Infrared spectroscopy characterization of MERS-CoV, SARS-CoV and SARS-CoV-2 spike proteins for sensoristic platform.

Motivated by the request to monitor the airborne pathogens, like viruses, using ultrasensitive vibrational spectroscopy, we propose a comparative infrared spectroscopic study of viral glycoprotein spikes (S) of MERS-CoV, SARS-CoV and SARS-CoV-2, for the first time, at least to our knowledge. The aim is the investigation of a part of the pathogen, in this case the structural S proteins and their complex secondary structure that match the protein functionality, observing the amide I band ({1590\mbox$--$1730 ${cm^{-1}}$) in serological ambient and their potential differences. We experimentally observed that the three viruses have S proteins with different secondary conformations. SARS-CoV-2 has a secondary conformation characterized by the formation of intermolecular $\beta$-sheet structures, linked to the ability to anchoring virus-human receptors. Moreover, we also proved that the conformation of SARS-CoV-2 strongly change by passing from an alkaline to mild acid environment. Instead, the results pave the way to use vibrational spectroscopy as an alternative monitoring approach, overcoming the limitations of conventional bio-chemical ones.