Upconverting nanoparticles as primary thermometers and power sensors

Luminescence thermometry is a spectroscopic technique for remote temperature detection based on the thermal dependence of the luminescence of phosphors, presenting numerous applications ranging from biosciences to engineering. In this work, we use the Er3+ emission of the NaGdF4/NaGdF4:Yb3+,Er3+/NaGdF4 upconverting nanoparticles upon 980 nm laser excitation to determine simultaneously the absolute temperature and the excitation power density. The Er3+ 2H11/2→4 I15/2 and 4 S3/2→4 I15/2 emission bands, which are commonly used for thermometric purposes, overlap with the 2 H9/2 →4 I13/2 emission band, which can lead to erroneous temperature readout. Applying the concept of luminescent primary thermometry to resolve the overlapping Er3+ transitions, a dual nanosensor synchronously measuring the temperature and the delivered laser pump power is successfully realized holding promising applications in laser-supported thermal therapies.publishe

High resolution fluorescence imaging of cancers using lanthanide ion-doped upconverting nanocrystals

During the last decade inorganic luminescent nanoparticles that emit visible light under near infrared (NIR) excitation (in the biological window) have played a relevant role for high resolution imaging of cancer. Indeed, semiconductor quantum dots (QDs) and metal nanoparticles, mostly gold nanorods (GNRs), are already commercially available for this purpose. In this work we review the role which is being played by a relatively new class of nanoparticles, based on lanthanide ion doped nanocrystals, to target and image cancer cells using upconversion fluorescence microscopy. These nanoparticles are insulating nanocrystals that are usually doped with small percentages of two different rare earth (lanthanide) ions: The excited donor ions (usually Yb3+ ion) that absorb the NIR excitation and the acceptor ions (usually Er3+, Ho3+ or Tm3+), that are responsible for the emitted visible (or also near infrared) radiation. The higher conversion efficiency of these nanoparticles in respect to those based on QDs and GNRs, as well as the almost independent excitation/emission properties from the particle size, make them particularly promising for fluorescence imaging. The different approaches of these novel nanoparticles devoted to "in vitro" and "in vivo" cancer imaging, selective targeting and treatment are examined in this reviewJ.A.C. is a Concordia University Research Chair in Nanoscience and is grateful to Concordia University for financial support of his research. J.A.C. and F.V. are grateful for financial support from the Natural Sciences and Engineering Research Council (NSERC) of Canada. R.N. is grateful for NSERC financial support through the Alexander Graham Bell Graduate Scholarship Program. B.F.Z. is grateful to les Fonds Québécois de Recherche sur la Nature et les Technologies (FQRNT) for financial support through the Graduate Scholarship Program. This work was also supported in part by the Universidad Autónoma de Madrid and Comunidad Autónoma de Madrid (Projects CCG087-UAM/MAT-4434 and S2009/MAT-1756), by the Spanish Ministerio de Educación y Ciencia (MAT 2010–16161). EMR acknowledges financial support from Fundación Alfonso Martín Escudero and Marie Curie IOF Fellowship Program (project 274404 LUNAMED

Nanoparticles for highly efficient multiphoton fluorescence bioimaging

In this paper, we demonstrate for the first time that the new class of fluoride-based inorganic upconverting nanoparticles, NaYF4:Er3+, Yb3+, are the most efficient multiphoton excited fluorescent nanoparticles developed to date. The near-infrared-to-visible conversion efficiency of the aforementioned nanoparticles surpasses that of CdSe quantum dots and gold nanorods, which are the commercially available inorganic fluorescent nanoprobes presently used for multiphoton fluorescence bioimaging. The results presented here open new perspectives for the implementation of fluorescence tomography by multiphoton fluorescence imaging

Structural investigation and Anti-Stokes emission of scandium oxide nanocrystals activated with trivalent erbium

The structural and emission (Stokes and anti-Stokes) properties of Sc2O3: Er3+ nanocrystals doped with 0.1, 1, and 10 mol % Er3+ were investigated. The nanocrystalline powders were characterized using X-ray scattering as well as transmission and scanning electron microscopy. The samples showed a very porous, open microstructure with the particles having a narrow distribution of sizes (10-60 nm). Furthermore, the mechanisms responsible for the anti-Stokes emission (lambda(exc) = 980 nm) were elucidated. We observed that the processes responsible for populating the green (H-2(11/2), S-4(3/2)) and red (F-4(9/2)) emitting states were dependent upon the concentration of the dopant ion. In 0.1 mol % nanocrystalline Sc2O3: Er3+, upconversion was determined to occur via excited state absorption while in the 10 mol % sample, energy transfer upconversion was the dominant mechanism. An enhancement of the red anti-Stokes emission from the F-4(9/2) --> I-4(15/2) transition was observed in Sc2O3: Er3+ nanocrystals as a function of Er3+ concentration. This was the result of two independent processes responsible for directly populating the F-4(9/2) state and bypassing the green emitting levels (H-2(11/2) and S-4(3/2)). Furthermore, the red enhancement was found to be more pronounced compared to identically doped Y2O3: Er3+ nanocrystals. An explanation for this phenomenon is presented and discussed

PEG-capped, lanthanide doped GdF3 nanoparticles: luminescent and T-2 contrast agents for optical and MRI multimodal imaging

A facile method for the synthesis of water dispersible Er3+/Yb3+ and Tm3+/Yb3+ doped upconverting GdF3 nanoparticles is reported. Strong upconversion emissions are observed in the red (for Er/Yb doped) and near-infrared (for Tm/Yb doped) regions upon laser excitation at 980 nm. The PEG coating ensures a good dispersion of the system in water and reduces the radiationless de-excitation of the excited states of the Er3+ and Tm3+ ions by water molecules. The r(2) relaxivity values are quite high with respect to the common T-2-relaxing agents (22.6 +/- 3.4 mM(-1) s(-1) and 15.8 +/- 3.4 mM(-1) s(-1) for the Tm/Yb and Er/Yb doped samples, respectively), suggesting that the present NPs can be interesting as T-2 weighted contrast agents for proton MRI purpose. Preliminary experiments conducted in vitro, in stem cell cultures, and in vivo, after subcutaneous injection of the lanthanide-doped GdF3 NPs, indicate scarce toxic effects. After an intravenous injection in mice, the GdF3 NPs localize mainly in the liver. The present results indicate that the present Er3+/Yb3+ and Tm3+/Yb3+ doped GdF3 NPs are suitable candidates to be efficiently used as bimodal probes for both in vitro and in vivo optical and magnetic resonance imaging

Luminescence spectroscopy of Er³⁺ doped inorganic nanocrystals : an investigation into their upconversion properties

This thesis presents a detailed investigation into the spectroscopic properties of inorganic nanocrystals doped with trivalent rare earth ions. We focus on their upconversion luminescence, emission of radiation at higher energy than the pump wavelength, and evaluate the fundamental mechanisms of upconversion in the nanocrystal. We evaluate the spectroscopic properties of sesquioxide nanocrystals doped with trivalent erbium (M 2 O 3 :Er 3+ , where M = Y, Lu, or Sc) prepared by the propellant synthesis technique. Characteristic green, red, and near-infrared Er 3+ emission is observed following excitation with 488 nm in all samples under investigation. The overall luminescence intensity of the sesquioxide nanocrystals is lower compared to the microcrystalline material (bulk) as a result of the presence of high vibrational energies, 1500 and 3350 cm -1 , due to adsorbed CO 3 2- and OH - anions, respectively, which significantly increase the rate of multiphonon relaxation. The garnet (Gd 3 Ga 5 O 12 :Er 3+ ) nanocrystals, however, have considerably less surface adsorbed species, which consequently increases the luminescence intensity drastically. The upconversion of red (n exc = 650 nm) and near-infrared (n exc = 800 or 980 nm) radiation into UV, blue, green, and red emission is studied for Er 3+ ions doped in various sesquioxide (Y 2 O 3 , Lu 2 O 3 , and SC 2 O 3 ) and garnet (Gd 3 Ga 5 O 12 ) nanocrystals over a wide range of temperatures and dopant concentration is investigated. We present, for the first time, upconversion in a trivalent rare earth (RE 3+ ) doped nanocrystalline material, specifically Y 2 O 3 :Er 3+ . We show that replacing the Y 3+ cation has significant consequences on the upconversion. The upconverted luminescence of Lu 2 O 3 :Er 3+ nanocrystals have intensities that are 100x greater compared to identically doped nanocrystalline Y 2 O 3 :Er 3+ . Furthermore, Sc 2 O 3:Er 3+ nanocrystals show an enhanced red emission, which is greater than Y 2 O 3 :Er 3+ nanocrystals (with identical Er 3+ concentration) due to the smaller unit cell resulting in increased interaction between Er 3+ ions. The upconversion is observed to be dependent on the method of preparation. We explore nanocrystalline Y 2 O 3 :Er 3+ prepared via the propellant synthesis technique and a controlled hydrolysis synthesis (or wet chemical synthesis) where we observed quite diverse upconversion behavior attributed to the vastly different morphological properties of the two different nanocrystalline materials. Additionally, we investigate the effect of Yb 3+ co-doping on the upconversion luminescence of Y 2 O 3 :Er 3+ nanocrystals prepared via the two distinct synthesis routes, and observe a significant change in the mechanisms of upconversion. In the sesquioxides, the upconversion properties of the nanocrystalline material are diverse from the bulk counterpart. Finally, we attempt to ascertain if any spectroscopic changes occur in nanosized Lu 2 O 3 :Nd 3+ , Y 2 O 3 :Sm 3+ and Y 2 O 3 :Dy 3+ prepared via combustion synthesis. In all cases, the size of the particles affects the luminescence behavio

Nd 3+ doped Gd 3 Sc 2 Al 3 O 12 nanoparticles: towards efficient nanoprobes for temperature sensing

International audienceDevelopment of contactless temperature-probing nanoplatforms based on thermosensitive near-infrared (NIR) light-emitting nanoparticles opens up new horizons for biomedical theranostics at a deep tissue level. Here, we report on the crystallinity and relative thermal sensitivity of NIR emitting Nd3+ doped Gd3Sc2Al3O12 (GSAG:Nd3+) nanoparticles synthesized by a solvothermal method. The obtained nanoparticles are well-crystallized, with sizes less than 100 nm, and can be dispersed in water without any additional functionalization. Upon excitation at 806 nm, the nanoparticles exhibit emission in the first and second biological optical transparency windows. The temperature sensing properties were evaluated from the luminescence intensity ratio of the thermally coupled emission lines corresponding to the R1, R2 Z5 transitions between the Stark sublevels of the 4F3/2 and 4I9/2 electronic states of Nd3+ in the physiological temperature range of 20-50 °C. GSAG:Nd3+ nanoparticles exhibit a maximal relative thermal sensitivity of 0.20% °C-1, higher than that of YAG:Nd3+ nanoparticles used as a control, due to the difference in the crystal field of the host matrices. A higher synthesis temperature in the range of 300-400 °C was also provided to improve the crystallinity of the GSAG:Nd3+ nanoparticles which results in a higher relative thermal sensitivity. Our results demonstrate the potential of GSAG:Nd3+ nanoparticles as luminescence nanothermometers and emphasize the interest of the GSAG matrix itself, which with the presence of Gd, could lead to multimodal diagnostic applications in nanothermometry and magnetic resonance imaging (MRI)