One-pot synthesis and strong near-infrared upconversion luminescence of poly(acrylic acid)-functionalized YF3:Yb3+/Er3+ nanocrystals

Abstract

This paper describes the synthesis of new upconverting luminescent nanoparticles that consist of YF 3 :Yb 3+ /Er 3+ functionalized with poly(acrylic acid) (PAA). Unlike the upconverting nanocrystals previously reported in the literature that emit visible (blue-green-red) upconversion fluorescence, these as-prepared nanoparticles emit strong near-infrared (NIR, 831 nm) upconversion luminescence under 980 nm excitation. Scanning electron microscopy, transmission electron microscopy, and powder X-ray diffraction were used to characterize the size and composition of the luminescent nanocrystals. Their average diameter was about 50 nm. The presence of the PAA coating was confirmed by infrared spectroscopy. The particles are highly dispersible in aqueous solution due to the presence of carboxylate groups in the PAA coating. By carrying out the synthesis in the absence of PAA, YF 3 :Yb 3+ /Er 3+ nanorice materials were obtained. These nanorice particles are larger (~700 nm in length) than the PAA-functionalized nanoparticles and show strong typical visible red (668 nm), rather than NIR (831 nm), upconversion fluorescence. The new PAA-coated luminescent nanoparticles have the pottential be used in a variety of bioanalytical and medical assays involving luminescence detection and fluorescence imaging, especially in vivo fluorescence imaging, due to the deep penetration of NIR radiation.

Highly-sensitive multiplexed in vivo imaging using pegylated upconversion nanoparticles

“…However, the background autofluorescence in traditional fluorescence imaging techniques significantly limits the imaging sensitivity, especially for in vivo imaging in which the tissues and food residues exhibit strong background fluorescence [6]. In the past few years, studies on upconversion nanoparticles (UCNPs), usually containing lanthanide ions (Ln 3+ ), have grown rapidly owing to their wide applications in solidstate lasers, three-dimensional flat-panel displays, low-intensity infrared (IR) imaging, bioprobes, and bioimaging [7][8][9][10][11][12][13][14]. Compared with traditional downconversion fluorescent dyes and QDs, near infrared (NIR)-to-visible upconversion optical bioprobes have a number of advantages.…”

Nanoparticles for multimodal in vivo imaging in nanomedicine

“…As a good example, therefore, Wang et al reported on the upconversion NPs that emit NIRF luminescence -831 nm by using excitation of 980 nm -to minimize the absorption problems. 60 In summary, optical imaging has various advantages, including high sensitivity, low cost, short acquisition time of images, and safety. While it is true that NIR fluorophores improve tissue-penetration depth, the depth is not still sufficient to overcome a big hurdle for human in vivo imaging.…”

Functionalized nanomaterials: their use as contrast agents in bioimaging: mono- and multimodal approaches

“…When judiciously coated, some YF 3 :Yb 3 + /Er 3 + NPs lead to upconversion luminescence in the NIR (831 nm) rather than in the visible, which enables a greater penetration of the light [141] . Other examples include core@shell NdF 3 @ SiO 2 ( α -NaYbF 4 :Tm 3 + )@CaF 2 , NaGdF 4 :Nd 3 + @NaGdF 4 NPs, which also have excitation and emission in the NIR range and efficient deep-tissue imaging of small animals [133,142] .…”