Core/Shell NaGdF₄:Nd³⁺/NaGdF₄ Nanocrystals with Efficient Near-Infrared to Near-Infrared Downconversion Photoluminescence for Bioimaging Applications

Abstract

We have synthesized core/shell NaGdF4:Nd3+/NaGdF4 nanocrystals with an average size of 15 nm and exceptionally high photoluminescence (PL) quantum yield. When excited at 740 nm, the nanocrystals manifest spectrally distinguished, near infrared to near infrared (NIR-to-NIR) downconversion PL peaked at ~900, ~1050, and ~1300 nm. The absolute quantum yield of NIR-to-NIR PL reached 40% for core-shell nanoparticles dispersed in hexane. Time-resolved PL measurements revealed that this high quantum yield was achieved through suppression of nonradiative recombination originating from surface states and cross relaxations between dopants. NaGdF4:Nd3+/NaGdF4 nanocrystals, synthesized in organic media, were further converted to be water-dispersible by eliminating the capping ligand of oleic acid. NIR-to-NIR PL bioimaging was demonstrated both in vitro and in vivo through visualization of the NIR-to-NIR PL at ~900 nm under incoherent lamp light excitation. The fact that both excitation and the PL of these nanocrystals are in the biological window of optical transparency, combined with their high quantum efficiency, spectral sharpness and photostability, makes these nanocrystals extremely promising as optical biomaging probes.

Neodymium‐Based Stoichiometric Ultrasmall Nanoparticles for Multifunctional Deep‐Tissue Photothermal Therapy

“…[9] In most of the cases, light-induced heating in RENPs is accompanied by the simultaneous generation of a fluorescence signal especially suitable for in vivo imaging. [10] This would be particularly interesting when analyzing the outcome of a photothermal therapy, as fluorescence imaging could be used to monitor the post-treatment evolution of the tumor. Furthermore, RENP fluorescence would also provide the possibility of tracking them in real time after thermal treatment, thus allowing to determine their biodistribution and clearance from the body.…”

Neodymium-doped nanoparticles for infrared fluorescence bioimaging: The role of the host

“…The first demonstration of the capacity of Nd:NPs for in vivo imaging was demonstrated by Prasad and coworkers in 2012. 33 In this pioneering work, authors performed a subcutaneous injection of NaGdF 4 :Nd 3þ NPs into a living mouse (Figure 1(a)). A fluorescence image of this subcutaneous injection was obtained under 808 nm optical excitation by recording the 900 nm signal (corresponding to the 4 F 3/2 !…”

Designed Er^3+-singly doped NaYF_4 with double excitation bands for simultaneous deep macroscopic and microscopic upconverting bioimaging

“…Oleate-capped NaYF 4 :30%Er 3+ @NaYF 4 :2%Er 3+ core-shell nanocrystals in hexane (or chloroform) were transferred into the aqueous phase through a modified ligand-free protocol [27,28]. This ligand-free protocol might achieve stronger overall upconversion luminescence and higher R/G ratio than the oleate-capped ones.…”

“…The signals of red and green emission via 3PE were strong and the images showed a relatively high contrast. The cells maintained in long-strip shape, a symbol of healthy cells, indicating that the ligand-free UCNPs were easily endocytosed by cells and hardly have cytotoxicity [28].…”