Rationale design of a layer-by-layer nanostructure for X-ray induced photodynamic therapy

X-ray induced Photodynamic Therapy (XPDT) is a proposed therapy for deep tumours. The idea is to use the X-ray beam of a standard radiotherapy facility to excite a scintillator which is coupled with a photosensitizing agent which in turn generates reactive oxygen species (ROS) which induce local oxidative stress. Alike in standard Photodynamic Therapy, this oxidative stress may be used to treat tumours. Preliminary results [F. Rossi et al. Sci. Rep. 5 (2015) 7606] demonstrated that can XPDT enhance the efficacy of standard radiotherapy, while reducing its unwanted side effects. This work reports the rationale development of a nanostructure incorporating nanoparticles (NP) for XPDT around a silica core by means of electrostatic adsorption. To this aim, scintillator CeF3 and photosensitizer ZnO, both in form of nanoparticles, have been adsorbed into a polyelectrolyte Layer-by-Layer (LbL) multilayer grown around a SiO2 core. This structure, in a future work, could be a platform for drug delivery. We optimized the growth of the structure basing on results from adsorption on planar substrates, as a function of incubation time, of particle concentration, and of the composition of the outer polyelectrolyte layer, having also in mind the need to avoid the formation of micrometric aggregates. This drove the rationale synthesis of the nanocapsules. The resulting structures are studied by Scanning Electron Microscopy, X-ray Microanalysis, Dynamic Light Scattering, and ζ-potential analysis.