ERBB2 and breast cancer: To demonstrate the feasibility of the multiplexed labelling, multicolour sb-UCNPs emitting at 480, 540 and 650 nm were directly conjugated with primary antibodies (Abs) against the three most important breast cancer biomarkers (oestrogen receptors (ERs), progesterone receptors (PRs) and human epithelial growth fator receptor-2 (HER2)), which are routinely analysed in surgical pathology laboratories and on which therapeutic decisions are based (Fig. 1).