Commercially available and synthesized silica particles were fluorescently labeled with FITC and modified to get a wide variety of particle systems with defined size and surface charge. By a variation of reaction conditions particles with diameters of 10 and 80 nm determined with TEM and with zetapotentials between -50 to +30 mV under physiological conditions (pH: 7.4, PBS-buffer) were available.
A further molecular shell consisiting of avidin was obtained by binding the molecules to negatively charged particle surfaces through electrostatic interactions. The amount of avidin coupled to the silica particles was 1.7 μg per mg particle. Starting with particles with an hydrodynamic diameter determined with PCS of 260 nm, the size increased to 500 nm, while the zeta potential was altered to -8 mV under physiological conditions.
Biotinylated wheat germ agglutinin (bio-WGA) can be bonded to such particles through avidin / biotin complex formation. Up to 2.8 μg lectin per mg particles could be coupled to the particle surface. This leads to a further increase of hydrodynamic diameter to 650 nm. It could be shown by hemagglutination test, that the bonded lectin is still active. No toxic effects of the silica particles were found at 1 wt.-% particle concentration with various cell types (Caco-2, L132). The binding of lectin-particle complexes to cells was increased by a factor of 4.4 in comparison to uncoated particles.
In addition it was found that WGA can directly be coupled to the particle surface. An amount of 1.8 μg Lectin per mg particle was determined. The hydrodynamic diameter increases from 260 nm to 432 rm, while a zetapotential of-28 mV was found under physiological conditions.
It could be shown, that negatively charged silica nanoparticles are suitable systems to couple various biomolecules retaining their biological function.