Nanoparticles for Cerenkov and Radioluminescent Light Enhancement for Imaging and Radiotherapy

Abstract

Cerenkov luminescence imaging and Cerenkov photodynamic therapy have been developed in recent years to exploit the Cerenkov radiation (CR) generated by radioisotopes, frequently used in Nuclear Medicine, to diagnose and fight cancer lesions. For in vivo detection, the endpoint energy of the radioisotope and, thus, the total number of the emitted Cerenkov photons, represents a very important variable and explains why, for example, ⁶⁸Ga is better than ¹⁸F. However, it was also found that the scintillation process is an important mechanism for light production. Nanotechnology represents the most important field, providing nanosctructures which are able to shift the UV-blue emission into a more suitable wavelength, with reduced absorption, which is useful especially for in vivo imaging and therapy applications. Nanoparticles can be made, loaded or linked to fluorescent dyes to modify the optical properties of CR radiation. They also represent a useful platform for therapeutic agents, such as photosensitizer drugs for the production of reactive oxygen species (ROS). Generally, NPs can be spaced by CR sources; however, for in vivo imaging applications, NPs bound to or incorporating radioisotopes are the most interesting nanocomplexes thanks to their high degree of mutual colocalization and the reduced problem of false uptake detection. Moreover, the distance between the NPs and CR source is crucial for energy conversion. Here, we review the principal NPs proposed in the literature, discussing their properties and the main results obtained by the proponent experimental groups.

Keywords: cerenkov luminescence imaging; cerenkov radiation; gold nanoparticles; nanoclusters; nanocompounds; nanoparticles; photodynamic therapy; rare-earth nanoparticles; silica nanoparticles.

Figure 1

Schematic representation of the Cerenkov light emission process. A beta particle, emitted by a radionuclide, travels in a medium faster than the light speed in the medium itself. The fast de-polarization of the molecules produces a cone of light known as Cerenkov radiation.

Figure 2

Peghilated Quantum dots (a), Au nanoparticles (b) Silica Nanoparticles (c), micelles (d).

Figure 3

Light produced from NPs and the interaction with radionuclides are due to gamma rays which produce gamma scintillation (top), interactions with photons (Cerenkov radiation) which are converted by CRET (middle), and direct interactions with beta particles which produce beta scintillation (bottom).

Figure 4

Schematic representation of ROS production due to CR interaction in TiO₂ NPs, leading to cancer cell apoptosis.