PTT of xenograft tumors with targeted Ag-PEG-HER2 nanoparticles and light irradiation. (a): Immunohistochemistry of BT/NanoLuc primary tumor tissue and HercepTest controls: negative control (0), normal HER2 expression (1+), and HER2 overexpression (3+) (scale 100 µm). (b): Dynamics of BT/NanoLuc tumor growth under the treatment with repeated injections of PBS, Ag-PEG-HER2 nanoparticles, and Ag-PEG-HER2 with 1 h post blue light irradiation (n = 3 for each group), ** p < 0.05. (c): Bioluminescent imaging of BT/NanoLuc xenograft tumors before treatment (day 7 after inoculation) and after treatment (day 80) and ex vivo imaging of primary tumors (day 90).