Multi-Stimuli Responsive Magnetic Core-Shell Particles: Synthesis, Characterization and Specific RNA Recognition

Temperature responsive magnetic@ poly(divinylbenzene)@ poly(N-isopropylacrylamide-co-acrylic acid) [magnetic@ P(NIPAm-AA)] polymer submicron particles were prepared by seed emulsion polymerization process. At first, divinylbenzene (DVB) cross-linked magnetic seed particles were obtained by emulsion polymerization of DVB while using potassium persulfate (KPS) as an initiator in the presence of oil-in-water magnetic emulsion. DVB cross-linked magnetic polymer particles were used as seed in the precipitation polymerization of N-isopropylacrylamide (NIPAm) to induce temperature sensitive poly(NIPAm) shell onto the hydrophobic surface of the DVB cross-linked magnetic polymer particles. To insert carboxylic acid functional groups (-COOH) in the temperature responsive poly(NIPAm) backbone, the functional monomer acrylic acid (AA) was used to polymerize with NIPAm while N,N-methylenebisacrylamide (MBA) and ammonium persulfate (APS) were used as a cross-linker and as an initiator respectively. The effect of AA on the magnetic particles behaviour has also been studied. Dynamic Light scattering (DLS) results indicate that magnetic poly(DVB)/poly(NIPAm-AA) composite particles undergo volume phase transition with increasing temperature. The effect of AA content, pH and ionic strength has been studied on the volume phase transition temperature of the functional magnetic particles. The deprotonation of - COOH groups due to the increasing of pH (> pKa) enhances zeta potential as well as particles swelling. The pH dependent size swelling and zeta potential change depend on the amount of acrylic acid (AA) used in the polymerization recipe. The magnetic core and polymer shell structure of the particles prepared was confirmed by Transmission Electron Microscopy (TEM). Further characterizations of the particles were done by the thermogravimetry analysis (TGA), FTIR and Magnetization measurement by ABM. Finally, the carboxylic acid functionalized magnetic/poly(DVB)/poly(NIPAm-AA) particles' surface was modified with 3-amino phenylboronic acid (APBA) using 'grafting to' technique to prepare cis-diol containing RNA recognizable boronic acid functionalized magnetic particles.