To explore AuNP radiosensitization of XRT of HER2-positive BC, we conjugated AuNPs (30 nm) to trastuzumab through a 5 kDa cross-linker: orthopyridyldisulphide polyethylene glycol-N-hydroxysuccinimide valerate (OPSS-PEG5K-SVA). The gene discussed is ERBB2; the disease is breast cancer.