Label-free in-situ monitoring of protein tyrosine nitration in blood by surface-enhanced Raman spectroscopy

A novel label-free method for the in-situ monitoring of protein tyrosine nitration (PTN) was explored based on surface-enhanced Raman spectroscopy (SERS). Benefiting from the relative weak binding ability of sulfate to silver surface, the Raman signals of nitrated peptides were boosted well with sulfate-aggregated silver nanoparticles (Ag NPs). The distinction of the SERS spectra between non-nitrated peptides and nitrated peptides was obtained by directly comparing SERS bands at 330-400cm^-1, allowing the rapid identification of PTN. Furthermore, without any pretreatments, the established method was successfully applied in the rapid in-situ dynamic monitoring of the mimic hemin-catalyzed PTN process in synthetic peptide, bovine serum albumin (BSA), and original human blood serum samples. The results indicated that the proposed approach could be a promising in-situ label-free tool for observing PTN process, which may be quite helpful to deeply understand the mechanism of post-translation modification.