantages of their eco-friendliness, cost-effective, enhanced safety, robust biodegradability and biocompatibility. This review focuses on the origins and distinctive biological structures of sustainable materials as well as succinctly elucidates the latest applications in THz functional device fabrication, including wireless communication devices, macromolecule detection sensors, environment monitoring sensors, and biomedical therapeutic devices. We further highlight recent applications of sustainable materials-based THz functional devices in hazardous substance detection, protein-based macromolecule detection, and environmental monitoring. Besides, this review explores the developmental prospects of integrating sustainable materials with THz functional devices, presenting their potential applications in the future.

Identifying phenotypes of colorectal malignant tumors using the quasi-bound state in the continuum of a terahertz metasurface biosensor

A rapid and non-invasive method to identify phenotypes of colorectal malignant tumors is of vital importance for oncological surgery and further development of corresponding anti-tumor drugs. Herein, we demonstrate an approach to detect colorectal adenocarcinoma and colorectal cancer using the quasi-bound state in the continuum (q-BIC) resonance of a metasurface-based terahertz biosensor. We found that the colorectal adenocarcinoma leads to a 40 GHz q-BIC resonance shift compared to healthy colorectal cells. In addition, we found that colorectal cancer results in a q-BIC resonance red-shift of about 60 to 80 GHz. Both colorectal adenocarcinoma and cancer increase the linewidth of q-BIC resonance compared to healthy colorectal cells. The electric permittivity change confirms the aforementioned frequency shift, which is attributed to the water content of different colorectal malignant tumor cells. Our results highlight that the q-BIC resonance of a terahertz photonic biosensor offers a rapid and non-invasive methodology for identifying different colorectal malignant tumors, which accelerates oncological diagnosis.

Hollow-core PCF for terahertz sensing: A new approach for ethanol and benzene detection

Terahertz (THz) spectroscopy is becoming a powerful technique for non-destructive, label-free chemical sensing with applications ranging from medicinal research to security screening. Enhancing THz spectroscopy's sensitivity and selectivity is crucial to maximizing its potential. In this work, we offer a novel optical fiber design, square shape core PCF that is tailored to exploit improved optical features at exterior in the THz region. This analysis suggests that a square shape and three layers with square air apertures for the cladding and core would be ideal. The mathematical analysis is carried out at THz wave dissemination utilizing FEM and boundaries circumstance of the Perfectly Matched Layer. Using the simulation method, the constructed square PCF sensor achieves very high relative sensitivity (94.45%, 94.80%) at 2 THz for two compounds: ethanol (n = 1.354), and benzene (n = 1.36). On the other hand, the low confinement loss (CL) values for the same two compounds at 2 THz are 1.17 ×  10-05 dB/m, and 1.32 ×  1 0-05 dB/m, in that order. We also looked at the potential applications of this special fiber in a variety of fields, including environmental monitoring, chemical sensing, and biomedical diagnostics. The square PCF with square core has hitherto unexplored opportunities for the development of extremely selective and sensitive THz spectroscopic devices with important social consequences in domain of THz perception of chemicals.

Single-Bacterium Diagnosis via Terahertz Near-Field Dielectric Nanoimaging

Single-bacterium diagnostic methods with unprecedented precision and rapid turnaround times are promising tools for facilitating the transition from empirical treatment to personalized anti-infection treatment. Terahertz (THz) radiation, a cutting-edge technology for identifying pathogens, enables the label-free and non-destructive detection of intermolecular vibrational modes and bacterial dielectric properties. However, this individual dielectric property-based detection and the mismatched spatial resolution are limited for the single-bacterium identification of various species of pathogens. Here, we demonstrate a single-bacterium THz dielectric nanoimaging (STDN) strategy by customized THz scattering-type scanning near-field optical microscopy. The THz nanoimages of bacteria are explained and confirmed by theoretical modeling and near-field measurement. By synchronously tracking the bacterial intrinsic dielectric property and extrinsic morphology, the strategy achieved 99.3% and 91.6% accuracy in species identification and antibiotic susceptibility testing with the trained classifier within 2 hours. This proof-of-concept STDN strategy may propel precise bacterial infection management and help to counteract antibiotic resistance.

Vibrational spectra of serotonin by terahertz time domain spectroscopy and DFT simulations

Serotonin is an important biogenic monoamine neurotransmitter that has major influences on mental health disorders; its structural and conformational changes have important roles in the biological functions of the human body. The decreased serotonin levels in the human body are majorly attributed to the causes of anxiety, depressive disorders, mood disorders, etc. Therefore, the quantification of serotonin in our bodies is of utmost importance in unearthing the origin of such physiological disorders. In this study, Terahertz-Time Domain Spectroscopy (THz-TDS) is employed to characterize the unique THz fingerprint of serotonin in the frequency range 0-3 THz. The characteristic THz absorption peaks of serotonin are observed at 0.54, 0.84, and 1.10 THz. In addition, Density Functional Theory (DFT) calculations are performed to investigate the vibrational properties of serotonin. For the vibrational assignment of modes, we have used Potential Energy Distribution (PED) analysis. Furthermore, studies have been conducted on the variation of serotonin concentration in a polyethylene (PE) host medium. The effect of the serotonin concentration in the PE host is studied using the complex refractive index (CRI) model. The sensitivity of detection of serotonin concentration is 0.015 for an increment of 2% concentration in PE medium. This work maps the spectral features of serotonin in the THz range, suggesting that THz-TDS can be used to understand and treat the physiological disorders related to serotonergic systems.

Terahertz scanning near-field optical microscopy for biomedical detection: Recent advances, challenges, and future perspectives

Terahertz (THz) radiation is widely recognized as a non-destructive, label-free, and highly- sensitive tool for biomedical detections. Nevertheless, its application in precision biomedical fields faces challenges due to poor spatial resolution caused by intrinsically long wavelength characteristics. THz scanning near-field optical microscopy (THz-SNOM), which surpasses the Rayleigh criterion, offers micrometer and nanometer-scale spatial resolution, making it possible to perform precise bioinspection with THz imaging. THz-SNOM is attracting considerable attention for its potential in advanced biomedical research and diagnosis. Currently, its family typically includes four members based on distinct principles, which are suitable for different biological applications. This review provides an overview of the principles of these THz-SNOM modalities, outlines their various applications, identifies the obstacles hindering their performance, and envisions their future development.

The theory, technology, and application of terahertz metamaterial biosensors: A review

Terahertz metamaterial biosensors combine terahertz time-domain spectroscopy with metamaterial sensing to provide a sensitive detection platform for a variety of targets, including biological molecules, proteins, cells, and viruses. These biosensors are characterized by their rapid response, sensitivity, non-destructive, label-free operation, minimal sample requirement, and user-friendly design, which also allows for integration with various technical approaches. Advancing beyond traditional biosensors, terahertz metamaterial biosensors facilitate rapid and non-destructive trace detection in biomedical applications, contributing to timely diagnosis and early screening of diseases. In this paper, the theoretical basis and advanced progress of these biosensors are discussed in depth, focusing on three key areas: improving the sensitivity and specificity, and reducing the influence of water absorption in biological samples. This paper also analyzes the potential and future development of these biosensors for expanded applications. It highlights their potential for multi-band tuning, intelligent operations, and flexible, wearable biosensor applications. This review provides a valuable reference for the follow-up research and application of terahertz metamaterial biosensors in the field of biomedical detection.

Rapid, ultrasensitive, and specific RPA-THz system for pathogenic microorganism detection

Pathogenic microorganisms responsible for infectious diseases pose a significant global threat to human health. Existing detection methods, such as qPCR and ELISA, fail to simultaneously meet the requirements for high sensitivity, high specificity, and rapid detection. This study presents an innovative approach for the rapid, specific, and highly sensitive detection of pathogenic microorganisms, particularly Escherichia coli O157:H7 (E. coli O157:H7) and varicella-zoster virus (VZV), by combining recombinase polymerase amplification (RPA) with terahertz time-domain spectroscopy (THz-TDS). The qualitative and quantitative detection method for pathogenic microorganisms was developed and evaluated. The stable and efficient RPA reaction systems were established to specifically amplify the key conserved genes of these pathogens. Then the RPA products were purified, and enriched with MBs. The absorbance spectra were obtained using THz-TDS technology. The linear range of the RPA-THz for detecting E. coli O157:H7 was 0.55 to 5.5 × 104 pg/mL, while for VZV, it was 0.75 to 7.5 × 103 pg/mL. The limit of detection (LOD) for bacteria and viruses was 0.226 pg/mL and 0.528 pg/mL, respectively, demonstrating better sensitivity than the qPCR (550 pg/mL and 750 pg/mL, respectively). In addition, the whole amplification and detection process was completed in about 35 minutes. Compared to traditional pathogen detection techniques, the primary advantage of the developed RPA-THz method exhibited high accuracy, good reproducibility, and short detection times, enabling non-ionizing, label-free analysis for rapid detection with high sensitivity and specificity of pathogenic microorganisms. This study provides a theoretical foundation and practical demonstration for the fast and precise detection of pathogenic microorganisms. It establishes a crucial research basis for further development of RPA-THz sensors, advancing technological progress in the field of food safety, medical diagnostics, environmental monitoring, and public health.

Terahertz Wave Desensitizes Ferroptosis by Inhibiting the Binding of Ferric Ions to the Transferrin

Ferroptosis is a classic type of programmed cell death characterized by iron dependence, which is closely associated with many diseases such as cancer, intestinal ischemic diseases, and nervous system diseases. Transferrin (Tf) is responsible for ferric-ion delivery owing to its natural Fe3+ binding ability and plays a crucial role in ferroptosis. However, Tf is not considered as a classic druggable target for ferroptosis-associated diseases since systemic perturbation of Tf would dramatically disrupt blood iron homeostasis. Here, we reported a nonpharmaceutical, noninvasive, and Tf-targeted electromagnetic intervention technique capable of desensitizing ferroptosis with directivity. First, we revealed that the THz radiation had the ability to significantly decrease binding affinity between the Fe3+ and Tf via molecular dynamics simulations, and the modulation was strongly wavelength-dependent. This result provides theoretical feasibility for the THz modulation-based ferroptosis intervention. Subsequent extracellular and cellular chromogenic activity assays indicated that the THz field at 8.7 μm (i.e., 34.5 THz) inhibited the most Fe3+ bound to the Tf, and the wavelength was in good agreement with the simulated one. Then, functional assays demonstrated that levels of intracellular Fe2+, lipid peroxidation, malondialdehyde (MDA) and cell death were all significantly reduced in cells treated with this 34.5 THz wave. Furthermore, the iron deposition, lipid peroxidation, and MDA in the ferroptosis disease model induced by ischemia-reperfusion injury could be nearly eliminated by the same radiation, validating THz wave-induced desensitization of ferroptosis in vivo. Together, this work provides a preclinical exemplar for electromagnetic irradiation-stimulated desensitization of ferroptosis and predicts an innovative, THz wave-based therapeutic method for ferroptosis-associated diseases in the future.

Monolithic dual-wavelength high-power DFB laser with sub-100 kHz linewidth for THz application

We report an optimized monolithic dual-wavelength distributed feedback (DFB) laser for terahertz (THz) applications, designed to address the challenges of complexity, cost, and power efficiency in a THz transmitter. This laser can achieve a high optical power of 65.93 mW. Under a wide temperature range and high-bias current, the power difference between the two primary modes remains below 1 dB, with each side-mode suppression ratio exceeding 36 dB. Additionally, the two primary modes exhibit low relative intensity noise peaks of -153.88 dB/Hz and -153.46 dB/Hz and narrow linewidths of 117.33 kHz and 70.59 kHz, demonstrating stable and high-performance dual-wavelength operation. These results underscore the potential of the dual-wavelength (DW)-DFB laser as a compact and cost-effective solution for THz systems.

Towards autonomous robotic THz-based in vivo skin sensing: the PicoBot

Terahertz (THz) light has the unique properties of being very sensitive to water, non-ionizing, and having sub-millimeter depth resolution, making it suitable for medical imaging. Skin conditions including eczema, psoriasis and skin cancer affect a high percentage of the population and we have been developing a THz probe to help with their diagnosis, treatment and management. Our in vivo studies have been using a handheld THz probe, but this has been prone to positional errors through sensorimotor perturbations and tremors, giving spatially imprecise measurements and significant variations in contact pressure. As the operator tires through extended device use, these errors are further exacerbated. A robotic system is therefore needed to tune the critical parameters and achieve accurate and repeatable measurements of skin. This paper proposes an autonomous robotic THz acquisition system, the PicoBot, designed for non-invasive diagnosis of healthy and diseased skin conditions, based on hydration levels in the skin. The PicoBot can 3D scan and segment out the region of interest on the skin's surface, precisely position (± 0.5/1 mm/degrees) the probe normal to the surface, and apply a desired amount of force (± 0.1N) to maintain firm contact for the required 60 s during THz data acquisition. The robotic automation improves the stability of the acquired THz signals, reducing the standard deviation of amplitude fluctuations by over a factor of four at 1 THz compared to hand-held mode. We show THz results for skin measurements of volunteers with healthy and dry skin conditions on various parts of the body such as the volar forearm, forehead, cheeks, and hands. The tests conducted validate the preclinical feasibility of the concept along with the robustness and advantages of using the PicoBot, compared to a manual measurement setup.

Terahertz-based biosensors for biomedical applications: A review

Biosensors have many life sciences-related applications, particularly in the healthcare sector. They are employed in a wide range of fields, including drug development, food quality management, early diagnosis of diseases, and environmental monitoring. Terahertz-based biosensing has shown great promise as a label-free, non-invasive, and non-contact method of detecting biological substances. THz Spectroscopy has achieved a remarkable advancement in biomolecule recognition providing a rapid, highly sensitive, and non-destructive approach for various biomedical applications. The significance of THz-based biosensors and the broad spectrum of biomolecules that can be detected and analyzed with biosensors are reviewed in this work. Additionally, this work summarizes several techniques that were previously reported to improve the sensitivity and selectivity of these biosensors. Furthermore, an in-depth comparison between previously developed biosensors with an emphasis on their performance is presented and highlighted in the current review. Lastly, the challenges, the potential, and the future prospects of THz-based biosensing technology are critically addressed.

Thermostable terahertz metasurface enabled by graphene assembly film for plasmon-induced transparency

With the increasing demand on high-density integration and better performance of micro-nano optoelectronic devices, the operation temperatures are expected to significantly increase under some extreme conditions, posing a risk of degradation to metal-based micro-/nano-structured metasurfaces due to their low tolerance to high temperature. Therefore, it is urgent to find new materials with high-conductivity and excellent high-temperature resistance to replace traditional micro-nano metal structures. Herein, we have proposed and fabricated a thermally stable graphene assembly film (GAF), which is calcined at ultra-high temperature (~ 3000 ℃) during the reduction of graphite oxide (GO). Compared with micro-nano metals that usually degrade at around 550 ℃, the proposed GAF maintains a high extent of stability at an extremely high temperature up to 900 ℃. In addition, to make GAF a prime candidate to replace micro-nano metals, we have modified its fabrication process for improving its conductivity to 1.3 × 106 S/m, which is quite close to metals. Thus, micro-nano optoelectronic devices could retain high efficiency even when GAF replaces the crucial micro-nano metals. To verify the thermostability of optoelectronic devices composed of GAF, we have compared the high-temperature resistance performance of two structures capable of achieving plasmon-induced transparency (PIT) at the THz region, one using micro-nano metals (Aluminum) and the other GAF. The Al metasurface displayed a near-complete loss of PIT effects after a high-temperature treatment, while GAF could remain excellent PIT properties at above 900 ℃, thus enable to fulfil its optimum performance. Overall, the proposed thermostable metasurface provides new pathway for the construction of thermostable optoelectronic devices that can operate under ultra-high temperature scenario.

Effect of terahertz radiation on cells and cellular structures

The paper presents the results of modern research on the effects of electromagnetic terahertz radiation in the frequency range 0.5-100 THz at different levels of power density and exposure time on the viability of normal and cancer cells. As an accompanying tool for monitoring the effect of radiation on biological cells and tissues, spectroscopic research methods in the terahertz frequency range are described, and attention is focused on the possibility of using the spectra of interstitial water as a marker of pathological processes. The problem of the safety of terahertz radiation for the human body from the point of view of its effect on the structures and systems of biological cells is also considered.

Cactus-like Metamaterial Structures for Electromagnetically Induced Transparency at THz frequencies

THz metamaterials present unique opportunities for next-generation technologies and applications as they can fill the "THz gap" originating from the weak response of natural materials in this regime, providing a variety of novel or advanced electromagnetic wave control components and systems. Here, we propose a novel metamaterial design made of three-dimensional, metallic, "cactus-like" meta-atoms, showing electromagnetically induced transparency (EIT) and enhanced refractive index sensing performance at low THz frequencies. Following a detailed theoretical analysis, the structure is realized experimentally using multiphoton polymerization and electroless silver plating. The experimental characterization results obtained through THz time domain spectroscopy validate the corresponding numerical data, verifying the high potential of the proposed structure for slow light and sensing applications.

Terahertz Nanoscopy on Low-Dimensional Materials: Toward Ultrafast Physical Phenomena

Low-dimensional materials (LDMs) with unique electromagnetic properties and diverse local phenomena have garnered significant interest, particularly for their low-energy responses within the terahertz (THz) range. Achieving deep subwavelength resolution, THz nanoscopy offers a promising route to investigate LDMs at the nanoscale. Steady-state THz nanoscopy has been demonstrated as a powerful tool for investigating light-matter interactions across boundaries and interfaces, enabling insights into physical phenomena such as localized collective oscillations, quantum confinement of quasiparticles, and metal-to-insulator phase transitions (MITs). However, tracking the ultrafast nonequilibrium dynamics of LDMs remains challenging. Ultrafast THz nanoscopy, with femtosecond temporal resolution, provides a direct pathway to investigate and manipulate the motion of, for example, charges, currents, and carriers at ultrashort time scales. In this review, we focus on recent advances in THz nanoscopy of LDMs, with particular emphasis on the ultrafast dynamics of light-matter interaction. We provide a concise overview of recent advances and suggest future research directions in this impactful field of interdisciplinary science.

Broadband terahertz holography using isotropic VO2 metasurfaces

Vanadium dioxide (VO2) exhibits exceptional phase transition characteristics that enable dynamic manipulation of electromagnetic wave. In this study, a novel design of bilayer isotropic metasurface is introduced. It leverages insulating-to-metallic phase transition of VO2 to enable broadband holography for terahertz wave. For the metallic VO2, the upper VO2 antennas reflect incident terahertz wave and generate hologram. For the insulating VO2, incident wave is reflected by the lower gold antennas and the same hologram is generated with frequency doubling. Working frequencies of the designed holograms are 1.2 THz for metallic VO2 and 1.9 THz for insulating VO2. Due to the broadband performance under each state, the proposed metasurface can achieve holography within 1.0-2.1 THz. It is noteworthy that the generated holograms under two states of VO2 remain entirely independent, and another metasurface that achieves frequency-multiplexed holograms is presented. Our design may have possible applications in holographic display and information encryption.

Integrated identification and detection of hydration state and its evolution using terahertz technology

The accurate detection of dehydration processes in hydrated drugs can reveal various intermolecular vibration modes mediated by hydrogen bonds between water molecules and other components, which underpin the further development of pharmaceutical science, food safety and biophysics. Herein, terahertz (THz) technology is utilized to investigate the dehydration state of d(+)-Raffinose pentahydrate (Rf·5H2O), in conjunction with imaging-based point by point scanning data acquisition and barcodes methods, to establish an innovative platform integrated identification, trace detection, and application capabilities. Our study demonstrates that the dehydration process of Rf·5H2O can be dynamically monitored through the evolution of its THz absorption peaks, offering more precise results compared to XRD and Raman spectroscopies. Moreover, the absorbance spectra data collected at each individual pixel is utilized to build visualized THz images, achieving an ultralow minimum content required for detection of 0.032 μg/(50 μm)2. Additionally, we introduce a THz spectra-barcode conversion system that not only ensures efficient electronic recordkeeping but also enhances user readability, thereby facilitating the practical applications of THz technology.

Research Advances in Terahertz Technology for Skin Detection

Background: With the continuous development of Terahertz technology and its high sensitivity to water, Terahertz technology has been widely applied in various research areas within the field of biomedicine, such as research onskin wounds and burns, demonstrating numerous advantages and potential. Objective: The aim of this study is to summarize and conclude the current research status of Terahertz radiation in skin wounds, burns, and melanoma. Additionally, it seeks toreveal the development status of Terahertz in skin wound models and analyze the short comings of Terahertz in detecting such models at the present stage. Methods: We retrieved relevant literature published from the inception of the Web of Science and CNKI databases up to 2024. The search terms included "THz," "Terahertz," "skin," "wound," "burn," and "melanoma." High-quality articles were included after rigorous screening. Results and Conclusions: This review explores the progress of terahertz radiation technology in the treatment and diagnosis of skin wounds and other related diseases. The results of its interaction with skin tissues provide valuable insights for future research. Terahertz radiation imaging has proven to be effective in assessing burn severity, capturing changes in edema, measuring exudates in dressings, assisting in burn grading and detection, and quantifying wound changes over time. Terahertz technology offers significant advantages in trauma assessment, which has accelerated its development and adoption in this field. (4) However, fs-THz radiation has been found to have the potential drawback of affecting wound healing. This finding necessitates careful consideration before application, and further research is warranted to explore its role in burn assessment and other medical applications.

The Use of Terahertz Computed Tomography and Time Domain Spectroscopy to Evaluate Symmetry in 3D Printed Parts

3D printing has become essential to many fields for its low-cost production and rapid prototyping abilities. As 3D printing becomes an alternative manufacturing tool, developing methods to non-destructively evaluate defects for quality control is essential. This study integrates the non-destructive terahertz (THz) analysis methods of terahertz time-domain spectroscopy (THz-TDS) and terahertz computed tomography (THz CT) to image and assess 3D printed resin structures for defects. The terahertz images were reconstructed using MATLAB, and the rotational symmetry of various structures before and after the introduction of defects was evaluated by calculating the mean squared deviation (MSD), which served as a symmetry parameter to indicate the presence of defects. Structures A and B had MSD values that were at least three standard deviations larger after introducing defects to their structures, showing a significant change in symmetry and indicating the existence of defects. Similarly, in structure C, blockages in parts made with different post-cures were identified based on the increase in MSD values for those slices. For structure D, the presence of a defect increased the MSD value by 14%. The results of this study verify that the MSD calculated for the rotational symmetry of the structures was greater when defects were present, accurately reflecting the anticipated breaks in symmetry. This paper demonstrates that terahertz imaging, combined with MSD analysis, is a viable procedure to identify and quantify defects in rotationally symmetric 3D printed structures.

A Reflective Terahertz Point Source Meta-Sensor with Asymmetric Meta-Atoms for High-Sensitivity Bio-Sensing

Biosensors operating in the terahertz (THz) region are gaining substantial interest in biomedical analysis due to their significant potential for high-sensitivity trace-amount solution detection. However, progress in compact, high-sensitivity chips and methods for simple, rapid and trace-level measurements is limited by the spatial resolution of THz waves and their strong absorption in polar solvents. In this work, a compact nonlinear optical crystal (NLOC)-based reflective THz biosensor with a few arrays of asymmetrical meta-atoms was developed. A near-field point THz source was locally generated at a femtosecond-laser-irradiation spot via optical rectification, exciting only the single central meta-atom, thereby inducing Fano resonance. The reflective resonance response demonstrated dependence on several aspects, including structure asymmetricity, geometrical size, excitation point position, thickness and array-period arrangement. DNA samples were examined using 1 μL applied to an effective sensing area of 0.234 mm2 (484 μm × 484 μm) for performance evaluation. The developed Fano resonance sensor exhibited nearly double sensitivity compared to that of symmetrical sensors and one-gap split ring resonators. Thus, this study advances liquid-based sensing by enabling easy, rapid and trace-level measurements while also driving the development of compact and highly sensitive THz sensors for biological samples.

Terahertz-based optoelectronic properties of ZnS quantum dot-polymer composites: For device applications

Terahertz (THz) technology integration with nanomaterials is receiving excellent attention for next-generation applications, including enhanced imaging and communication. The excellent optical properties in THz domain can lead to preparation of low-cost CMOS camera which can convert THz radiation into optical signal in very efficient manner. In the present study, we have studied the properties of Zinc Sulfide quantum dots (ZnS QDs) embedded with Polyvinyl Alcohol (PVA) composites films using THz Signal at room temperature. The optical characterizations such as refractive index, absorption coefficients and dielectric constants of these samples were measured in the 0.1-2.0 THz range. Additionally, optical impedance, surface roughness, and reflection coefficient in TE and TM mode between 0.1 and 2.0 THz range were determined for these samples based on surface roughness-based reflection and scattering properties. The surface roughness factor was used to measure the optical impedance of the ZnS QDs based polymer films. The measured values of the absorption coefficient at 266 nm are compared with THz radiation, and the refractive indices of these samples range from 1.75 to 2.0. Finally, these samples were subjected to UV light excitation (λexe = 266 nm) of 0.15 ns duration and 400 nm for the fluorescence and corresponding life time measurements. We observed two numbers of fluorescence lines in nanosecond based excited domain whereas 400 nm excitation-based fluorescence life time lies between 13.8-11.39 ns range along with shift in fluorescence lines between 538.7 to 560.7 nm, respectively.

The Transcriptomic Response of Cells of the Thermophilic Bacterium Geobacillus icigianus to Terahertz Irradiation

As areas of application of terahertz (THz) radiation expand in science and practice, evidence is accumulating that this type of radiation can affect not only biological molecules directly, but also cellular processes as a whole. In this study, the transcriptome in cells of the thermophilic bacterium Geobacillus icigianus was analyzed immediately after THz irradiation (0.23 W/cm2, 130 μm, 15 min) and at 10 min after its completion. THz irradiation does not affect the activity of heat shock protein genes and diminishes the activity of genes whose products are involved in peptidoglycan recycling, participate in redox reactions, and protect DNA and proteins from damage, including genes of chaperone protein ClpB and of DNA repair protein RadA, as well as genes of catalase and kinase McsB. Gene systems responsible for the homeostasis of transition metals (copper, iron, and zinc) proved to be the most sensitive to THz irradiation; downregulation of these systems increased significantly 10 min after the end of the irradiation. It was also hypothesized that some negative effects of THz radiation on metabolism in G. icigianus cells are related to disturbances in activities of gene systems controlled by metal-sensitive transcription factors.

Detection of optical properties of chiral substances by a photoconductive THz polarization detector

Chiral enantiomers have significant differences in biochemical functions. The use of THz wave polarization detection to characterize the optical properties of chiral substances is of great significance to the development of life science and the identification and application of chiral substances. However, the traditional polarization detection procedures of THz waves are complex, which limits the study of chiral substances. Herein, we proposed a high-sensitivity THz polarization detector, which can simultaneously obtain the change information of amplitude, phase, and polarization state through a single measurement. The optical rotation and elliptical angle of solid and liquid D/L-Glutamic acid 5-methyl ester in the THz band are studied. Then it is verified that anisotropic interference may occur in the preparation of solid samples. Finally, the effects of sample content and thickness on polarization are obtained. The experimental results show that different chirality has the opposite effect on the state of polarization, and the difference between chiral enantiomers can be detected by this method. This work is of great significance for understanding the optical properties of chiral substances and promoting the development of chiral recognition.

Unveiling enamel demineralization mechanisms by sensitive dielectric differentiation based on terahertz nanospectroscopy

The early stage of dental caries, i.e. demineralization, has always been a topic of concern to dentists. Understanding the essential mechanism of its occurrence is of great significance for the prevention and treatment of dental caries. However, owing to limitations in resolution and the detection capabilities of diagnostic tools, the study of enamel demineralization has always been a challenge. Terahertz (THz) technology, especially the combination of scanning near-field optical microscopy (s-SNOM) and THz time-domain spectroscopy (TDS), due to its nanoscale resolution, has shown great advantages in the field of biological imaging. Here, a THz s-SNOM system is used to perform near-field imaging of enamel before and after demineralization at the nanoscale. It can be found that near-field signals decrease significantly after demineralization. This is due to the changes of the crystal lattice and the transfer of mineral ions during demineralization, which leads to a decrease in the permittivity of the enamel. The novel approach in this study reveals the essence of demineralization and lays the groundwork for additional research and potential interventions.

Imaging-based terahertz pixelated metamaterials for molecular fingerprint sensing

With the rapid development of terahertz-enabled devices, the study of miniaturized and integrated systems has attracted significant attention. We experimentally demonstrate an imaging-based pixelated metamaterial for detecting terahertz molecular fingerprints related to intermolecular vibrations and large-amplitude intramolecular modes, including chemical identification and compositional analysis. The compact THz sensor consists of a 4 × 4 pixelated filter-detector array with transmission resonances tuned to discrete frequencies. The absorption spectra of analytes are computationally reconstructed from different spectral responses of meta-pixels, and the resulting information is characterized via near-field imaging. Due to the spectrometer-less operation principle, such imaging-based approaches provide an alternative method for developing sensitive, versatile, and miniaturized THz biosensors, especially for practical field deployment applications.

Statistical Analysis of Gastric Cancer Cells Response to Broadband Terahertz Radiation with and without Contrast Nanoparticles

The paper describes the statistical analysis of the response of gastric cancer cells and normal cells to broadband terahertz radiation up to 4 THz, both with and without the use of nanostructured contrast agents. The THz spectroscopy analysis was comparatively performed under the ATR procedure and transmission measurement procedure. The statistical analysis was conducted towards multiple pairwise comparisons, including a support medium (without cells) versus a support medium with nanoparticles, normal cells versus normal cells with nanoparticles, and, respectively, tumor cells versus tumor cells with nanoparticles. When generally comparing the ATR procedure and transmission measurement procedure for a broader frequency domain, the differentiation between normal and tumor cells in the presence of contrast agents is superior when using the ATR procedure. THz contrast enhancement by using contrast agents derived from MRI-related contrast agents leads to only limited benefits and only for narrow THz frequency ranges, a disadvantage for THz medical imaging.

Stretchable Dual-Axis Terahertz Bifocal Metalens with Flexibly Polarization-Dependent Focal Position and Direction

Varifocal lenses are essential components in any optical system, while traditional lenses suffer from bulky volume, fixed focal position, and limited working spectra. As well-arranged subwavelength structures, metalenses overcome the abovementioned obstacles and exhibit merits of ultrathin thickness, flexible focal length, and multifocus. The electromagnetic responses of metasurfaces, including metalens, rely on the phase distributions of phase-shifting elements. The steerable focal direction is investigated to obtain the combinations of focusing and anomalous refraction phase distribution. To fully explore the flexibility of focal length and direction, seven designs of double layers of terahertz (THz) bifocal metalenses are proposed and investigated in this study. They exhibit dependent and independent relationships of tunable focal length and direction with flexible tuning mechanisms. Along with polarization multiplexing, two different focuses can be obtained when the incident waves are x-linear and y-linear polarization states, respectively. The simulation results agreed well with the theoretical predictions. These designs provide a new method to modulate the focal position precisely with promising applications in wireless communication, imaging, and on-chip optical integration systems.

Transdermal Sensing of Enzyme Biomarker Enabled by Chemo-Responsive Probe-Modified Epidermal Microneedle Patch in Human Skin Tissue

Wearable bioelectronics represents a significant breakthrough in healthcare settings, particularly in (bio)sensing which offers an alternative way to track individual health for diagnostics and therapy. However, there has been no notable improvement in the field of cancer, particularly for skin cancer. Here, a wearable bioelectronic patch is established for transdermal sensing of the melanoma biomarker, tyrosinase (Tyr), using a microneedle array integrated with a surface-bound chemo-responsive smart probe to enable target-specific electrochemical detection of Tyr directly from human skin tissue. The results presented herein demonstrate the feasibility of a transdermal microneedle sensor for direct quantification of enzyme biomarkers in an ex vivo skin model. Initial performance analysis of the transdermal microneedle sensor proves that the designed methodology can be an alternative for fast and reliable diagnosis of melanoma and the evaluation of skin moles. The innovative approach presented here may revolutionize the landscape of skin monitoring by offering a nondisruptive means for continuous surveillance and timely intervention of skin anomalies, such as inflammatory skin diseases or allergies and can be extended to the screening of multiple responses of complementary biomarkers with simple modification in device design.

Membrane-mediated modulation of mitochondrial physiology by terahertz waves

Extensive studies have demonstrated the diverse impacts of electromagnetic waves at gigahertz and terahertz (THz) frequencies on cytoplasmic membrane properties. However, there is little evidence of these impacts on intracellular membranes, particularly mitochondrial membranes crucial for mitochondrial physiology. In this study, human neuroblast-like cells were exposed to continuous 0.1 THz radiation at an average power density of 33 mW/cm2. The analysis revealed that THz exposure significantly altered the mitochondrial ultrastructure. THz waves enhanced the enzymatic activity of the mitochondrial respiratory chain but disrupted supercomplex assembly, compromising mitochondrial respiration. Molecular dynamics simulations revealed altered rates of change in the quantity of hydrogen bonds and infiltration of water molecules in lipid bilayers containing cardiolipin, indicating the specific behavior of cardiolipin, a signature phospholipid in mitochondria, under THz exposure. These findings suggest that THz radiation can significantly alter mitochondrial membrane properties, impacting mitochondrial physiology through a mechanism related to mitochondrial membrane, and provide deeper insight into the bioeffects of THz radiation.

Terahertz s-SNOM Imaging of a Single Cell with Nanoscale Resolution

Terahertz scattering scanning near-field optical microscopy is a robust spectral detection technique with a nanoscale resolution. However, there are still major challenges in investigating the heterogeneity of cell membrane components in individual cells. Here, we present a novel and comprehensive analytical approach for detecting and investigating heterogeneity in cell membrane components at the single-cell level. In comparison to the resolution of the topographical atomic force microscopy image, the spatial resolution of the terahertz near-field amplitude image is 3 times that of the former. This ultrafine resolution enables the compositional distribution in the cell membrane, such as the distribution of extracellular vesicles, to be finely characterized. Furthermore, via extraction of the near-field absorption images at specific frequencies, the visualization and compositional difference analysis of cell membrane components can be presented in detail. These findings have significant implications for the intuitive and visual analysis of cell development and disease evolutionary pathways.

Observation of THz surface waves escaping from metal gratings through a dielectric substrate

Extensive research has been conducted on generating THz waves using Smith-Purcell radiation, yet a portion of the electron bunch's interaction energy with the gratings is confined to the metal gratings' surface, leading to a low THz radiation power. This paper experimentally demonstrates that metal gratings with a dielectric substrate can emit the resonant modes in surface waves when excited by relativistic femtosecond electron bunches. The observed spectra of the resonant THz waves align well with the theoretical estimations derived from the configuration's dispersion relation and 3D simulations. In comparison to traditional Smith-Purcell radiation generated by the grating, these resonant THz waves exhibit significantly higher intensity and improved orientation. Additionally, we investigated the radiation characteristics of the resonant THz waves, including radiation angle, beam-grating distance, beam energy, and bunch length. This innovative approach presents a novel method for generating high-power coherent terahertz radiation.

Optical Tweezing Terahertz Probing for a Single Metal Nanoparticle

Recently, extensive research has been reported on the detection of metal nanoparticles using terahertz waves, due to their potential for efficient and nondestructive detection of chemical and biological samples without labeling. Resonant terahertz nanoantennas can be used to detect a small amount of molecules whose vibrational modes are in the terahertz frequency range with high sensitivity. However, the positioning of target molecules is critical to obtaining a reasonable signal because the field distribution is inhomogeneous over the antenna structure. Here, we combine an optical tweezing technique and terahertz spectroscopy based on nanoplasmonics, resulting in extensive controllable tweezing and sensitive detection at the same time. We observed optical tweezing of a gold nanoparticle and detected it with terahertz waves by using a single bowtie nanoantenna. Furthermore, the calculations confirm that molecular fingerprinting is possible by using our technique. This study will be a prestep of biomolecular detection using gold nanoparticles in terahertz spectroscopy.

Characteristic fingerprint spectrum of α-synuclein mutants on terahertz time-domain spectroscopy

α-Synuclein, a presynaptic neuronal protein encoded by the SNCA gene, is involved in the pathogenesis of Parkinson's disease. Point mutations and multiplications of α-synuclein (A30P and A53T) are correlated with early-onset Parkinson's disease characterized by rapid progression and poor prognosis. Currently, the clinical identification of SNCA variants, especially disease-related A30P and A53T mutants, remains challenging and also time consuming. This study aimed to develop a novel label-free detection method for distinguishing the SNCA mutants using transmission terahertz (THz) time-domain spectroscopy. The protein was spin-coated onto the quartz to form a thin film, which was measured using THz time-domain spectroscopy. The spectral characteristics of THz broadband pulse waves of α-synuclein protein variants (SNCA wild type, A30P, and A53T) at different frequencies were analyzed via Fourier transform. The amplitude A intensity (AWT, AA30P, and AA53T) and peak occurrence time in THz time-domain spectroscopy sensitively distinguished the three protein variants. The phase φ difference in THz frequency domain followed the trend of φWT > φA30P > φA53T. There was a significant difference in THz frequency amplitude A' corresponding to the frequency ranging from 0.4 to 0.66 THz (A'A53T > A'A30P > A'WT). At a frequency of 0.4-0.6 THz, the transmission T of THz waves distinguished three variants (TA53T > TA30P > TWT), whereas there was no difference in the transmission T at 0.66 THz. The SNCA wild-type protein and two mutant variants (A30P and A53T) had distinct characteristic fingerprint spectra on THz time-domain spectroscopy. This novel label-free detection method has great potential for the differential diagnosis of Parkinson's disease subtypes.

A Terahertz Metasurface Sensor Based on Quasi-BIC for Detection of Additives in Infant Formula

Prohibited additives in infant formula severely affect the health of infants. Terahertz (THz) spectroscopy has enormous application potential in analyte detection due to its rich fingerprint information content. However, there is limited research on the mixtures of multiple analytes. In this study, we propose a split ring metasurface that supports magnetic dipole bound states in the continuum (BIC). By breaking the symmetry, quasi-BIC with a high quality (Q) factor can be generated. Utilizing an angle-scanning strategy, the frequency of the resonance dip can be shifted, resulting in the plotting of an envelope curve which can reflect the molecular fingerprint of the analytes. Two prohibited additives found in infant formula, melamine and vanillin, can be identified in different proportions. Furthermore, a metric similar to the resolution in chromatographic analysis is introduced and calculated to be 0.61, indicating that these two additives can be detected simultaneously. Our research provides a new solution for detecting additives in infant formula.

Highly integrated automatic injection terahertz microfluidic biosensor based on metasurface and LT-GaAs photoconductive antenna

In this paper, a highly integrated terahertz (THz) biosensor is proposed and implemented, which pioneered the preparation of low-temperature gallium arsenide (LT-GaAs) thin film photoconductive antenna (PCA) on the sensor for direct generation and detection of THz waves, simplifying complex terahertz time-domain spectroscopy (THz-TDS) systems. A latch type metasurface is deposited in the detection region to produce a resonance absorption peak at 0.6 THz that is independent of polarisation. Microfluidics is utilised and automatic injection is incorporated to mitigate the experimental effects of hydrogen bond absorption of THz waves in aqueous-based environment. Additionally, cell damage is minimised by regulating the cell flow rate. The biosensor was utilised to detect the concentration of three distinct sizes of bacteria with successful results. The assay was executed as a proof of concept to detect two distinct types of breast cancer cells. Based on the experimental findings, it has been observed that the amplitude and blueshift of the resonance absorption peaks have the ability to identify and differentiate various cancer cell types. The findings of this study introduce a novel approach for developing microfluidic THz metasurface biosensors that possess exceptional levels of integration, sensitivity, and rapid label-free detection capabilities.

Metal-Graphene Hybrid Terahertz Metasurfaces for Circulating Tumor DNA Detection Based on Dual Signal Amplification

Terahertz (THz) spectroscopy has impressive capability for label-free biosensing, but its utility in clinical laboratories is rarely reported due to often unsatisfactory detection performances. Here, we fabricated metal-graphene hybrid THz metasurfaces (MSs) for the sensitive and enzyme-free detection of circulating tumor DNA (ctDNA) in pancreatic cancer plasma samples. The feasibility and mechanism of the enhanced effects of a graphene bridge across the MS and amplified by gold nanoparticles (AuNPs) were investigated experimentally and theoretically. The AuNPs serve to boost charge injection in the graphene film and result in producing a remarkable change in the graded transmissivity index to THz radiation of the MS resonators. Assay design utilizes this feature and a cascade hybridization chain reaction initiated on magnetic beads in the presence of target ctDNA to achieve dual signal amplification (chemical and optical). In addition to demonstrating subfemtomolar detection sensitivity and single-nucleotide mismatch selectivity, the proposed method showed remarkable capability to discriminate between pancreatic cancer patients and healthy individuals by recognizing and quantifying targeted ctDNAs. The introduction of graphene to the metasurface produces an improved sensitivity of 2 orders of magnitude for ctDNA detection. This is the first study to report the combined application of graphene and AuNPs in biosensing by THz spectroscopic resonators and provides a combined identification scheme to detect and discriminate different biological analytes, including nucleic acids, proteins, and various biomarkers.

Ultrafast snapshots of terahertz electric potentials across ring-shaped quantum barriers

Probing the time evolution of the terahertz electric field within subwavelength dimensions plays a crucial role in observing the nanoscale lightwave interactions with fundamental excitations in condensed-matter systems and in artificial structures, such as metamaterials. Here, we propose a novel probing method for measuring terahertz electric potentials across nanogaps using a combination of optical and terahertz pulse excitations. To achieve this, we employ ring-shaped nanogaps that enclose a metallic island, allowing us to capture tunneling charges when subjected to terahertz electromagnetic pulse illumination. By controlling and manipulating the terahertz tunneling charges through a focused optical gate pulse, we can obtain the terahertz potential strength as a function of spatial coordinates and time delays between pulses. To accurately quantify the time evolution of terahertz electric potential across quantum barriers, we carefully calibrate the recorded nonlinear tunneling current. Its on-resonance and off-resonance behaviors are also discussed, providing valuable insights into the antenna's characteristics and performance.

Terahertz stretchable metamaterials with deformable dolmen resonators for uniaxial strain measurement

In this study, we propose a terahertz stretchable metamaterial that can measure uniaxial strain. Gold dolmen resonators formed on a sheet of polydimethylsiloxane (PDMS) is deformed by strain, and its resonance peak exhibits the gradual decrease in reflectance without a frequency shift, which is suitable for imaging applications at a single frequency. The metamaterial was designed by mechanical and electromagnetic simulations and fabricated by microfabrication including a transfer process of gold structures from a glass substrate to a PDMS sheet. By measuring the reflectance and observing the deformation under different strains, the reflectance decrease was obtained at 0.292 THz despite the appearance of wrinkles on gold structures. Linear response and repeatability up to 20% strain were also confirmed. Furthermore, the strain measurement through a sheet of paper was demonstrated, suggesting that our method can be applied even in situations where opaque obstacles in the visible region exist.

Terahertz in vivo imaging of human skin: Toward detection of abnormal skin pathologies

Terahertz (THz) imaging has long held promise for skin cancer detection but has been hampered by the lack of practical technological implementation. In this article, we introduce a technique for discriminating several skin pathologies using a coherent THz confocal system based on a THz quantum cascade laser. High resolution in vivo THz images (with diffraction limited to the order of 100 μm) of several different lesion types were acquired and compared against one another using the amplitude and phase values. Our system successfully separated pathologies using a combination of phase and amplitude information and their respective surface textures. The large scan field (50 × 40 mm) of the system allows macroscopic visualization of several skin lesions in a single frame. Utilizing THz imaging for dermatological assessment of skin lesions offers substantial additional diagnostic value for clinicians. THz images contain information complementary to the information contained in the conventional digital images.

High-precision sensor for glucose solution using active multidimensional feature THz spectroscopy

Terahertz waves are known for their bio-safety and spectral fingerprinting features, and terahertz spectroscopy technology holds great potential for both qualitative and quantitative identification in the biomedical field. There has been a substantial amount of research utilizing this technology in conjunction with machine learning algorithms for substance identification. However, due to the strong absorption of water for terahertz waves, the single-dimensional features of the sample become indistinct, thereby diminishing the efficiency of the algorithmic recognition. Building upon this, we propose a method that employs terahertz time-domain spectroscopy (THz-TDS) in conjunction with multidimensional feature spectrum identification for the detection of blood sugar and glucose mixtures. Our research indicates that combining THz-TDS with multidimensional feature spectrum and linear discriminant analysis (LDA) algorithms can effectively identify glucose concentrations and detect adulteration. By integrating the multidimensional feature spectrum, the identification success rate increased from 68.9% to 96.0%. This method offers an economical, rapid, and safe alternative to traditional methods and can be applied in blood sugar monitoring, sweetness assessment, and food safety.

Super-resolution terahertz imaging based on a meta-waveguide

A terahertz metamaterial waveguide (meta-waveguide) and a meta-waveguide-based lens-free imaging system are presented. The meta-waveguide not only inherits the low-loss transmission performance of a waveguide but also breaks through the diffraction limit under the action of the metamaterial, achieving subwavelength focusing. The focusing distance is far greater than the Rayleigh length, thus enabling far-field scanning imaging. For verification, a metal ring-based meta-waveguide was fabricated by 3D printing and metal cladding technology. Then, a transmission scanning imaging system working at 0.1 THz was built. High quality terahertz images with a resolution of 1/3 of the wavelength were obtained by placing the imaging targets at the focus and performing two-dimensional scanning. The focusing and transmission of terahertz wave in the meta-waveguide were simulated and analyzed.

Terahertz 3-D fast line-scanning imaging using 3-D printed devices

This article presents a terahertz (THz) fast line-scanning imaging system with three-dimensional (3-D) focus-steering capability operating at 0.1 THz. The system comprises a 3-D printed rotating multi-prism plate and a dual-device structure consisting of a negative ridge pyramid and a column ridge pyramid. The simulation and experimental results demonstrate that the system generates a sheet-shaped diffraction-free beam with a projection distance of approximately 175 mm and a diffraction-free distance of approximately 200 mm. Moreover, the system maintains a resolution greater than 4 mm within the diffraction-free range. Furthermore, the proposed THz lens-less line-scanning imaging system enables 3-D scanning imaging within a set range of ±22°. The proposed approach can be extended to cover other frequencies within the THz range by appropriately adjusting the parameters. The system has the advantages of long working distance and long depth of field, making it a very attractive candidate for low-cost, easy-fabrication, and easy-adjustment solutions for the next generation of THz fast detection and imaging technology.

A hybrid quantum-classical theory for predicting terahertz charge-transfer plasmons in metal nanoparticles on graphene

Metal nanoparticle (NP) complexes lying on a single-layer graphene surface are studied with a developed original hybrid quantum-classical theory using the Finite Element Method (FEM) that is computationally cheap. Our theory is based on the motivated assumption that the carrier charge density in the doped graphene does not vary significantly during the plasmon oscillations. Charge transfer plasmon (CTP) frequencies, eigenvectors, quality factors, energy loss in the NPs and in graphene, and the absorption power are aspects that are theoretically studied and numerically calculated. It is shown the CTP frequencies reside in the terahertz range and can be represented as a product of two factors: the Fermi level of graphene and the geometry of the NP complex. The energy losses in the NPs are predicted to be inversely dependent on the radius R of the nanoparticle, while the loss in graphene is proportional to R and the interparticle distance. The CTP quality factors are predicted to be in the range ∼10-100. The absorption power under CTP excitation is proportional to the scalar product of the CTP dipole moment and the external electromagnetic field. The developed theory makes it possible to simulate different properties of CTPs 3-4 orders of magnitude faster compared to the original FEM or the finite-difference time domain method, providing possibilities for predicting the plasmonic properties of very large systems for different applications.

Fano resonance-integrated metal nanoparticles' enhanced sensing for pesticide detection

The combined application of metasurface and terahertz (THz) time-domain spectroscopy techniques has received considerable attention in the fields of sensing and detection. However, to detect trace samples, the THz wave must still be enhanced locally using certain methods to improve the detection sensitivity. In this study, we proposed and experimentally demonstrated a fano resonance metasurface-based silver nanoparticles (FaMs-AgNPs) sensor. AgNPs can enhance the sensitivity of the sensor by generating charge accumulation and inducing localized electric field enhancement through the tip effect, thereby enhancing the interaction between the THz waves and analytes. We investigated the effects of four different contents of AgNPs, 10 µl, 20 µl, 30 µl and 40 µl, on the detection of acetamiprid. At 30 µl of AgNPs, the amplitude change of the FaMs-AgNPs sensor was more pronounced and the sensitivity was higher, which could detect acetamiprid solutions as low as 100 pg/ml. The FaMs-AgNPs sensor has the advantages of a simple structure, easy processing, and excellent sensing performance, and has a great potential application value in the field of THz trace detection and other fields.