ERBB2 and breast cancer: Prior to conjugating scFv fragments to DFO-DBCO-PEG-Cy5-C’ dots, HER2-specific targeting capabilities were demonstrated by incubating the dye-conjugated scFv fragments (i.e., scFv-488, Supplementary Fig. 16) with two well-established breast cancer cell lines exhibiting different HER2 expression signatures, as previously reported34 and confirmed by our western blots (Supplementary Fig. 18): BT-474 (HER2+, 3.7 × 106 receptors per cell) and MDA-MB-231 (HER2−, 7.0 × 104 receptors per cell).