Upconverting nanoparticles

This comparison of the spectroscopic properties of the different types of fluorescent reporters underlines that semiconductor QDs and upconverting nanoparticles have no analogs in the field of organic dyes. Therefore, their unique features are unrivaled. The different molecular labels detailed here each display unique advantages that can compete with some of the favorable features of QDs and upconverting phosphors such as long lifetimes in the case of MLC systems and lanthanide chelates or very narrow emission bands for lanthanide chelates beneficial for spectral multiplexing. 

Achatz, D., Ah, R., Wolfbeis, O., 2011. Luminescent chemical sensing, hiosensing, and screening using upconverting nanoparticles. In Prodi, L., Montalti, M., Zaccheroni, N. (Eds.), Luminescence Applied in Sensor Science. Springer, Berlin, Heidelberg, pp. 29-50. 

Park, Y.I., et al. Upconverting nanoparticles a versatile platform for wide-field two-photon microscopy and multi-modal in vivo imaging. Chemical Society Reviews 44, 1302-1317 (2015)... 

Chatteijee DK, Zhang Y. Upconverting nanoparticles as nanotransducers for photodynamic therapy in cancer cells. Nanomedicine 2008 3(1) 73. 

Wang H-Q, Thomas N (2010) Upconverting nanoparticles. Springer Ser Fluoresc doi ... 

This chapter focuses on the synthesis, characterisation, derivatisation and application of rare-earth-doped, upconverting nanoparticles. Principles and applications of bulk upconverting phosphors have been reviewed recently [7]. The same applies to physical and theoretical details [1]. Different synthesis methods for rare-earth-doped, upconverting nanoparticles will be introduced (Sect. 2), and their effect on the properties of the resulting nanoparticles or nanocrystalline material will be discussed. As nanoparticles need to be derivatised to be used in almost any application, a special emphasis will be given to the derivatisation and phase-transfer of upconverting nanoparticles (Sect. 3). Finally, some potential applications of these nanocrystals will be discussed (Sect. 4). 

T able 1 Upconverting nanoparticles, synthesis methods and ligands... 

Arrested precipitation can be performed in many different ways most simply, two solutions containing ions of a poorly soluble salt are mixed within a template. Alternatively, ions (or reactants) can be released slowly as described in stage 1 of the LaMer mechanism. Subsequently, nucleation and growth take place within the template. Furthermore, arrested precipitation can be combined with other methods of synthesis such as the sol-gel method. In that case, a gel is precipitated within the template and condensed in a second step. AU of these variations have been used to synthesise upconverting nanoparticles. 

Sol-gel methods involve typically three steps first, dissolution of metal salts in a mostly aqueous solvent (formation of the sol), second, formation of a gel, and third, condensation of the gel. The products of sol-gel methods resemble those of combustion syntheses as the final step involves typically sintering at high temperatures. Therefore, the same limitations regarding the application of nanocrystalline upconverting nanoparticles apply for both methods. 

To date, the vast majority of applications using upconverting nanoparticles or nanocrystalline material are to be found in the field of bioanalytics or medical diagnostics. This is not surprising because synthesis methods of upconverting nanocrystals are still in their infancy, and the advantages of using these nanocrystals are most obvious in the life sciences. 

In 2005, Li et al. developed a FRET system with biotinylated NaYF4 Yb/Er upconverting nanoparticles (diameter ca. 50 nm) as energy donor and biotinylated gold nanoparticles as energy acceptors [46]. They applied it to detect trace amounts of avidin, and a detection limit of 0.5 nM was achieved. 

It can be concluded that upconverting nanoparticles show significant advantages when used in the field of life sciences. However, only very preliminary work has been done so far. It can be expected that this technology will advance rapidly as high quality upconverting nanoparticles as described, for example, in Sect. 2.6 will be exploited for bioanalytics and medical diagnostics and therapy. 

Gorris HH, Wolfbeis OS (2013) Photo-upconverting nanoparticles for optical encoding and multiplexing of cells, biomolecules, and microspheres. Angew Chem Int Ed 52 3584-3600... 

Bogdan N, Vetrone F, Roy R et al (2010) Carbohydrate-coated lanthanide-doped upconverting nanoparticles for lectin recognition. J Mater Chtan 20 7543—7550... 

Cheng T, Ortiz RF, Vedantham K, Naccache R, Vetrone F, Marks RS, et al. Tunable chemical release from polyester thin film by photocatalytic zinc oxide and doped LiYp4 upconverting nanoparticles. Biomacromolecules 2014 16(1). 

Luminescent Chemical Sensing, Biosensing, and Screening Using Upconverting Nanoparticles... 

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