Current dielectric modelling of corneal tissue in the terahertz (THz) range relies on binary free water and collagen mixtures using effective media theories despite evidence that bound water significantly impacts THz measurements. No comprehensive theory exists for modelling the dielectric response of tropocollagen, the native state of collagen type-1 that constitutes approximately 90% of the corneal stroma. This work estimates the proportions of different water compartments in corneal stroma based on biophysical research on water-binding structures in type-1 collagen tendons. Our calculations indicate that at physiological hydration levels (78%), more than half of the water content exists in bound states rather than as free water. We discuss how these distinct water compartments contribute differently to dielectric properties in the THz range, establishing a foundation for more accurate finite-difference time-domain (FDTD) simulations to assess the potential of THz pulsed imaging for direct corneal hydration assessment.

Interrelated secondary events occur within days and weeks following a spinal cord injury (SCI), constituting a major hurdle in providing both an effective and affordable treatment for spinal cord repair in that it requires a multifaceted approach. Photobiomodulation (PBM) therapy in the red/near‐infrared spectrum holds promising reparative potential; however, there are no consistent or defined parameters for PBM delivery, which may explain the limited number of ongoing clinical trials and less‐than‐optimal reported outcomes. This review outlines the associated complexities of the secondary cascade after SCI, with insights on how and when red/near‐infrared irradiation may alleviate these issues. The primary focus is to discuss limitations within the field that may be inhibiting our ability to characterize optimal guidelines and specifications. Ultimately, this review provides a call for action, as there is an urgent need for consensus and standardization of therapeutic preclinical methodologies if we hope to develop treatment protocols that provide a first‐line minimally invasive therapy to (i) minimize injury sequelae and (ii) facilitate spinal cord repair. We recommend establishing a universal method to measure the therapeutic dose of light delivered to an injury site and employing standardized methodologies across all studies to assess the benefits of PBM therapy.

Millimeter wave (MMW) radiation from 30-300 GHz induces biological effects beyond thermal heating, affecting gene expression, neuronal function, intracellular signaling, and cellular structure. This study investigated MMW-specific effects on neuronal membranes using the lipophilic fluorescent probe HEDAF to visualize membrane properties in intact leech ganglia during 60 GHz MMW exposure. Despite continuous temperature increase to approximately 6.2±0.5°C above baseline, fluorescence imaging revealed non-linear, phasic changes in membrane fluorescence during the initial 15-20 seconds of exposure. Two distinct response patterns were observed: "S-shaped" and "V-shaped" fluorescence trajectories, neither following the monotonic temperature profile. These patterns suggest that MMW radiation induces specific alterations to membrane properties, including changes in lipid mobility, local pH shifts, or reorganization of membrane components. A comparison with thermal-only controls confirms that these effects are distinct from conventional heating responses. Our findings provide direct visualization of MMW-specific membrane dynamics in neuronal tissue, contributing to our understanding of non-thermal biological mechanisms of MMW radiation that have implications for emerging wireless technologies and potential therapeutic applications.

This study demonstrates the use of terahertz pulsed imaging (TPI) to detect sub-resolution delamination indirectly by monitoring time-of-flight shifts through a 2 mm quartz window. The window is placed on a metal step wedge with 10–90 µm steps simulated air gaps beneath the window. While the quartz–air interface reflection was not resolvable, increasing step depths produced a clear shift in the second reflected pulse (from the quartz–metal interface), corresponding to increased apparent thickness of the window. Notably, even a 10 µm air gap resulted in a measurable change in the calculated quartz thickness, demonstrating the method’s sensitivity to delamination layers below the system’s axial resolution, defined as the minimum layer thickness (dmin) that can be resolved based on the temporal separation between two reflected pulses. These results support the potential of TPI as a non-destructive technique for early-stage defect detection in protective coatings, e.g. anti-corrosion paints.

Adhesive failure leading to delamination in anti-corrosion coating systems compromises structural integrity by creating thin gaps that allow the ingress of corrosive agents like water. This study investigates the capability of terahertz pulsed imaging to detect air gaps thinner than a THz system's minimum resolvable thickness by measuring apparent thickness changes in overlaying layers. The minimum resolvable thickness in terahertz pulsed imaging, referred to as the axial resolution, is determined by the system's bandwidth. To test this approach, THz measurements were conducted on a 2 mm thick quartz window positioned above a metal substrate with an intervening 19 [Formula: see text]m air gap. An increase in the apparent thickness of the quartz window was observed, consistent with theoretical expectations, despite the air gap being undetectable as a distinct reflection. This analysis was extended to multi-layered paint systems consisting of top, mid, and base coatings on steel plates. Cyclic ageing induced a delamination layer between the metal substrate and base coating, estimated to be 10 [Formula: see text]m by scanning electron microscopy. Terahertz pulsed imaging analysis showed a corresponding 9.9-13.1 [Formula: see text]m increase in the apparent base coating thickness, consistent with the quartz window results. These findings demonstrate that terahertz pulsed imaging offers a non-destructive method for identifying sub-resolution air gaps, enabling early-stage detection of delamination in protective coatings.

Guanosine monophosphate (GMP) is a nucleotide that can self-assemble in aqueous solution under certain conditions. An understanding of the process at the molecular level is an essential step to comprehend the involvement of DNA substructures in transcription and replication, as well as their relationship to genetic diseases such as cancer. We present the temperature-dependent terahertz (1.5-12 THz, 50-400 cm-1) absorptivity spectra of aqueous Na2 GMP solution in comparison with the aqueous solutions of other RNA nucleotides. Distinct absorption features were observed in the spectrum of GMP, which we attribute to the intramolecular modes of the self-assemblies (i.e., G-complexes) that, at 1 M, start to form at 313 K and below. Changes in broad-band features of the terahertz spectrum were also observed, which we associate with the release of hydration water in the temperature-dependent formation of guanine quadruplexes. Using a state-of-the-art THz calorimetry approach correlating spectroscopic to thermodynamic changes, we propose a molecular mechanism of hydrophilic hydration driving GMP self-assembly as a function of temperature. The free energy contribution of hydrophilic hydration is shown as a decisive factor in guanine-quadruplex formation. Our findings spotlight the role of hydration in the formation of macromolecular structures and suggest the potential of hydration tuning for regulating DNA transcription and replication.

Here, we report the frequency-dependent spectrum of ice Ih in the range of 0.2–2 THz. We confirm the presence of a feature that blue-shifts from around 1.55–1.65 THz with a decreasing temperature from 260 to 160 K. There is also a change in the trend of the refractive index of ice corresponding to a dispersion, which is also around 1.6 THz. The features are reproduced in data acquired with three commercial terahertz time-domain spectrometers. Computer-simulated spectra assign the feature to lattice translations perpendicular to the 110 and 1̄10 planes of the ice Ih crystal. The feature’s existence should be recognized in the terahertz measurements of frozen aqueous solution samples to avoid false interpretations.

Terahertz (THz) imaging and optical coherence tomography (OCT) are of great importance in non-destructive testing and medical diagnostics, offering complementary data on similar length scales. This study primarily investigates a method designed to enhance our understanding and measurement of hydrated biological samples by merging OCT and THz data through an iterative algorithm. Initially applied to a flat silicone step wedge with varying thicknesses, the method was validated and extended to gelatin samples with varying water content. By integrating multiple measurements from different sample locations, the algorithm not only confirms the expected refractive indices but also consistently determines thickness measurements. The demonstrated utility of this approach in accurately assessing biologically relevant materials highlights its potential application of interest in corneal diagnostics. Such advancements are particularly vital for improving the accuracy and reliability of measurements crucial for managing corneal diseases.

Corrosion presents significant economic implications across various industries. Its impact is far-reaching, affecting infrastructure, transportation, manufacturing, and energy sectors. To combat this problem, new coatings are being developed that must adhere well to the metal surface, have minimal thickness, and resist delamination over time. The adhesion of the coating is key to achieving its design lifespan, and coatings applied according to the manufacturer’s recommendations typically offer good adhesion to the substrate and can resist corrosive agents. The adhesion of the coating is dependent on various factors, including coating properties, substrate cleanliness, surface roughness, and pre-treatments before application. Here, we present a recent study that explored the impact of surface roughness profile morphology and height on the pull-off adhesion strength value of the coating and its correlation with interfacial adhesion at the coating and substrate. The study revealed that delamination of coatings on steel can be detected using terahertz reflection spectroscopy, which correlates well with standard industry pull-off testing. The findings suggest that THz reflection spectroscopy can be used for non-destructive testing of anticorrosion coatings and the aging process.

Central nervous system (CNS) injuries and neurodegenerative diseases have markedly poor prognoses and can result in permanent dysfunction due to the general inability of CNS neurons to regenerate. Differentiation of transplanted stem cells has emerged as a therapeutic avenue to regenerate tissue architecture in damaged areas. Electrical stimulation is a promising approach for directing the differentiation outcomes and pattern of outgrowth of transplanted stem cells, however traditional inorganic bio-electrodes can induce adverse effects such as inflammation. This study demonstrates the implementation of two organic thin films, a polymer/reduced graphene oxide nanocomposite (P(rGO)) and PEDOT:PSS, that have favorable properties for implementation as conductive materials for electrical stimulation, as well as an inorganic indium tin oxide (ITO) conductive film. Transcriptomic analysis reveals that electrical stimulation improves neuronal differentiation of SH-SY5Y cells on all three films, with the greatest effect for P(rGO). Unique material- and electrical stimuli-mediated effects are observed, associated with differentiation, cell-substrate adhesion, and translation. The work demonstrates that P(rGO) and PEDOT:PSS are highly promising organic materials for the development of biocompatible, conductive scaffolds that will enhance electrically-aided stem cell therapeutics for CNS injuries and neurodegenerative diseases.

Contact lenses are widely used for correcting refractive errors and treating various ocular disorders. However, their thickness and refractive index can change over time due to dehydration and mechanical stress, which can impact their optical performance and safety. In this study, we introduce a new method to measure these parameters using a combined terahertz and optical coherence tomography system. An iterative algorithm that combines information from multiple locations within the sample can provide the depth information and refractive index measurements for both THz and OCT frequencies. We applied this method to contact lenses and measured their thickness and refractive index at different time intervals. The results revealed significant changes in these parameters over time, highlighting the importance of proper monitoring. Overall, this novel method provides accurate and reliable measurements of contact lens thickness and refractive index over time, providing essential insights into their behavior in vivo.

Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a ‘snapshot’ introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation.

The feasibility of a 220 - 330 GHz zero order axicon generated Bessel beam for corneal water content was explored. Simulation and experimental data from the 25-degree cone angle hyperbolic-axicon lens illuminating metallic spherical targets demonstrate a monotonically decreasing, band integrated, backscatter intensity for increasing radius of curvature from 7 - 11 mm, when lens reflector and optical axis are aligned. Further, for radii >= 9.5 mm, maximum signal was obtained with a 1 mm transverse displacement between lens and reflector optical axes arising from spatial correlation between main lobe and out of phase side lobes. Thickness and permittivity parameter estimation experiments were performed on an 8 mm radius of curvature, 1 mm thick fused quartz dome over a 10 mm axial span. Extracted thickness and permittivity varied by less than 25 μm and 0.2 respectively after correction for superluminal velocity. Estimated water permittivity and thickness of water backed gelatin phantoms showed significantly more variation due to a time varying radius of curvature.

The self-assembly of the nucleoside guanosine monophosphate (GMP) into complex DNA secondary structures, in aqueous solution is concentration and temperature dependent. It is a unique phenomenon that provides a basis for studying more complicated structures related to DNA. In the present study, we show that distinct features in the terahertz spectrum (30 to 400 cm -1 , 0.8 – 12 THz) are associated with the formation of GMP dimers and quadruplexes, and that these can be attributed to changes in the hydration water and intra-molecular modes of the aggregated structures. This finding establishes a basis for further investigation into secondary DNA structures using terahertz radiation, such as G-quadruplex and i-motif.

Corrosion is a significant economic problem, accounting for up to 5% of the Global GDP. New coatings are being developed to prevent corrosion, but they must bond well with the metal surface, have a minimal thickness, and not delaminate over time. Coating adhesion is crucial for the coating system to attain its design lifetime. Coatings applied following the manufacturer’s recommendations generally offer good adhesion to the substrate and can resist the permeation of corrosive agents. Coating adhesion depends on the coating property and substrate cleanliness, surface roughness, and any pre-treatments before coating application. The study evaluated the effects of surface roughness profile morphology and height on the pull-off adhesion strength value of the coating and its correlation with interfacial adhesion at the coating and substrate. The results show that delamination of coatings on steel used to protect the material from corrosion can be detected using terahertz reflection spectroscopy. The THz data agree well with standard industry pull-off testing. The study provides evidence that THz reflection spectroscopy can be used for non-destructive testing of anticorrosion coatings and the aging process.

Future remote imaging systems promise spectroscopic functionalities extending well beyond the visible wavelengths. This allows real-time spectral information to be gathered from multiple wavelength bands which is highly attractive for numerous remote sensing spectroscopy/imaging applications and aids target recognition. This paper briefly presents a micro-electromechanical systems (MEMS) based electrically tuneable adaptive filter technology developed for the technologically important infrared (IR) bands of the electromagnetic spectrum and reports on the progress towards extension to the significantly longer wavelength THz band. The demonstrated concepts focus on merging MEMSenabled dynamic modulation with the spectral sensitivity and selectivity of metamaterials, as well as on the possibility of adopting the rapidly evolving 3D printing technologies.

Millimeter wave (MMW) radiation does not have enough energy to ionize atoms or molecules and therefore does not have the potential to cause DNA damage. It is expected that this radiation can deteriorate the viability of cancer cells in the tumor while healthy tissue remains unaffected. However, considering the aggressiveness of cancer cells in terms of their motility and invasiveness, MMW radiation-related thermal alterations in the exposed tumor and its environment may trigger cancer cell detachment and further spread. In this study, we looked into changes in cell adhesion and motility of a triple-negative breast cancer cell exposed to MMW radiation and compared it to an epithelial cell subjected to the same treatment.

The secondary structures of nucleic acids are crucial to the regulation of genomic activities, and could potentially serve as a marker for some cancers. Question remains whether such structures could have distinct absorption features in the terahertz range, including a 1.6 THz peak absorption previously reported in methylated DNA. In this study, we examine the terahertz absorption spectrum of G-quadruplex (G4), a key secondary DNA structure that has been closely linked to cancer. The results show that in its most basic form, made up of self-assembled guanosine monophosphate (GMP), there are no distinct features. This result provides a reference for our ongoing investigation on other secondary structures of nucleic acids, and suggests that abnormal population of G4, as found in some cancers, may not be detectable via terahertz absorption spectroscopy.

The current understanding of the biological effects of millimeter waves (MMWs) remains incomplete, and the interaction mechanisms causing these effects are largely unknown. We found that exposure of primary human fibroblasts to MMWs results in modified DNA secondary structure formation, altering the transcriptome and enriching many biological pathways without inducing DNA damage. This establishes the potential for therapeutic application of MMWs to induce targeted modifications to genomic architecture for the purpose of controlling gene expression and specific pathways.

In the terahertz spectroscopy of bimolecular solutions, freezing reduces the background absorption. For example, the absorption coefficient of room temperature water is 237 $^{-1}$ at 1 THz, whereas that of ice is 6.8 cm $^{-1}$ at 173 K. Lower background absorption highlights any spectral features originating from the biomolecule. A reliable baseline spectrum of ice is thus crucial. Despite the interest in biomedical applications, theoretical models and experimental data related to ice are still lacking in the literature, thus hindering progress in the cryogenic measurement of biological samples. We previously reported a highly consistent absorption spectrum of ice in the 0.2 to 2 THz range, which has a profile with a noticeable change of gradient at 1.6 THz. This work extends our investigation into the origin of this feature. Specifically, we investigate whether it is due to scattering by air bubbles, or whether it is an inherent nature of the molecular structure of ice.