A ‘designer nanoparticle’ system that can be rapidly engineered in a tunable and unambiguous manner, trz-PLP binds to oncogenically active human epidermal growth factor receptor 2 (HER2) and is internalized by HER2 overexpressing subtypes of breast cancer cells, but not by breast cancers lacking HER2 amplified breast cancers. This evidence concerns the gene ERBB2 and breast carcinoma.