Titanium dioxide coating of porous silicon microparticles towards nanomedicine applications

Porous silicon (pSi) is a photoluminescent material with a sponge-like structure. The pSi light emitting microparticles are produced by anodization etching of crystalline Si wafer in HF solution and are stable for years in ethanol after a surface carboxyl-functionalization. They are biodegradable, biocompatible, inert and do not activate the immune response system. Furthermore, they have a porosity with large surface to volume ratio, thus being promising for targeting drug delivery and bioimaging. One of the main issues in the application of this material to nanomedicine is its degradation and photoluminescence (PL) fast quenching in aqueous environment. To preserve these properties, organic coatings are used (i.e. PEG, Chitosan). However, such thick coatings often limit the pore size volume and thus the loading capacity. In this study, we deposited an inorganic (TiO2) thin layer on the pSi microparticles surface by ALD (Atomic Layer Deposition) in a rotary reactor, without modifying the structure, as it was confirmed by TEM images (Figure 1). We obtained PL stabilization for almost one year in aqueous media (i.e. PBS – phosphate buffered saline). To investigate the toxicity of pSi-TiO2 microparticles, we performed in-vitro tests by incubating different amounts of microparticles in human DCs (dendritic cells). They were internalized without any toxic effect by the DCs and maintained the PL, as confirmed by two photon absorption experiment. These promising results of optical stability and “compatibility” with human DCs open the way for future developments of inorganic coating of pSi microparticles to a complete platform for drug delivery achieve and bioimaging applications.