Silica-Based Nanoparticles for Intracellular Drug Delivery - Intracellular Delivery: Fundamentals and Applications - page 346

Fig. 5 Schematic illustration of bioconjugation strategies applied to silica nanoparticles (Reproduced
with permission from Wang et al. 2006 . Copyright 2006 American Chemical Society)

could be altered due to electrostatic interactions with charged functional groups.
For instance, a post-coating with amine-containing organosilane compounds could
be neutralized by the negative surface charge of nanoparticles at neutral pH, so that
the overall charge of the material will drop down, leading to colloidal instability and
then to severe particle aggregation in aqueous medium. To circumvent this draw-
back, inert negatively-charged organosilanes could be introduced, such as phospho-
nates, that will play the role of dispersing agents acting during the post-grafting.
As a consequence, the particles, that will have a net negative charge, will be again
well dispersed in aqueous solution (Santra 2004 ). After surface modification with
different functional groups, nanoparticles can then act as scaffolds for the grafting
of biological moieties such as DNA oligonucleotides, aptamers, antibodies or pep-
tides, etc. As examples, carboxyl-modified nanoparticles, having pendant carboxylic
groups, are good candidates for covalent coupling of proteins or other amine-
containing biomolecules; thiol-functionalized nanoparticles can immobilize disulfide-
modified oligonucleotides via disulfide-coupling chemistry; amine-modified
nanoparticles can be coupled to a wide variety of haptens and drugs via succinimidyl
esters and iso(thio)cyanates (Wang et al. 2006 ) (Fig. 5 ).

3.3 Mesoporous Silica Nanoparticles (MSN)

Different kinds of drugs were evaluated for release by mesoporous silica materials. Vallet-
Regi and co-workers have demonstrated the release of ibuprofen (Vallet-Regi 2006 ),