Functionalization of Mesoporous Silicon Nanoparticles for Targeting and Bioimaging Purposes

Carboxylic acid functionalized thermally hydrocarbonized porous silicon nanoparticles (UnTHCPSi-NP) were synthesized, and their opsonization and targeting properties were studied in vitro alongside with in vivo biodistribution. The carboxyl groups on UnTHCPSi were utilized to further functionalize the nanoparticles. In order to reduce the opsonization of the UnTHCPSi-NPs, different sized polyethylene glycol (PEG) were conjugated or adsorbed to the NPs surface. The latter approach, based on hydrophobic interaction, turned out to be more effective in reducing the opsonization and improving the stability of the nanoparticle suspension. The most abundant opsonins after plasma incubation were fibrinogen precursors and IgG. Furthermore, the targeting properties of UnTHCPSi-NPs were studied in vitro with antibodies against glutathione S-transferase (anti-GST). PEGylated NPs conjugated with anti-GST bound to GST-agarose in human plasma nearly 35-fold compared to control NPs, indicating that UnTHCPSi-NPs are suitable for targeting in physiological environment. The in vivo biodistribution in mice revealed that PEGylated UnTHCPSi-NPs, accumulate fast into the liver and the spleen, regardless of the reduced opsonization in vitro. However, autoradiography and transmission electron microscopy showed that majority of the NPs still remained in hepatic blood vessels and sinusoids suggesting a possibility to utilize them as a sustained release platform for payload molecules.