Synthesis of Monodisperse Biotinylatedp (NIPAAm)-Coated Iron Oxide Magnetic Nanoparticles and Their Bioconjugation to Streptavidin

We describe here the synthesis of 10 nm, monodisperse, iron oxide nanoparticles that we have coated with temperature-sensitive, biotinylated p(NIPAAm) (b-PNIPAAm). The PNIPAAm was prepared by the reversible addition fragmentation chain transfer polymerization (RAFT), and one end was biotinylated with a PEO maleimide-activated biotin to form a stable thioether linkage. The original synthesized iron oxide particles were stabilized with oleic acid. They were dispersed in dioxane, and the oleic acid molecules were then reversibly exchanged with a mixture of PNIPAAm and b -PNIPAAm at 60°C. The b -PNIPAAm-coated magnetic nanoparticles were found to have an average diameter of ~15 nm by dynamic light scattering and transmission electron microscopy. The ability of the biotin terminal groups on the b -PNIPAAm-coated nanoparticles to interact with streptavidin was confirmed by fluorescence and surface plasmon resonance. It was found that the b -PNIPAAm-coated iron oxide nanoparticles can still bind with high affinity to streptavidin in solution or when the streptavidin is immobilized on a surface. We have also demonstrated that the binding of the biotin ligands on the surface of the temperature-responsive magnetic nanoparticles to streptavidin can be turned on and off as a function of temperature.