Are upconverting Ln3+ based nanoparticles any good for deep tissue imaging with retention of optical sectioning?

Frank C. J. M. van Veggel; Jothirmayanantham Pichaandi; John-Christopher Boyer; Kerry R. Delaney

doi:10.1117/12.906775

2 February 2012 Are upconverting Ln³⁺ based nanoparticles any good for deep tissue imaging with retention of optical sectioning?

Frank C. J. M. van Veggel, Jothirmayanantham Pichaandi, John-Christopher Boyer, Kerry R. Delaney

Author Affiliations +

Proceedings Volume 8232, Colloidal Nanocrystals for Biomedical Applications VII; 823219 (2012) https://doi.org/10.1117/12.906775
Event: SPIE BiOS, 2012, San Francisco, California, United States

Abstract

An effective strategy is presented to make spherical Ln³⁺ doped NaYF4 nanoparticles that show upconversion, with the aim of deep-tissue optical imaging. Upconversion is the conversion of two or more low-energy photons into one of higher energy, e.g. 980 nm to 545 and 680 nm and 980 nm to 800 nm. In order to avoid the formation of nanoparticles with an aspect ratio, we developed a strategy in which subsequent shells were grown on spherical seed nanoparticles. The last shell is undoped in order to improve the optical properties. In addition, a simple intercalation strategy involving the oleate ligands on the surface has been developed to make the nanoparticles dispersible in aqueous solutions and physiological buffers. Two-photon upconversion laser scanning microscopy (TPULSM) and two-photon upconversion wide-field microscopy (TPUWFM) have been tested for their suitability in deep-tissue imaging with retention of lateral and depth resolution (also called optical sectioning). TPULSM can be used up to ~ 600 μm deep, but takes inordinately long times to acquire, which is due to the fact that the absorption cross section of Yb³⁺ is low, the quantum yield of the upconversion process are << 1%, and the Ln³⁺ excited states are up to several hundreds of μs. Hence UCNPs in general are not very bright (i.e. large emitted photon flux). The TPUWFM seems more promising because acquisition times are only several minutes, with depth profiling up to 400 μm. We show the first optical sectioning with this technique in the brain of a mouse, through a thin shaved skull.

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Frank C. J. M. van Veggel, Jothirmayanantham Pichaandi, John-Christopher Boyer, and Kerry R. Delaney "Are upconverting Ln³⁺ based nanoparticles any good for deep tissue imaging with retention of optical sectioning?", Proc. SPIE 8232, Colloidal Nanocrystals for Biomedical Applications VII, 823219 (2 February 2012); https://doi.org/10.1117/12.906775

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KEYWORDS

Nanoparticles

Upconversion

Tissue optics

Brain

Microscopy

Absorption

Photons

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