Figure 1.

Chemical design and properties of NE680. (a) The fluorogenic peptide substrate is conjugated to a pharmacokinetic modifier (PKM) and flanked by two NIR fluorophores. Upon cleavage of the peptide by NE, the fluorophores become fluorescent. (b) Absorbance spectra of the NE-activated fluorescent form (dashed line) shows a bathochromic shift in the absorbance maximum relative to the native autoquenched state (solid line). (c) The fluorescence emission is increased more than 30-fold upon proteolytic activation with a maximum at 690 nm (excitation at 665 nm).