In the last decades, the interest in nanoparticles in the biomedical field experienced a rapid growth because of the tunability of their physical and chemical properties and their rich surface chemistry that enables specific functionalization by design. Different classes of functional nanoparticles, including metals, semiconductors, metal/lanthanide oxides and organic or hybrid systems have found successful application in several medical branches, such as nano-therapy, diagnostics and imaging. Today, one of the most advanced biomedical uses of nanoparticles is offered by their strong interaction with ionizing radiation, which makes it possible to improve the effectiveness of conventional cancer treatments, imaging techniques and radiation dosimetry [1]. In oncological therapies, one of the most adopted medical treatment is radiotherapy (ca. 50% of total cases), a non-invasive technique typically consisting in the local release of the energy of X-rays to stop tumor cells proliferation, either by directly damaging their DNA, or indirectly by forming cytotoxic free radicals [2]. Among the different material classes with potential application in this field, metal halide nanocrystals (NCs) have recently attracted substantial attention for ionizing radiation detection, prized for their high average atomic number (Z) that enhances the interaction probability with ionizing radiation and strong robustness to prolonged exposure to ionizing radiation [3][4][5]. However, despite such promise, very few examples of medical diagnostic and therapeutic strategies based on metal halide NCs have been proposed mainly due to their low stability in aqueous environment resulting in their rapid dissolution and further consequent release of potentially harmful Pb²⁺ ions.

In this talk, we show that multicomponent systems consisting of lead halide perovskite NCs (CsPbX₃-NCs, X=Br, I) grown inside mesoporous silica nanospheres (NSs) with selectively sealed pores are potentially promising candidates for enhanced radiotherapy and radio-imaging strategies, yhanks to the intense scintillation and strong interaction with ionizing radiation of CsPbX₃ NCs with the chemical robustness in aqueous environment of silica particles. We demonstrate that CsPbX₃ NCs boost the generation of singlet oxygen species (¹O₂) in water under X-ray irradiation and the encapsulation into sealed SiO₂ NSs warrants perfect preservation of the inner NCs after prolonged storage in harsh conditions. We find that the ¹O₂ production is triggered by the electromagnetic shower released by the CsPbX₃ NCs with a striking correlation with the halide composition (I₃>I_3-xBr_x>Br₃), without quenching their radioluminescence. This opens to the possibility of designing multifunctional radio-sensitizers able to reduce the local delivered dose and the undesired collateral effects in the surrounding healthy tissues by improving a localized cytotoxic effect of therapeutic treatments and concomitantly enabling optical diagnostics by radio imaging.