Figure 2.

Three principal targeting strategies for nanoprobes: In the absence of an external excitation source, active targeting probes do not migrate from blood vessels into surrounding tissues. Some passive targeting and activatable probes can enter surrounding tissues via the enhanced permeability and retention effect. However, under these conditions, activatable probes lack drug activity (depicted as gray). When pathological changes, such as cancer, occur in the surrounding tissues, active targeting probes can specifically target and penetrate the diseased area. Meanwhile, activatable probes exhibit drug activity (depicted as yellow) under the influence of an external excitation source. This figure was created with Biorender.com.