Composite functional nanomaterials for multimodal imaging and photo-dynamic therapy of sick tissues

Hydrothermal synthesis represents a simple route for the preparation of geomimetic nanomaterials. Within this class, we are focusing on chrysotile nanotubes, as they demonstrate high capability to be surface functionalized [1] together with high biocompatibility and preservation under in vivo conditions [2]. Stoichiometric chrysotile [Mg3Si2O5(OH)4] nanotubes are constituted by a rolled-up double layer of silica, SiO2, and brucite, Mg(OH)2, creating a tubular structure with inner diameter of ca. 7 nm, external diameter of ca. 50 nm, and tunable length ranging from 50 to 1000 nm. Due to the intrinsic strain originating from the crystallographic mismatch between the two layers, the outer one, i.e. that exposed to the external environment, is the brucitic layer. This confers to the nanoparticles dispersed in water solution at pH 7 a z-potential of the order of +30 mV, ensuring stability of colloidal solutions and a useful propensity to form adducts by coulombic interactions with a range of negatively charged functional species [3]. Among them, we selected pH-sensitive fluorescent molecules and ferromagnetic nanoparticles, with the aim to fabricate composite nanomaterials to be employed as i) solid state chemical-optical sensors of pH [4]; ii) multimodal probes for the imaging and targeting of sick tissues [2]; iii) active agents in the X-ray inducible photo dynamic therapy (X-PDT). The acquired magnetic properties permit their use as contrast agent for magnetic resonance imaging, and enable the tracking of tumor cell migration and infiltration responsible for metastatic growth and disease recurrence. Their organic component, changing its fluorescence attitude as a function of local pH, targets the cancer distinctive acidity, and allows localizing and monitoring the tumor occurrence and progression by mapping the acidic spatial distribution within biopsy tissues. The anchored organic component can also act as photosensitizer for the production of singlet oxygen, the reactive species used for the tumor treatment in X-PDT, provided the inorganic nanotube, serving as scintillator, emits light well within the absorption band of the sensitizer. [1] G. De Luca et al., J. Am. Chem. Soc.2009, 131, 6920. [2] C. Villa et al., Adv. Funct. Mater. 2018, 28, 1707582 [3] M. Campione et al., Composite Functional Nanomaterials Assembled via Electrostatic Interactions of Inorganic Surfaces and Organic Molecules, Ed.: Klaus Wandelt, in: Encyclopedia of Interfacial Chemistry, Elsevier, 2018, p. 32-37. [4] A. Monguzzi et. al., Phys. Chem. Chem. Phys. 2014, 16, 2491.