A critical comparison of lanthanide based upconversion nanoparticles to fluorescent proteins, semiconductor quantum dots, and carbon dots for use in optical sensing and imaging

Abstract

The right choice of a fluorescent probe is essential for successful luminescence imaging and sensing and especially concerning in vivo and in vitro applications, the development of new classes have gained more and more attention in the last years. One of the most promising class are upconversion nanoparticles (UCNPs)-inorganic nanocrystals capable to convert near-infrared light in high energy radiation. In this review we will compare UCNPs with other fluorescent probes in terms of (a) the optical properties of the probes, such as their brightness, photostability and excitation wavelength; (b) their chemical properties such as the dispersibility, stability under experimental or physiological conditions, availability of chemical modification strategies for labelling; and (c) the potential toxicity and biocompatibility of the probe. Thereby we want to provide a better understanding of the advantages and drawbacks of UCNPs and address future challenges in the design of the nanocrystals.

Assessing the protective effects of different surface coatings on NaYF4:Yb3+, Er3+ upconverting nanoparticles in buffer and DMEM

“…NaYF 4 :20%Yb 3+ ,2%Er 3+ UCNP were synthesized according to a previously reported procedure 26 – 28 with some modifications 25 , 44 . Surface modifications and silica coating experiments followed published procedures 45 – 49 .…”

“…UCNP are commonly synthesized in apolar solvents using hydrophobic oleic acid as a capping agent 2 , 22 , 23 , which makes them dispersible only in apolar solvents. To render them water dispersible for applications in biological systems, they must undergo surface modification either by ligand exchange or addition of a new coating (ligand addition or encapsulation) on top of the initially present surface ligands 24 – 26 . Several ligand exchange procedures have been reported so far 24 , 25 , 27 – 31 , such as the exchange of the oleate ligands for polyacrylic acid (PAA) 6 , polyethylene glycol (PEG) 7 , phosphonate ligands 32 , citrate 8 , or removal of the oleate ligand with NOBF 4 /DMF yielding “naked” UCNP stabilized with electrostatically adsorbed BF 4 ¯ 9 .…”

Long‐Term Colloidal and Chemical Stability in Aqueous Media of NaYF4‐Type Upconversion Nanoparticles Modified by Ligand‐Exchange

“…The absence of any background fluorescence in biological media due to the unique optical properties of the upconversion of low energy photons in the near‐infrared (NIR) region into high energy emissions in the visible or UV makes this material promising for biological applications. But this comes with several challenges like chemical and colloidal stability in aqueous media or the controlled functionalization by a defined number of receptor molecules . Most upconversion nanoparticles described in literature are consisting of a NaYF 4 host lattice as this materials has a preferable low phonon‐energy (≈300 cm −1 ) compared to other host materials like fluorides (LiYbF 4, ≈460 cm −1 ), oxides (Y 2 O 3 , ≈591 cm −1 ), or vanadates (YVO 3 , ≈890 cm −1 ).…”

Carbon Dots as New Generation Materials for Nanothermometer: Review

“…Compared to other fluorescent raw materials, CDs are produced from inexpensive carbon sources that are abundant in nature [91]. Furthermore, there are several simple methods to modify and functionalize the surface state of CDs, which allow tailoring the solubility, stability, physicochemical properties, and quantum yields of CDs according to their experimental requirements [49,92,93].…”