Optical and X-ray Fluorescent Nanoparticles for Dual Mode Bioimaging

Nanoparticle (NP) based contrast agents detectable via different imaging modalities (multimodal properties) provide a promising strategy for noninvasive diagnostics. Core-shell NPs combining optical and X-ray fluorescence properties as bioimaging contrast agents are presented. NPs developed earlier for X-ray fluorescence computed tomography (XFCT), based on ceramic molybdenum oxide (MoO₂) and metallic rhodium (Rh) and ruthenium (Ru), are coated with a silica (SiO₂) shell, using ethanolamine as the catalyst. The SiO₂ coating method introduced here is demonstrated to be applicable to both metallic and ceramic NPs. Furthermore, a fluorophore (Cy5.5 dye) was conjugated to the SiO₂ layer, without altering the morphological and size characteristics of the hybrid NPs, rendering them with optical fluorescence properties. The improved biocompatibility of the SiO₂ coated NPs without and with Cy5.5 is demonstrated in vitro by Real-Time Cell Analysis (RTCA) on a macrophage cell line (RAW 264.7). The multimodal characteristics of the core-shell NPs are confirmed with confocal microscopy, allowing the intracellular localization of these NPs in vitro to be tracked and studied. In situ XFCT successfully showed the possibility of in vivo multiplexed bioimaging for multitargeting studies with minimum radiation dose. Combined optical and X-ray fluorescence properties empower these NPs as effective macroscopic and microscopic imaging tools.