Light emitting functionalized porous silicon microparticles as multimodal system in theranostics

Porous silicon (pSi) is a sponge-like material obtained by anodic porosification of a crystalline silicon wafer in HF; pSi microparticles can be obtained by sonication of the porous layer. This material is characterized by exclusive intrinsic properties that make it suitable for theranostics (i.e. the combination of therapy and diagnostic) with a faster and more specific response to the disease for each patient (i.e. per-sonalized medicine). Due to a quantum confinement effect, this material was found to be photoluminescent at room temperature, allowing its traceability by op-tical imaging in-vitro and in-vivo. The electrochemical etching produces a material with a high surface to volume ratio, making pSi very attractive as a carrier, in per-spective of drug loading and release. Furthermore, the ability to functionalize the surface is essential for the conjugation with other agents (molecules, dyes, magnet-ic nanoparticles, among all) and for further applications (contrast agent in magnet-ic resonance imaging and for photothermal and photodynamic therapy). Optical properties and porosity, together with the biodegradability, the biocompat-ibility and the absence of immunogenicity are the major characteristics to exploit porous silicon microparticles as a multifunctional system in theranostics. Some of its limitations are related to (i) the broad size distribution, due to the top-down fabrication approach, and (ii) its degradation in aqueous media that causes a pho-toluminescence quenching. One of the aims of this PhD thesis work was to overcome these limiting issues in an original and effective approach: (i) an ultrasonic post-functionalization treat-ment and (ii) an inorganic coating based on TiO2 deposition have been experimen-tally validated, respectively. Once fabrication and functionalization protocols are well addressed (first objec-tive of this experimental work), pSi has several potentialities to be improved, for example, combining further diagnostic or therapeutic functionality. Along this di-rection, the second objective of this thesis work, the more applicative one, was the study about adding magnetic properties to this material by infiltrating and attach-ing magnetic nanoparticles inside its pores. As a fundamental step for the reliabil-ity in theranostics, the interaction with human immune cells is explored to evaluate the internalization mechanism, the biocompatibility and the immunogenicity of this system. To complete the trajectory towards theranostics, preliminary results about the employment of pSi microparticles as immune adjuvant delivery are pre-sented, in the perspective of immunotherapy. It is possible, that the presentation of these molecules carried by the microparticles could lead to enhanced cell activa-tion, with respect to the presentation of the soluble molecule.