This probe was designed to target the microenvironment around tumours and becomes optically active in the present of cathepsins and matrix remodelling49 with cleavage of the Arg–Lys bond by cathepsins K, L, S and B (Fig. 9) liberating the Cy5 fluorophore (excitation and emission wavelengths are 649 nm and 670 nm). This evidence concerns the gene CTSS and neoplasm.