1：Experimental Design and Method Selection:

The study involved synthesizing Cu2-xSe nanocrystals and forming heterostructures with gold via spontaneous redox reactions in aqueous solution. Methods included TEM, HRTEM, XRD, XPS, UV-Vis-NIR spectroscopy, and various biological assays to evaluate photothermal conversion, radiosensitization, cytotoxicity, and in vivo imaging and therapy.

2：Sample Selection and Data Sources:

4T1 tumor cells and 3T3 normal cells were used for in vitro studies. BALB/c mice bearing 4T1 tumors were used for in vivo experiments. Data were sourced from laboratory syntheses and animal models.

3：List of Experimental Equipment and Materials:

Equipment included transmission electron microscope (FEI Tecnai G20), high-resolution TEM (JEOL ARM-200F), X-ray diffractometer (Shimadzu XRD-6000), XPS (Thermo Scientific Sigma Probe), UV-Vis-NIR spectrophotometer (PerkinElmer Lambda 750), infrared thermal imaging camera (FLIR A65), confocal microscope (PerkinElmer UltraViewVoX), flow cytometer, CT imaging system (MILabs), SPECT/CT system (MILabs), photoacoustic imaging scanner (MSOT, iThera Medical). Materials included CuSO4·5H2O, BSA, HAuCl4·4H2O, SeO2, Vitamin C, HS-PEG-SH, and other chemicals from specified suppliers.

4：Experimental Procedures and Operational Workflow:

Synthesis of Cu2-xSe nanoparticles and heterostructures with gold, surface modification with PEG, characterization using various techniques, in vitro assays for photothermal conversion, cytotoxicity, colony formation, DNA damage, apoptosis, and in vivo studies for blood circulation, immunological response, multimodal imaging (PA, CT, SPECT), and therapy (PTT and RT combined).

5：Data Analysis Methods:

Data were analyzed using statistical methods, including colony formation assays fitted with exponential models, isobologram analysis for synergy, and various imaging and biological data quantification techniques.