The key role of ergothioneine in surface-enhanced Raman scattering spectra of biofluids

Surface-enhanced Raman scattering (SERS) spectroscopy has lately attracted attention in the field of liquid biopsy as a quick and reasonably inexpensive technology that could dramatically improve clinical diagnosis and prognosis. SERS spectra, in fact, provide information about a collection of metabolites present in the studied biofluid, providing biochemical insight into specific health status. Ergothioneine, an unusual dietary amino acid containing the imidazole-2-thione substructure, is important because it is one of the few metabolites in biofluids that can be detected directly (without recognition elements) by SERS. In the past decade, many studies characterizing biofluids or other biological samples have unknowingly linked this amino acid with crucial metabolic processes, including inflammation, in a variety of disorders. With some exceptions, most studies on serum or plasma reported a higher relative amount of ergothioneine in control samples with respect to those of patients affected by a disease. However, because the SERS spectrum of ergothioneine was only recently reported by this group, most previous investigations mistakenly ascribed what are now recognized as spectral bands of this chemical to other compounds. This presentation will summarize and re-evaluate the knowledge about the role of this compound in the so-called “label-free” SERS spectra of biofluids, in order to better understand the role of this compound in numerous clinical conditions.