Fig. 1.

Illustration of the tumour-selective cascade activatable self-detained system (TCASS) and its molecular design. a the modularized peptide-based molecules consisted of four sections: (i) recognition motif: AVPIAQK was the binding motif; (ii) DEVD was the enzymatically degradable linker; (iii) KLVFFAECG was the self-assembly motif; and (iv) cyanine dye (Cy) or doxorubicin (DOX) was functional molecule. b the mechanism of the specific recognition, molecular cleavage and in situ self-assembly of molecule 1. First, molecule 1 was specifically recognized by X-linked inhibitor of apoptosis protein (XIAP); then the caspase-3/7, activated by the recognition process, cleaved the molecules; further, the cleaved molecules rapidly self-assembled in situ and formed fibrous β-sheet superstructures; finally, the β-sheet nanostructures significantly enhanced the accumulation and retention of functional molecule in tumour tissue