To demonstrate the selective accumulation of UCNP-DARPin-LoPE-s on the HER2-expressing cell surface, we employed fluorescence microscopy tuned to excite and acquire UCNP photoluminescence signal, where SKOVip-kat cells transfected to express far-red fluorescence proteins were used as the HER2-positive tumor cell model. This evidence concerns the gene ERBB2 and neoplasm.