Proteins play a key role in living organisms. The study of proteins and their dynamics provides information about their functionality, catalysis and potential alterations towards pathological diseases. Several techniques are used for studying protein dynamics, e.g., magnetic resonance, fluorescence imaging techniques, mid-infrared spectroscopy and biochemical assays. Spectroscopic analysis, based on the use of terahertz (THz) radiation with frequencies between 0.1 and 15 THz (3–500 cm−1), was underestimated by the biochemical community. In recent years, however, the potential of THz spectroscopy in the analysis of both simple structures, such as polypeptide molecules, and complex structures, such as protein complexes, has been demonstrated. The THz absorption spectrum provides some information on proteins: for small molecules the THz spectrum is dominated by individual modes related to the presence of hydrogen bonds. For peptides, the spectral information concerns their secondary structure, while for complex proteins such as globular proteins and viral glycoproteins, spectra also provide information on collective modes. In this short review, we discuss the results obtained by THz spectroscopy in the protein dynamics investigations. In particular, we will illustrate advantages and applications of THz spectroscopy, pointing out the complementary information it may provide.

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.

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.

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.

In this work we introduce the first step toward the development of an Infrared (IR) sensoristic platform aiming to the detection and discrimination of airborne pathogens. SARS-CoV-2 Spike glycoprotein (S) is considered as a biomarker for virus recognition. A comparative spectroscopic analysis is illustrated, studying Spike glycoprotein subunit S1 from three different viruses, MERS-CoV, SARS-CoV and SARS-CoV-2. Moreover, SARS-CoV-2 variants are also investigated. The IR characterization of their S1 secondary conformation was carried out through Attenuated Total Reflection (ATR), analyzing the Amide I absorption band. In addition, pH-dependent conformational changes of SARS-CoV-2 S1 were investigated, too

All coronaviruses are characterized by spike glycoproteins whose S1 subunits contain the receptor binding domain (RBD). The RBD anchors the virus to the host cellular membrane to regulate the virus transmissibility and infectious process. Although the protein/receptor interaction mainly depends on the spike’s conformation, particularly on its S1 unit, their secondary structures are poorly known. In this paper, the S1 conformation was investigated for MERS-CoV, SARS-CoV, and SARS-CoV-2 at serological pH by measuring their Amide I infrared absorption bands. The SARS-CoV-2 S1 secondary structure revealed a strong difference compared to those of MERS-CoV and SARS-CoV, with a significant presence of extended β-sheets. Furthermore, the conformation of the SARS-CoV-2 S1 showed a significant change by moving from serological pH to mild acidic and alkaline pH conditions. Both results suggest the capability of infrared spectroscopy to follow the secondary structure adaptation of the SARS-CoV-2 S1 to different environments.