The authors wish to note, "The colony formation assay for SNU-1 upon enoxacin treatment in Fig. 1B is incorrect because of inadvertent duplication with the SNU-638 sample during the preparation of the figure. We have now replaced it with the correct assay. The data for RKO.shTRBP in Fig. 3C were erroneously graphed because the mean fold change was derived from an incorrect Fig. S5A where the formula used for quantitative RT-PCR analysis was ΔctAssay/ΔctControl rather than the correct formula 2-(ΔctAssay-ΔctControl). The data for RKO.shTRBP in Fig. S5A and CRC56 and CRC43 in Fig. S9B were erroneously graphed because of the same error with the formula. The corrected figures and their legends appear below. The figures in the supplemental information have also been corrected. These errors do not affect the conclusions of the article. We sincerely regret these mistakes. The error bars on the graphs used throughout the article indicate standard deviation (SD)."The corrected Fig. 1, Fig. 3, Fig. S5, and Fig. S9 appear below, along with their corresponding legends. The SI has been corrected online.

Several strategies for linking antibodies (Abs) through their Fc region in an oriented manner have been proposed at the present time. By using these strategies, the Fab region of the Ab is available for antigen molecular recognition, leading to a more efficient interaction. Most of these strategies are complex processes optimized mainly for the functionalization of surfaces or microbeads. These methodologies imply though the Ab modification through several steps of purification or the use of expensive immobilized proteins. Besides, the functionalization of magnetic nanoparticles (MNPs) turned out to be much more complex than expected due to the lack of stability of most MNPs at high ionic strength and non-neutral pH values. Therefore, there is still missing an efficient, easy and universal methodology for the immobilization of nonmodified Abs onto MNPs without involving their Fab regions during the immobilization process. Herein, we propose the functionalization of MNPs via a two-steps strategy that takes advantage of the ionic reversible interactions between the Ab and the MNP. These interactions make possible the orientation of the Ab on the MNP surface before being attached in an irreversible way via covalent bonds. Three Abs (Immunoglobulin G class) with very different isoelectric points (against peroxidase, carcinoembryonic antigen, and human chorionic gonadotropin hormone) were used to prove the general applicability of the strategy here proposed and its utility for the development of more bioactive NPs.