Fig. 4. Kinetic analysis of AIE-based substrates toward caspases 3 and 6. (A) Chemical structure of AIE-based substrates for caspases 3 and 6. (B) The efficiency of substrate hydrolysis by caspases 3 and 6. Tetrapeptide AIE substrates with classical sequences (DEVD for caspase 3 and VEID for caspase 6) are efficiently hydrolyzed as their target enzymes. The pentapeptide caspase 6 substrate Ac-EVEID-K-TPE displays very high selectivity over caspase 3. (C) The AIE-based substrate for caspase 6 with homophenylalanine at the P5 position is not suitable for kinetic studies, as it undergoes self-assembly due to high hydrophobicity and yields a strong fluorescent signal in the absence of the enzyme.