Organic dye‐incorporated smart silica‐coated core–shell magnetic nanoparticles (MNP@SiO2) having dual‐functionality (‐PEG/NH2, see Figure) were easily fabricated, and the amine moieties on the NP surface were modified with maleimide functionality for specific covalent immobilization of biopolymers and bioactive small molecules. The sequence‐independent immobilization of antibodies (Ab) is highlighted; Ab‐modified MNP@SiO2 particles exhibit specific recognition for floating tumor cells or target the membrane of adherent breast cancer cells.

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