Upconverting nanoparticles (UCNPs) for deep tissue imaging

One of the ways to improve imaging of the diagnosed tissue is its labeling with luminescent materials (luminophores) or light-scattering nanoparticles and application of optical clearing agents. Examples of luminophores are fluorescent dyes such as fluorescein, which is widely used for visualization of e.g. a blood flow. Spectrally selective registration reduces the background autofluorescence of tissue and improves the localization of the labeled tissue. However, strong absorption and scattering of the probing light as well as fluorescence in the visible spectral range and incomplete suppression of the autofluorescence by spectral methods make this approach a non-ideal solution.

A promising solution of labeling could be the use of anti-Stokes (upconversion) luminophores. A serious hurdle for the use of these materials for deep tissue optical imaging has long been their micron size, making the targeted delivery of these markers in vivo very difficult. However, technological breakthrough of recent years resulted in creation of nano-sized water-soluble anti-Stokes luminophores (upconversion nanoparticles), makes the above-mentioned approach exceptionally attractive. In them, lanthanide-ions e.g. of ytterbium and erbium (or thulium) are embedded into into a NaYF4 matrix and are the main “players” responsible for the optical properties.

A promising solution of labeling could be the use of anti-Stokes (upconversion) luminophores. A serious hurdle for the use of these materials for deep tissue optical imaging has long been their micron size, making the targeted delivery of these markers in vivo very difficult. However, technological breakthrough of recent years [8] resulted in creation of nano-sized water-soluble anti-Stokes luminophores (upconversion nanoparticles), makes the above-mentioned approach exceptionally attractive. In them, lanthanide-ions e.g. of ytterbium and erbium (or thulium) are embedded into a NaYF4 matrix and are the main “players” responsible for the optical properties.

Scanning across a tissue-mimicking slab phantom with an embedded cylindrical vessel containing upconverting nanoluminophores.

Surface distribution of emitted fluorescence from a cylinder (1 mm in diameter) filled with UCNPs located 5 mm under the tissue surface (Monte Carlo simulations); numbers are in watts. Conversion efficiency: 0.01. Imaging area: 50x50 sq. mm; sample depth: 15 mm.

References

A.P. Popov, A.V. Bykov, V. Sokolov, Y.V. Lyska, A. Nadort, A.V. Priezzhev, R. Myllylä, A. Zvyagin, "Upconverting luminophores as a novel tool for deep tissue imaging", Proc. SPIE 8090, 8090V (2011). [PDF]

Last updated: 9.9.2016