Optical and X-ray Fluorescent Nanoparticles for Dual Mode Bioimaging

Abstract

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 <i>in vitro</i> 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 <i>in vitro</i> to be tracked and studied. <i>In situ</i> XFCT successfully showed the possibility of <i>in vivo</i> 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.