We have previously shown the effective deliveryof DAPRin- andaffibody-modified nanoparticles to cancer cells, such as anti-HER2DARPin-liposomes,22 anti-HER2 DARPin-modifiedmagnetic nanoparticles,23 affibody-decoratedpolymer particles,24 and DARPin-modifiedgold nanorods.25 But now there is no informationon the direct comparison of these two classes of molecules for nanoparticletargeting. Here, ERBB2 is linked to cancer.