To assess the effectiveness of the NPs-X4C4-Ab and NPs-PEG5kDa-Ab as immunoplasmonics protein tags in biological samples, we performed a one-step immunolabelling procedure with two breast cancer cell lines, MDA-MB-231 and SK-BR-3, which exhibit different levels of CD44, Her2 and EpCAM protein expressions. The gene discussed is ERBB2; the disease is breast cancer.