Objective:To prepare nanoprobes by using polydopamine (PDA) as a carrier which is modified with the sonosensitizer protoporphyrin Ⅸ (PpⅨ) and labeled with 131I, 99Tc m or 177Lu, and to explore the value of these new nanoprobes in diagnosis and combination therapy of breast cancer. Methods:PDA particles were synthesized by aqueous oxidation, and a layer of polyethylene glycol (PEG) and PpⅨ were modified on the surface to product PDA-PEG-PpⅨ. Then the nuclides 131I, 99Tc m and 177Lu were labeled on PDA, respectively, and the labeling yield and stability were determined. The cytotoxicity test was conducted by comparing the viabilities of 4T1 tumor cells in free 131I group and 131I-PDA-PEG-PpⅨ group. The 4T1 cells were divided into 7 groups according to different treatment methods: PDA-PEG-PpⅨ group, PDA-PEG-PpⅨ+ photothermal therapy (PTT) group, PDA-PEG-PpⅨ+ sonodynamic therapy (SDT) group, 131I-PDA-PEG-PpⅨ+ PTT group, 131I-PDA-PEG-PpⅨ+ SDT group, 131I-PDA-PEG-PpⅨ+ PTT+ SDT group (100 μg/ml PDA-PEG-PpⅨ, 925 kBq/ml 131I), and the control group (DMEM culture medium). The cell viabilities of those groups were compared to evaluate the therapeutic effect. 4T1 tumor bearing mouse models were established, then 99Tc m-PDA-PEG-PpⅨ was injected through the tail vein (29.6 MBq) or intratumorally (14.8 MBq) to perform gamma imaging. The independent-sample t test and one-way analysis of variance were used for data analysis. Results:The PDA particles were uniform in size, with a particle size of (160.0±1.5) nm. They had a good photothermal conversion effect. A characteristic peak consistent with PpⅨ (400 nm) appeared in the UV-Vis absorption spectrum of PDA-PEG-PpIX. In the cytotoxicity test, when the radioactivity was 1.850 or 3.700 or 7.400 MBq/ml, the cell viabilities of free 131I group and 131I-PDA-PEG-PpⅨ group were significantly different ((72.18±6.57)% vs (86.07±5.17)%, (59.31±9.06)% vs (80.85±4.21)%, (42.90±1.30)% vs (72.99±5.73)%; t values: 3.71, 4.82, 11.46, P values: 0.006, 0.001, <0.001). The 131I-PDA-PEG-PpⅨ+ PTT+ SDT combination therapy had a better killing effect on 4T1 tumor cells than the combination of 131I-PDA-PEG-PpⅨ+ PTT and 131I-PDA-PEG-PpⅨ+ SDT (cell viabilities: (10.09±2.50)% vs (16.04±2.63)%, (28.65±4.72)%; F=351.66, P<0.001). In vivo imaging showed that 99Tc m-PDA-PEG-PpⅨ was stable in mouse models and could be effectively enriched in tumors. Conclusions:A multifunctional nanoprobe based on PDA is successfully prepared. The radionuclide labeling method is simple and effective, with a good stability. 131I-PDA-PEG-PpⅨ can kill 4T1 cells efficiently. 99Tc m-PDA-PEG-PpⅨ has an obvious tumor concentration effect in mouse models.