Herein, we report on the rational design and translational development of a first-in-kind ultrasmall nanoparticle drug-immune conjugate, anti-HER2 scFv-SG4015-PEG-Cy5-C′ dots, for dual-modality imaging and therapy of HER2+ expressing gastric cancer utilizing a “hit and run” delivery approach. Here, ERBB2 is linked to gastric cancer.