Towards SERS-based multiplexed monitoring of protease activity using non-natural aromatic amino acids

Abstract

Surface Enhanced Raman Spectroscopy (SERS) allows sensitive and selective detection of protease activity by monitoring the cleavage of specific peptide substrates. Furthermore, it offers the possibility for multiplexing, during which the activity of two (or more) proteases with different specificities is detected simultaneously. To distinguish between the contributions of different proteases, different aromatic amino acids with non-overlapping SERS peaks need to be used as Raman reporters. As the three natural aromatic amino acids only offer limited possibilities for multiplexing, we examined several non-natural aromatic amino acids with the aim of expanding multiplexing possibilities. We recorded their SERS spectra for the Raman shifts of 300-1700 cm–1 and identified their characteristic SERS peaks. Of the examined nonnatural aromatic amino acids, 3-nitro-tyrosine and two phenylalanines containing stable heavy isotopes seem particularly promising for multiplexing applications. Besides exhibiting characteristic SERS peaks in the spectral region of interest, these non-natural aromatics provide strong SERS peaks compared to natural aromatic amino acids, consequently improving detection sensitivity.