Paramagnetic Quantum Dots as Multimodal Probes for Potential Applications in Nervous System Imaging

An axonal tracer that can be detected by both magnetic resonance imaging (MRI) and fluorescence is of great interest for studying nerve regeneration, particularly for spinal cord injury repairs. In this study, we develop a new type of multifunctional nanoparticle that combines three different functionalities of paramagnetism, fluorescence, and axonal tracing into one nanomaterial. We demonstrate that the new synthesized quantum dot nanoparticles have good biocompatibilities and can be readily taken up by cells. In addition, the quantum dots show excellent longitudinal and transverse relaxivities (i.e. r 1 = 11.22 ± 0.10 mM −1 s −1 and r 2 = 24.50 ± 0.51 mM −1 s −1 ) at 1.5 T, MRI contrast properties better than those of Magnevist®, a commercially available MRI contrast agent. The UV–vis absorbance spectra of all the pQDs-BDA samples indicate that these tracers are stable at different temperatures. Taken together, this new nanomaterial demonstrates good performances for both optical and MR imaging modalities, suggesting its promising potential applications in non-invasive imaging, particularly as a novel multimodal axonal tracer for nervous system imaging.