Morphological evolution of upconversion nanoparticles and their biomedical signal generation (original) (raw)
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ACS Applied Nano Materials, 2021
Upconversion nanoparticles are a promising class of materials for bioimaging. Their attractive optical properties are influenced by their crystalline phase, size, and morphology resulting from the preparation method employed. Herein, we synthesized NaYF 4 :Yb,Er nanocrystals by the coprecipitation method followed by a heat treatment step. The influence of the treatment temperature and the type of reactor on the phase transition from the α-cubic to the β-hexagonal phase was investigated. We found that before the phase transition, the size and shape of α-NaYF 4 :Yb,Er nanocrystals evolved due to a coalescence mechanism with microtubular reactors. In contrast to the flask system, we also observed an anisotropic growth of β-NaYF 4 :Yb,Er nanorods in microtubes whose length can be controlled by adjusting the temperature. The diameter of microtubes plays a critical role in the shape evolution of the final products from spheres to nanorods. The type of reactor and thus the resulting temperature gradient could be considered as a promising parameter to control the phase, shape and size of UCNPs without changing the chemical composition.
Scientific Reports
Lanthanide-based, spectrally shifting, and multi-color luminescent upconverting nanoparticles (UCNPs) have received much attention in the last decades because of their applicability as reporter for bioimaging, super-resolution microscopy, and sensing as well as barcoding and anti-counterfeiting tags. A prerequisite for the broad application of UCNPs in areas such as sensing and encoding are simple, robust, and easily upscalable synthesis protocols that yield large quantities of UCNPs with sizes of 20 nm or more with precisely controlled and tunable physicochemical properties from low-cost reagents with a high reproducibility. In this context, we studied the reproducibility, robustness, and upscalability of the synthesis of β-NaYF4:Yb, Er UCNPs via thermal decomposition. Reaction parameters included solvent, precursor chemical compositions, ratio, and concentration. The resulting UCNPs were then examined regarding their application-relevant physicochemical properties such as size, si...
Scientific Reports, 2021
Water-dispersible up-converting nanoparticles (UCNPs) are known to be very effective in biomedical applications. Research groups have paid special attention to the synthesis of hydrophilic UCNPs with good physicochemical properties. Being aware of this, we decided to improve the ligand-free modification method of OA-capped NaYF4:Yb3+,Er3+/NaYF4 UCNPs prepared by precipitation in high-boiling-point solvents as the thus-far reported methods do not provide satisfactory results. Different molarities of hydrochloric acid and various mixing times were selected to remove the organic ligand from the NPs’ surface and to discover the most promising modification approach. Highly water-stable colloids were obtained with a very high reaction yield of up to 96%. Moreover, the acid treatment did not affect the morphology and the size of the product. All of the crystals exhibited a bright up-conversion emission under 975-nm excitation, which confirmed the two-photon excitation and effective energy ...
Nanoscale, 2015
We present a systematic study on the effect of surface ligands on the luminescence properties and colloidal stability of β-NaYF 4 :Yb 3+ ,Er 3+ upconversion nanoparticles (UCNPs), comparing nine different surface coatings to render these UCNPs water-dispersible and bioconjugatable. A prerequisite for this study was a large-scale synthetic method that yields ∼2 g per batch of monodisperse oleate-capped UCNPs providing identical core particles. These ∼23 nm sized UCNPs display an upconversion quantum yield of ∼0.35% when dispersed in cyclohexane and excited with a power density of 150 W cm −2 , underlining their high quality. A comparison of the colloidal stability and luminescence properties of these UCNPs, subsequently surface modified with ligand exchange or encapsulation protocols, revealed that the ratio of the green (545 nm) and red (658 nm) emission bands determined at a constant excitation power density clearly depends on the surface chemistry. Modifications relying on the deposition of additional (amphiphilic) layer coatings, where the initial oleate coating is retained, show reduced nonradiative quenching by water as compared to UCNPs that are rendered water-dispersible via ligand exchange. Moreover, we could demonstrate that the brightness of the upconversion luminescence of the UCNPs is strongly affected by the type of surface modification, i.e., ligand exchange or encapsulation, yet hardly by the chemical nature of the ligand.
The Journal of Physical Chemistry C, 2017
In the field of biomedicine, upconversion nanoparticles have wide ranging applications from bioimaging to targeted cargo delivery, especially due to their excellent chemical and optical properties in comparison to conventional fluorophores. However, their use in biomedical applications is largely hindered due to strong absorption of short wavelength (< 600 nm) light by biological tissues/cells and feeble luminescence. Hence, it is important to develop new strategies to increase the long wavelength (red) emission efficiency. In this work, we report an effective strategy to improve the red luminescence efficiency of NaYF 4 :Yb/Ho/Mn upconversion nanophosphors by varying the reaction conditions. The influence of different synthesis parameters, such as solvent ratio, reaction temperature and reaction time, on the luminescence, crystal phase and morphology of the upconversion nanophosphors has been studied in detail and optimized. The improvement in the crystallinity of nanophosphors is claimed as the main origin for the increase in the red emission intensity. This work could pave way for the versatile use of these bright red emitting upconversion nanophosphors in biomedical applications.
We present a systematic study on the effect of surface ligands on the luminescence properties and colloidal stability of β-NaYF4:Yb,Er upconversion nanoparticles (UCNPs), comparing nine different surface coatings to render these UCNPs water-dispersible and bioconjugatable. A prerequisite for this study was a large-scale synthetic method that yields ~2 g per batch of monodisperse oleate-capped UCNPs providing identical core particles. These ~23-nm sized UCNPs display an upconversion quantum yield of ~0.35% when dispersed in cyclohexane and excited with a power density of 150 W cm−2. A comparison of the colloidal stability and luminescence properties of these UCNPs, subsequently surface-modified with ligand exchange or encapsulation protocols, revealed that the ratio of the green (545 nm) and red (658 nm) emission bands determined at a constant excitation power density depends on the surface chemistry. We demonstrate that the brightness of the upconverted luminescence is strongly affected by the type of surface modification, i.e., ligand exchange or encapsulation, yet hardly by the chemical nature of the ligand.
Upconversion nanoparticles: synthesis, surface modification and biological applications
Nanomedicine: Nanotechnology, Biology and Medicine, 2011
New generation fluorophores, also termed upconversion nanoparticles (UCNPs), have the ability to convert near infrared radiations with lower energy into visible radiations with higher energy via a non-linear optical process. Recently, these UCNPs have evolved as alternative fluorescent labels to traditional fluorophores, showing great potential for imaging and biodetection assays in both in vitro and in vivo applications. UCNPs exhibit unique luminescent properties, including high penetration depth into tissues, low background signals, large Stokes shifts, sharp emission bands, and high resistance to photo-bleaching, making UCNPs an attractive alternative source for overcoming current limitations in traditional fluorescent probes. In this review, we discuss the recent progress in the synthesis and surface modification of rare earth doped UCNPs with a specific focus on their biological applications.
Stability, dissolution, and cytotoxicity of NaYF4-upconversion nanoparticles with different coatings
Scientific Reports, 2022
Upconversion nanoparticles (UCNPs) have attracted considerable attention owing to their unique photophysical properties. Their utilization in biomedical applications depends on the understanding of their transformations under physiological conditions and their potential toxicity. In this study, NaYF4:Yb,Er UCNPs, widely used for luminescence and photophysical studies, were modified with a set of four different coordinatively bound surface ligands, i.e., citrate, alendronate (AA), ethylendiamine tetra(methylene phosphonate) (EDTMP), and poly(maleic anhydride-alt-1-octadecene) (PMAO), as well as silica coatings with two different thicknesses. Subsequently, the aging-induced release of fluoride ions in water and cell culture media and their cytotoxic profile to human keratinocytes were assessed in parallel to the cytotoxic evaluation of the ligands, sodium fluoride and the lanthanide ions. The cytotoxicity studies of UCNPs with different surface modifications demonstrated the good bioc...
Journal of Electronic Materials, 2016
We propose a new method to prepare Er 3+ /Yb 3+-codoped b-NaYF 4 upconversion nanoluminophores, allowing creation of single-crystalline-phase b-NaYF 4 : Er 3+ /Yb 3+ with concentrations up to 20 mol.% through a hydrothermal process. Using hexagonal-phase Y(OH) 3 precursors with different nanostructures (nanosheets, nanorods, nanotubes, etc.), one can obtain many types of onedimensional nano-NaYF 4 :Er 3+ /Yb 3+ materials and significantly improve the multiphase phenomenon, which is a common challenge facing many research groups that use a hydrothermal process for synthesis of NaYF 4 compounds. Upon near-infrared laser excitation at 976 nm, the obtained b-NaYF 4 :Er 3+ /Yb 3+ nanorods emit in green (2 H 11/2 , 4 S 3/2 fi 4 I 15/2) and red (4 F 9/2 fi 4 I 15/2) spectral regions with high intensity. Moreover, it is shown that one can change the luminescence integrated intensity ratio between the red and green emissions by varying the concentration and components of Er 3+ and Yb 3+ in the NaYF 4 host material. Comparative studies on the luminescence kinetics of the NaYF 4 :Er 3+ / Yb 3+ nanoluminophores were also conducted to explain the influence of Yb 3+ ion on the upconversion processes.