CTSB and cancer: In the study, researchers created a particular type of amine-rich CDs and then covalently assembled the nucleolin targeting recognition nucleic acid aptamer AS1411 and a CTSB-cleavable peptide substrate that was tethered with chlorin e6 (Ce6), enabling a ratio metric nanoprobe of AS1411-Ce6-CDs that was both cancer-targeting and CTSB stimulus-responsive [61].