Fluorescence signatures of SARS-CoV-2 spike S1 proteins and an human ACE-2: excitation-emission maps and fluorescence lifetimes

Significance Fast and reliable detection of infectious SARS-CoV-2 virus loads is an important issue. Fluorescence spectroscopy is a sensitive tool to do so in clean environments. This presumes a comprehensive knowledge of fluorescence data. Aim This work aims at providing fully featured information on wavelength and time-dependent data of the fluorescence of the SARS-CoV-2 spike protein S1 subunit, its receptor binding domain (RBD) and the human angiotensinconverting enzyme 2 (hACE2), especially with respect to possible optical detection schemes. Approach Spectrally resolved excitation-emission maps of the involved proteins and measurements of fluorescence lifetimes were recorded for excitations from 220 to 295 nm. The fluorescence decay times were extracted by using a bi-exponential kinetic approach. The binding process in the SARS-CoV-2 RBD was likewise examined for spectroscopic changes. Results Distinct spectral features for each protein are pointed out in relevant spectra extracted from the excitation emission maps. We also identify minor spectroscopic changes under the binding process. The decay times in the bi-exponential model are found to be (2.0 ± 0.1) ns and (8.0 ± 1.0) ns. Conclusions Specific material data serve as important background information for the design of optical detection and testing methods for SARS-CoV-2 loaded media. ### Competing Interest Statement The authors have declared no competing interest.