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All coronaviruses are characterized by spike glycoproteins whose S1 subunit contains the receptor binding domain anchoring the virus to the host cellular membrane and regulating virus transmissibility and infectious process. Although the protein/receptor interaction depends on the spike secondary-conformation, in particular to its S1 unit, few is known about the secondary-structure of different coronaviruses. In this paper the S1 conformation is investigated for MERS-CoV, SARS-CoV and SARS-CoV-2 in serological condition, by measuring their Amide I infrared vibrational absorption bands. The SARS-CoV-2 secondary structure reveals a strong difference in comparison to MERS-CoV and SARS-CoV ones, with a higher amount of intermolecular β-sheet content. Moreover, the conformation of SARS-CoV-2 S1 shows a significant change by moving from serological pH and mild acidic to alkaline pH conditions close to the bat ecological niche. Both results suggest a huge capability of SARS-CoV-2 S1 glycoprotein to adapt its secondary structure to different environments.

Two-color plasma, induced by two lasers of different colors, can radiate ultra-broadband and intense terahertz (THz) pulses, which is desirable in many technological and scientific applications. It was found that the polarization of the emitted THz depends on the phase difference between the fundamental laser wave and its second harmonic. Recent investigation suggests that chirp-induced change of pulse overlap plays an important role in the THz yield from two-color plasma. However, the effect of laser chirp on THz polarization remains unexplored. Hereby, we investigate the impact of laser chirp on THz polarization. It is unveiled that the chirp-induced phase difference affects THz polarization. Besides, positive and negative chirps have opposite effects on the variation of the THz polarization versus the phase difference. The polarization of THz generated by a positively chirped pump laser rotates clockwise with an increasing phase difference, while it rotates anticlockwise when generated by a negatively chirped pump laser.

Superconducting split ring resonator arrays allow to overcome two main limitations affecting metallic metamaterial resonating in the Terahertz (THz) range: Ohmic losses and tunability of their optical response. In this work, we design and experimentally realize direct and complementary square arrays of superconducting YBa2Cu3O7 (YBCO) split ring resonators working in the THz spectral range. The main purpose of this paper is to show how the metamaterial resonances can be tuned by temperature (T) when crossing the superconducting transition temperature Tc of YBCO. The tuning property can be quantified by describing the THz transmittance of the patterned YBCO films vs. T through a model of coupled resonators. This model allows us to estimate the THz resonances of split-ring arrays and their interaction, showing how the kinetic inductance Lk in the superconducting state is the main parameter affecting the metamaterial properties.

In the last decades, Mars has been widely studied with on-site missions and observations, showing a planet that could have hosted life in the past. For this reason, the recent and future space missions on the red planet will search for traces of past and, possibly, present life. As a basis for these missions, Space Agencies, such as the European Space Agency, have conducted many experiments on living organisms, studying their behavior in extraterrestrial conditions, learning to recognize their biosignatures with techniques remotely controllable such as Raman spectroscopy. Among these organisms, the radioresistant cyanobacterium Chroococcidiopsis was irradiated during the STARLIFE campaign with strong radiative insults. In this article we have investigated this cyanobacterium using Raman spectroscopy and extended the characterization of its biosignatures and its response to the radiative stress to the mid- Infrared and Terahertz spectral region using the Fourier Transform InfraRed (FT-IR) and Terahertz Time Domain spectroscopy (THz- TDs), which demonstrates the compatibility and suitability of these techniques for future space missions.

Volatile organic compounds are released by different sources causing air pollution. Moreover, some of these carbon-based organic chemicals are considered as biomarkers in the exhaled breath of individuals and can be used to identify various kinds of diseases. Hence, the increasing demand to control air quality and human health has promoted the development of monitoring systems based on high-performance gas sensing structures. This review highlights the achievements in sensing technologies for the detection of volatile organic compounds. Particularly, chemiresistive gas sensors and detection systems based on the terahertz spectroscopy method are outlined. The progress in research studies is discussed and the potential of both techniques is evaluated considering the current challenges. Afterward, a brief summary is also provided along with the advances and issues for future investigations and the manufacturing of highly sensitive and selective monitoring systems.

Human exposure to Volatile Organic Compounds (VOCs) and their presence in indoor and working environments is recognized as a serious health risk, causing impairments of varying severities. Different detecting systems able to monitor VOCs are available in the market; however, they have significant limitations for both sensitivity and chemical discrimination capability. During the last years we studied systematically the use of Fourier Transform Infrared (FTIR) spectroscopy as an alternative, powerful tool for quantifying VOCs in air. We calibrated the method for a set of compounds (styrene, acetone, ethanol and isopropanol) by using both laboratory and portable infrared spectrometers. The aim was to develop a new, and highly sensitive sensor system for VOCs monitoring. In this paper, we improved the setup performance, testing the feasibility of using a multipass cell with the aim of extending the sensitivity of our system down to the part per million (ppm) level. Considering that multipass cells are now also available for portable instruments, this study opens the road for the design of new high-resolution devices for environmental monitoring.

Due to a significant influence of strontium (Sr) on bone regeneration, Sr substituted beta-tricalcium phosphate (Sr-TCP) cement is prepared and investigated by short- and long-term time-resolved techniques. For short-term investigations, energy-dispersive X-ray diffraction, infrared spectroscopy, and, for the first time, terahertz time-domain spectroscopy techniques are applied. For long-term time-resolved studies, angular dispersive X-ray diffraction, scanning electron microscopy, mechanical tests, and behavior in Ringer solution are carried out. After 45 min of the cement setting, the Sr-TCP phase is no longer detectable. During this time period, an appearance and constant increase of the final brushite phase are registered. The compressive strength of the Sr-TCP cement increases from 4.5 MPa after 2 h of setting and reaches maximum at 13.3 MPa after 21 d. After cement soaking for 21 d in Ringer solution, apatite final product, with an admixture of brushite and TCP phases is detected. The cytotoxicity aspects of the prepared cement are investigated using NCTC 3T3 fibroblast cell line, and the cytocompatibility-by human dental pulp mesenchymal stem cells. The obtained results allow to conclude that the developed Sr-TCP cement is promising for biomedical applications for bone tissue.

The recent pandemic of SARS-CoV-2 virus has made evident critical issues relating to virus sensing and the need for deployable tools for adequate, rapid, effective viral recognition on a large-scale. Although many conventional molecular and immuno-based techniques are widely used for these purposes, they still have some drawbacks concerning sensitivity, safety, laboriousness, long-term collection and data analysis. Therefore, new rapidly emerging approaches have been introduced such as terahertz (THz)-based technologies. In this contribution, we summarize the emerging THz radiation technology, its solutions and applications for high-sensitivity viral detection.

Motivated by the increasing demand to monitor the air-quality, our study proved the feasibility of a new compact and portable experimental approach based on Terahertz (THz) continuous wave high resolution spectroscopy, to detect the presence of the air's contaminants as greenhouse gases (GHG) and volatile organic compounds (VOCs). In this specific work, we first characterized, determining their molar absorption coefficient in the spectral region (0.06-1.2) THz, the pure optical response of the vapor of five VOCs: methanol, ethanol, isopropanol, 1-butanol and 2-butanol. In particular, 1-butanol and 2-butanol are characterized for the first time in literature at THz frequencies. Then we studied the optical response of their mixtures achieved with ambient air and ethanol. The results show that it is possible for a differentiation of single components by describing their spectral absorption in terms of the linear combination of pure compounds absorption. This proof of concept for this apparatus study and set-up paves the way to the use of THz Continuous wave high resolution spectroscopy for the environmental tracking of air pollutants. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

The growing demand for innovative means in biomedical, therapeutic and diagnostic sciences has led to the development of nanomedicine. In this context, naturally occurring tubular nanostructures composed of rolled sheets of alumino-silicates, known as halloysite nanotubes, have found wide application. Halloysite nanotubes indeed have surface properties that favor the selective loading of biomolecules. Here, we present the first, to our knowledge, structural study of DNA-decorated halloysite nanotubes, carried out with nanometric spatially-resolved infrared spectroscopy. Single nanotube absorption measurements indicate a partial covering of halloysite by DNA molecules, which show significant structural modifications taking place upon loading. The present study highlights the constraints for the use of nanostructured clays as DNA carriers and demonstrates the power of super-resolved infrared spectroscopy as an effective and versatile tool for the evaluation of immobilization processes in the context of drug delivery and gene transfer.

Virus sensing is earning great interest for recognition of dangerous and widely spread diseases, such as influenza A (virus subtypes H1N1, H3N2 etc), severe acute respiratory syndrome, Middle East respiratory syndrome etc. Many molecular and biological techniques have been developed and adopted for virus detection purposes. These techniques show some drawbacks concerning long collection time and data analysis, sensitivity, safety, costs etc. Therefore, new sensing approaches have been proposed for overcoming these limitations. In this short-review, we explore the emerging and challenging terahertz radiation technology and its applications to virus high-sensitivity remote-sensing devices.

We present here a small-scale liquid Helium (LHe) immersion cryostat with an innovative optical setup suitable to work in long wavelength radiation ranges and under applied magnetic field. The cryostat is a multi stage device with several shielding in addition to several optical stages. The system has been designed with an external liquid Nitrogen boiler to reduce the liquid bubbling. The optical and mechanical properties of the optical elements were calculated and optimized for the designed configuration while the optical layout has been simulated and optimized among different configurations based on the geometry of the device. The final design has been optimized for low noise radiation measurements of proximity junction arrays under applied magnetic field in the wavelength range $\lambda$=250-2500 $\mu$m.

HMQ-TMS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 2,4,6-trimethylbenzenesulfonate) is a recently discovered anisotropic organic crystal that can be exploited for the production of broadband high-intensity terahertz (THz) radiation through the optical rectification (OR) technique. HMQ-TMS plays a central role in THz technology due to its broad transparency range, large electro-optic coefficient and coherence length, and excellent crystal properties. However, its anisotropic optical properties have not been deeply researched yet. Here, from polarized reflectance and transmittance measurements along the x 1 and x 3 axes of a HMQ-TMS single-crystal, we extract both the refraction index n and the extinction coefficient k between 50 and 35,000 cm &minus, 1 . We further measure the THz radiation generated by optical rectification at different infrared (IR) wavelengths and along the two x 1 and x 3 axes. These data highlight the remarkable anisotropic linear and nonlinear optical behavior of HMQ-TMS crystals, expanding the knowledge of its properties and applications from the THz to the UV region.

Sensing devices have become a necessary part of our daily lives with a wide range of applications including in healthcare and environmental safety. Metal oxide nanomaterials are very promising candidates for the fabrication of next-generation sensing systems due to their attractive physical, chemical and electronic properties. However, the improvement of their performances to satisfy the modern requirements in sensing technologies remains a challenging issue. Inspired by natural processes, we report a novel green synthesis approach for the preparation of WO3 nanomaterials. We developed a hydrothermal synthesis method and performed the thermal treatment of tungsten thin films using sodium chloride and distilled water. Meanwhile, we studied the effect of water, sodium chloride and water vapor on the formation of nanomaterials. The morphological, compositional and structural investigations of samples demonstrate that it is possible to prepare porous materials composed of polycrystalline WO3 nanoparticles in an aqueous solution of sodium chloride and upon exposure to water vapor. Both materials show a good selective response to acetone compared to different interfering gases. The limits of detection of the samples prepared in sodium chloride-containing water and upon exposure to water vapor are 170 and 220 ppb, respectively. We propose that the effect of environmental humidity is more evident on the functional stability of WO3 nanostructures fabricated upon exposure to water vapor due to the presence of relatively big porous regions on their surface. However the crystal structure of WO3 nanoparticles has a significant effect on their sensing response and selectivity. The monoclinic γ-WO3 structure is more reactive and selective to acetone compared to orthorhombic β-WO3. We attribute this feature to the catalytic activity and large dipole moment of monoclinic γ-WO3. Thus, this work provides a new strategy based on green chemistry for the preparation of WO3 nanomaterials and their application in health and environmental monitoring.

We demonstrate graphene on flexible, low-loss, cyclo-olefin polymer films as transparent electrodes for terahertz electro-optic devices and applications. Graphene was grown by chemical vapor deposition and transferred to cyclo-olefin polymer substrates by the thermal release tape method as layers on an approximate area of 4 cm2. The structural and electromagnetic properties of the graphene samples as well as their spatial variation were systematically mapped by means of µRaman, terahertz time-domain and mid-infrared spectroscopy. Thanks to the small thickness and very low intrinsic absorption of the employed substrates, both high transmittance and conductivity were recorded, demonstrating the suitability of the technique for the fabrication of a new class of transparent and flexible electrodes working in the terahertz spectrum.

Exposure to styrene is a major safety concern in the fibreglass processing industry. This compound is classified by the International Agency for Research on Cancer as a possible human carcinogen. Several types of analytical equipment exist for detecting volatile organic compounds (VOCs) in the atmosphere; however, most of them operate ex-situ or do not provide easy discrimination between different molecules. This work introduces an improved and portable method based on FTIR spectroscopy to analyse toxic gaseous substances in working sites down to a concentration of less than 4 ppm. Styrene and a combination of VOCs typically associated with it in industrial processes, such as acetone, ethanol, xylene and isopropanol, have been used to calibrate and test the methodology. The results demonstrate that the technique offers the possibility to discriminate between different gaseous compounds in the atmosphere with a high degree of confidence and obtain very accurate quantitative information on their concentration, down to the ppm level, even when different VOCs are present in a mixture.

THz-based technologies and research applications have seen a rapid increment in recent period together with the development of novel radiation sources based both on relativistic electrons and laser techniques. In this framework, laser-induced plasma filament plays an important role in generating intense and broadband THz radiation. Although many attentions have been paid to THz emission from two-color plasma filaments, one-color plasma emission has been scarcely investigated. In particular, the polarization state of one-color THz emission is still controversial due to the limitations of the existing THz detection techniques, which are incapable of simultaneously detecting elliptically and radially polarized THz radiation. In this manuscript, we develop a novel detection method and unambiguously demonstrate for the first time that one-color laser-induced plasma filament simultaneously emits elliptically and radially polarized THz radiation. These polarization states suggest that the generation mechanism results from electric quadrupole, showing a new route for producing more complex polarization states and THz vortex beams.

In this work the terahertz spectra of benzene, toluene, p-xylene and styrene–four volatile organic compounds (VOCs) of interest in environmental pollution studies–have been measured in their liquid phase at room temperature using terahertz time-domain spectroscopy (THz-TDS). Their frequency-dependent refractive index and absorption coefficient have been extracted and analyzed in the spectral range from 0.2 to 2.5 THz. The optical properties of bi-component VOCs mixtures have also been investigated and described in terms of a linear combination of pure VOCs optical components.

Understanding the viscosity of mantle-derived magmas is needed to model their migration mechanisms and ascent rate from the source rock to the surface. High pressure&ndash, temperature experimental data are now available on the viscosity of synthetic melts, pure carbonatitic to carbonate&ndash, silicate compositions, anhydrous basalts, dacites and rhyolites. However, the viscosity of volatile-bearing melilititic melts, among the most plausible carriers of deep carbon, has not been investigated. In this study, we experimentally determined the viscosity of synthetic liquids with ~31 and ~39 wt% SiO2, 1.3 and 1.5 wt% CO2 and 5.7 and 1 wt% H2O, respectively, at pressures from 1 to 4.7 GPa and temperatures between 1265 and 1700 &deg, C, using the falling-sphere technique combined with in situ X-ray radiography. Our results show viscosities between 0.1044 and 2.1221 Pa&middot, s, with a clear dependence on temperature and SiO2 content. The atomic structure of both melt compositions was also determined at high pressure and temperature, using in situ multi-angle energy-dispersive X-ray diffraction supported by ex situ microFTIR and microRaman spectroscopic measurements. Our results yield evidence that the T&ndash, T and T&ndash, O (T = Si,Al) interatomic distances of ultrabasic melts are higher than those for basaltic melts known from similar recent studies. Based on our experimental data, melilititic melts are expected to migrate at a rate ~from 2 to 57 km&middot, yr&minus, 1 in the present-day or the Archaean mantle, respectively.

Recent technological developments in ultrafast laser physics have permitted to make new kind of nonlinear microscopies, as microscopy based on Stimulated Raman scattering. These techniques are based on vibrational contrast mechanism for imaging with high sensitivity, high spatial and spectral resolution and 3D sectioning capability. The interest in the study of lipids and the possibility to image lipid droplets, thanks to their isolated Raman peaks associated with vibrational C-H bond, have encouraged investigation and identification of lipid structures inside cells, taking advantage of Stimulated Raman Scattering (SRS) imaging. In this work, we report and discuss label free images on biological environmental and structural analysis, to detect lipid microstructures inside adipocyte cells.

Stimulated Raman scattering microscopy allows vibrational contrast mechanism for imaging with high spectral and spatial resolution along with three-dimensional sectioning. In this paper, the implementation of a Stimulated Raman Scattering microscope (SRSM), obtained by the integration of a femtosecond SRS spectroscopy set-up with an optical microscope equipped with a scanning unit, is described. Femtosecond Stimulated Raman Scattering microscope is equipped with three femtosecond laser sources: a Ti:Sapphire (Ti:Sa), a synchronized optical parametric oscillator (SOPO) and a frequency converters for ultrafast lasers, i.e. a second harmonic generator optimized for the SOPO. The proposed implementation allows to cover all the regions of Raman spectra, taking advantage of two different laser combinations. The first, Ti:Sa and SHG laser combination can cover in SRL modality the fingerprint region (500 − 1700 cm−1 ) and the silent region. The second, Ti:Sa and OPO, can cover the C-H region or O−H region (2800 − 3200 cm−1 ) in SRG modality. In order to demonstrate its successful realization Stimulated Raman Gain (SRG) and Stimulated Raman Losses (SRL) images of polystyrene beads are reported and discussed.

A subject of wide interest in the physical and life sciences is the noninvasive characterization of microscopic objects within a complex heterogeneous system. In this paper, multiplex stimulated Raman scattering (SRS) is used to investigate complicated biological samples for which calibration of individual components is not easily available. The separation of protein and lipid contribute and the mapping of their simultaneous distributions in single cell achieved by SRS imaging is demonstrated.

In this work, we present successfully realization of a nonlinear microscope, not purchasable in commerce, based on stimulated Raman scattering. It is obtained by the integration of a femtosecond SRS spectroscopic setup with an inverted research microscope equipped with a scanning unit. Taking account of strength of vibrational contrast of SRS, it provides label-free imaging of single cell analysis. Validation tests on images of polystyrene beads are reported to demonstrate the feasibility of the approach. In order to test the microscope on biological structures, we report and discuss the label-free images of lipid droplets inside fixed adipocyte cells.

In the present work, a methodology for the analysis of subcellular morphology with chemical specificity for images from Stimulated Raman Scattering is suggested. In particular, a segmentation method based on a threshold algorithm and on a region growing process, to detect microstructures inside the cells, is proposed. Moreover, quantitative features for the segmented objects are extracted, in order to provide information about the possible morphological variations of microstructures in images acquired by means SRS technique.

In this paper, the implementation and main realization issues of a stimulated Raman scattering (SRS) microscope, obtained by the integration of a femtosecond SRS spectroscopy set-up with an optical microscope equipped with a scanning unit, are described. In order to characterize capabilities and limitations of SRS microscope, the optical resolution is measured and validation tests on polystyrene beads imaging are reported. In addition, taking account of strength of SRS vibrational contrast, label-free imaging of small biological structures, as such as lipid droplets (LDs), in adipocyte cells is carried out. The visualization of small LDs, with dimensions comparable to the optical lateral resolution of our system, is demonstrated.

The visualization of heterogeneous morphology, segmentation and quantification of image features is a crucial point for nonlinear optics microscopy applications, spanning from imaging of living cells or tissues to biomedical diagnostic. In this paper, a methodology combining stimulated Raman scattering microscopy and image analysis technique is presented. The basic idea is to join the potential of vibrational contrast of stimulated Raman scattering and the strength of imaging analysis technique in order to delineate subcellular morphology with chemical specificity. Validation tests on label free imaging of polystyrene-beads and of adipocyte cells are reported and discussed.

Taking advantage of Stimulated Raman scattering, a labelfree single cell imaging technique based on vibrational contrast can be implemented. In this work, the successful realization of a nonlinear microscope, not purchasable in commerce, based on Stimulated Raman scattering is described. In order to test the microscope, polystyrene beads images are carried out. Finally, in order to demonstrate the feasibility of Stimulated Raman scattering imaging, preliminary label free images of adipocyte cell are reported.

This work addresses some key challenges in the fields of bio and nanophotonics by stimulated Raman microscopy. We present the design and the implementation of a femtosecond stimulated Raman scattering microscope, equipped with three femtosecond laser sources, which allows the coexistence of stimulated Raman gain (SRG) and stimulate Raman losses (SRL) detection modes in a single microscopy setup and to generate images of the same region in succession, without adding or removing components. In order to demonstrate the switching between the two detection modes, SRL and SRG images of polystyrene beads are acquired and the images quality are evaluated and compared.

Nonlinear optics at nanoscale is an intriguing research field of great significance from both fundamental and applicative point of view. In this paper, the phenomena of stimulated Raman scattering in both nanostructured silica based materials and nanostructured silicon based materials are investigated and discussed.