Cytotoxicity was evaluated by incubating human OE33 (EGFR+/ErbB2+) cancer and Qh-TERT (EGFR-/ErbB2-) benign esophageal cells and SKBr3 (EGFR+/ErbB2+) human breast cancer cells with HB-Au-NPs for 24 h, Figure S4. Here, ERBB2 is linked to cancer.