Preclinical X-Ray Fluorescence Imaging with Multifunctional Nanoparticles

Abstract: X-ray fluorescence imaging (XFI) is an emerging technique for preclinical studies, characterized by high resolution, specificity, and sensitivity. It relies on nanoparticles (NPs) as contrast agents, which must be constituted of specific elements that match the X-ray source energy for detection. Laboratory liquid metal-jet X-ray sources enable compact in vivo XFI, thereby extending the accessibility of this imaging technique beyond synchrotron facilities.When designing NPs as contrast agents, biocompatibility is essential for both preclinical and clinical imaging, often requiring a passivating biocompatible coating on the NP surface. The NP cores can provide contrast by their elemental composition, while coating, conjugation, and decoration strategies can add other functionalities and improve biocompatibility.In this thesis, multifunctional NPs are designed to extend the functionality of XFI contrast agents by incorporating optically fluorescent or magnetically active components: conjugated carbon quantum dots, dye-doped silica shell, and decorated superparamagnetic iron oxide NPs. The designed multifunctional NPs allow correlative and multiscale imaging with complementary techniques such as confocal optical microscopy or magnetic resonance imaging (MRI). Furthermore, these NPs also facilitate more comprehensive studies on NP pharmacokinetics, paving the way for more robust investigations in the field of nanomedicine.The benefits of multifunctional NPs are demonstrated with two approaches. First, in vivo correlative imaging with MRI and XFI is shown to reduce false positives caused by MRI artifacts in the lungs and abdomen. Second, XFI is employed to enable rapid NP bioengineering, by iteratively improving NP properties and administration strategies for passive tumor targeting. Optical and X-ray fluorescent multifunctional NPs enable the co-localization of NPs at both macroscopic and microscopic levels with XFI and confocal microscopy, correlating NP accumulation in organs with NP-cell interactions. These results highlight the role of XFI in the field of nanomedicine, with potential applications in pharmacokinetics, tumor targeting, treatment monitoring, and the development of medical devices.