Nature Communications 6: Article number: 6938 (2015); Published 24 April 2015; Updated 12 June 2015. This Article contains errors in the author affiliation 1 and in Figs 2 and 6. The correct details for affiliation 1 are given below: 1Department of Chemistry and Laboratory of Advanced Materials, iChEm (Collaborative Innovation Center of Chemistry for Energy Materials), State Key Laboratory of Molecular Engineering of Polymers, Fudan University, Shanghai 200433, China. In Fig. 2g, the emission spectrum was inadvertently duplicated from Fig. 2c during the production process. An error was also introduced in the transition represented in Fig. 2l. This panel represents the 4F9/2–4I15/2 transition. Furthermore, a wrong scale bar definition was provided in the figure caption. The scale bars represent 100 nm. In Fig. 6a, the ‘PR’ and ‘ER’ labeling of MCF-7 and MDA-MB-231 cell images were inadvertently switched during manuscript preparation. The blue fluorescence of sb-UCNPs-Anti-ER should have been labelled ‘ER’, and the green fluorescence of sb-UCNPs-Anti-PR should have been labelled ‘PR’. Corrected versions of both figures appear below.