Elaboration of a new in vivo imaging system based on multimodal upconversion nanoparticles

Background In vivo imaging can be achieved with various techniques (MRI, CT-scan, PET-scan, scintigraphy, fluorescence…) depending on the nature of the target tissue, cell or tracer. Nevertheless, there is actually no... [ view full abstract ]

Background
In vivo imaging can be achieved with various techniques (MRI, CT-scan, PET-scan, scintigraphy, fluorescence…) depending on the nature of the target tissue, cell or tracer. Nevertheless, there is actually no reference method that allows for optimal results: each technique has advantages and limitations in depth, resolution, sensitivity, tissue damage or cost.

Methods
We have developed multimodal nanoparticles for biological imaging: a Gadolinium oxysulfide core allows MRI and CT-scan imaging whereas the addition of other lanthanides as dopants enables the acquisition of fluorescence properties. The combination of the different techniques gives maximal information with only one tracer. This brings much more flexibility and robustness in the results comparatively to other tracers currently available on the market. We have found that Ytterbium/Thulium codoped nanophosphors are particularly suited for in vivo imaging as they emit strong luminescence after upconversion of near infrared photons. Briefly, this enables the imaging of deeper targets whilst minimizing tissue lesions compared to classical fluorescence obtained after visible laser excitation. Indeed, it benefits from tissue transparency and lower excitation energy.

Findings
Here we report the development of a complete in vivo fluorescence tracking system: Ytterbium/Thulium codoped Gadolinium oxysulfide as tracer and dedicated macroscopic imaging device. Our latest results are very promising: we are able to follow the kidney-injected tracer on the surface of the skin after two months.
This let us foresee real applications to achieve our final goal: over-time detection of nanoparticle-labeled mesenchymal/stromal cells after grafting in a solid organ. In the end, it will signify the availability of an innovative and robust tool for cell therapy proof of concept.