|Mohammad Sameti1, Carsten Kneuer1, Udo Bakowsky1, Dagobert Hoebbel2, Zsuzsa Csögör2, Helmut Schmidt2, and Claus-Michael Lehr1
1Saarland University, Biopharmaceutics and Pharmaceutical Technology, Geb. 8.1, Im Stadtwald, D-66123 Saarbrücken, Germany, and
We report on the synthesis and characterization of silica nanoparticles and particle-plasmid complexes (nanoplexes). As previously reported, surface modified cationic silica nanoparticles bind electrostatically, condense and protect plasmid DNA . Their ability to transfect genes in-vitro and their very low toxicity (LD50 > 1 mg in all cases) has been already demonstrated .
Nanoparticles were synthesized by modification of commercially available silica particles with aminoalkylsilanes. Particle size was determined by laser back scattering. The surface charge was determined by zeta potential titration. The solid state 29Si MAS NMR was used to determine the modification degree of nanoparticles. Silica nanoparticles and nanoparticle-DNA complexes were visualized by atomic force microscopy (AFM). All nanoparticles had a positive surface charge ranging from +7 to +31 mV at pH 7.4 and a mean diameter between 10 and 100 nm. The particle size distribution showed a relatively narrow distribution (±30%). The comparison of 29Si MAS NMR spectra of unmodified silica nanoparticles (IPAST) with aminosilane modified nanoparticles showed a higher condensation degree of SiO2 groups and points to co-condensation of modificator and basis particle. The AFM investigations showed the adsorption of nanoparticles on the DNA strand and fomation of complexes. The mean diameter of these "nanoplexes" was between 140 and 350 nm.