Daria V. Pominova

Spectroscopic research of upconversion nanomaterials based on complex oxide compounds doped with rare-earth ion pairs: Benefit for cancer diagnostics by upconversion fluorescence and radio sensitive methods/Spektroskopische Untersuchung von mit Ionenpaaren Seltener Erden dotierten Upconversion-Nanokompositen: Nutzen für die Krebsdiagnostik durch Upconversion-Fluoreszenz und strahlungssensitive Methoden

Abstract Background: Highly photochemically stable nanoparticles, in which upconversion luminescence can be excited – so-called upconversion nanocrystals (UC-NCs) – exhibit widely separated (up to 500 nm) narrow luminescence bands in the visible (VIS) region located far from the excitation near-infrared (NIR) laser radiation, and thus can be more easily identified compared to organic luminophores and semiconductor nanoparticles. Due to a deep penetration of exciting infrared (IR) radiation, the absence of parasitic fluorescence of biomolecules and the absence of phototoxicity and photobleaching upon near IR excitation, UC-NCs can be efficiently used as fluorescent probes in biological studies and fluorescence diagnostics (FD). The doping of such nanoparticles with Gd3+ ions provides the additional possibility of combining fluorescence visualization with magnetic resonance imaging, which will considerably improve the sensitivity of diagnostics of cancer tumors even in the early stages. Materials and methods: We studied the upconversion characteristics of inorganic nanoparticles made of different materials doped with rare-earth ion (REI) pairs Yb3+-Er3+ and Yb3+-Tm3+ as functions of the concentration and composition of a dopant at different excitation intensities. Matrices chosen for doping were complex polycrystalline oxide rare earth compounds Gd2GeMoO8, La4Gd10B6Ge2O34, and Gd11SiP3O26 which permit the introduction of significant concentrations of the activator luminescence ions (Yb3+, Er3+ and Tm3+), synthesized by solid-phase reaction methods from corresponding oxides. The final product was obtained by combined precipitation of initial components from aqueous solutions followed by the annealing of hydroxide mixtures and grinding. The redistribution of the intensity of the 550 nm 2H11/2, 4S3/2→4I15/2 and 650 nm 4F9/2→4I15/2 upconversion luminescence bands in Er3+ was investigated depending on matrices, dopants, and the laser power density. The quantum yield and lifetime of upconversion luminescence were determined for individual electronic transitions, which were used to optimize the composition of dopants in matrices. Results: Based on the results obtained, the matrix La4Gd10B6Ge2O34 is most effective for the upconversion process in the VIS spectrum. Doping nanoparticles by REI pairs Yb3+-Er3+ and Yb3+-Tm3+, each has its advantages. REI pair Yb3+-Er3+ is good for energy transfer in the green and/or red part of the spectrum as well as for the FD and can be used for a further energy transfer to the photosensitizers at photodynamic therapy (PDT). REI pair Yb3+-Tm3+ transform the infrared radiation in the blue region of the spectrum, which is also suitable for FD and PDT and additional intensive energy conversion in NIR will allow for deep tissue imaging. Conclusion: The investigated complex polycrystalline oxide compounds are promising as diagnostic agents for biological tissues visualization by fluorescence, light scattering, and nuclear magnetic resonance imaging. Zusammenfassung Hintergrund: Photochemisch hochstabile Nanopartikel, in denen Upconversion-Lumineszenz angeregt werden kann – die sogenannten Upconversion-Nanokomposite (UC-NCs) – weisen eng begrenzte, schmale Lumineszenz-Banden (bis 500 nm) im sichtbaren Wellenlängenbereich auf, die weit genug von der Anregungs-Laserstrahlung im Nahinfrarot (NIR)-Bereich entfernt sind und somit leichter gegenüber organischen Luminophoren und Halbleiternanopartikeln zu identifizieren sind. Durch die hohe Eindringtiefe des infraroten (IR) Anregungslichtes und das Fehlen parasitärer Fluoreszenz durch Biomoleküle sowie Phototoxizitäts- und Photobleechingeffekte im Bereich der IR-Anregung können UC-NCs effizient als Fluoreszenzsonden für biologische Untersuchungen und die Fluoreszenzdiagnostik (FD) eingesetzt werden. Die Dotierung solcher Nanopartikel mit Gd3+-Ionen bietet zusätzlich die Möglichkeit der Kombination von Fluoreszenz-Visualisierung und Magnetresonanz-Bildgebung, was die Empfindlichkeit der Diagnostik von Tumoren auch in frühen Stadien deutlich verbessert. Material und Methoden: Wir untersuchten die Upconversion-Eigenschaften von anorganischen Nanopartikeln aus unterschiedlichen Materialien, die mit Ionenpaaren Seltener Erden dotiert wurden (Yb3+-Er3+ und Yb3+-Tm3+), und zwar in Abhängigkeit von der Konzentration und Zusammensetzung des Dotands bei unterschiedlichen Anregungsenergien. Als Grundsubstanzen für eine Dotierung wurden komplexe polykristalline Oxidverbindungen Seltener Erden ausgewählt (Gd2GeMoO8, La4Gd10 B6Ge2O34, und Gd11SiP3O26), die die Einführung signifikanter Konzentrationen der Aktivator-Lumineszenz-Ionen (Yb3+, Er3+ und Tm3+) gestatten – synthetisiert durch Festphasenreaktionsmethoden aus korrespondierenden Oxiden. Das Endprodukt wurde durch die kombinierte Ausfällung der anfänglichen Komponenten aus wässriger Lösung und anschließendes Glühen und Mahlen der Hydroxidgemische erzeugt. Die Umverteilung der Intensität der 550 nm 2H11/2, 4S3/2→4I15/2 und 650 nm 4F9/2→4I15/2 Upconversion-Lumineszenz-Banden wurde in Abhängigkeit von den Grundstoffen, Dotanden und der Laserleistungsdichte untersucht. Die Quantenausbeute und die Lebensdauer der Upconversion-Lumineszenz wurden für einzelne elektronische Übergänge bestimmt, die zur Optimierung der Dotanden-Zusammensetzung verwendet wurden. Ergebnisse: Wie sich zeigte, ist die La4Gd10B6Ge2O34-Matrix im sichtbaren Spektralbereich am effektivsten für den Upconversion-Prozess. Beide dotierenden Ionenpaare Seltener Erden (Yb3+-Er3+ und Yb3+-Tm3+) haben ihre Vorteile. Das Yb3+-Er3+-Ionenpaar ist gut für die Energieübertragung im grünen und/oder roten Spektralbereich als auch für die FD und kann für eine weitere Energieübertragung auf den Photosensibilisator während der photodynamischen Therapie (PDT) verwendet werden. Das Yb3+-Tm3+-Ionenpaar verwandelt die IR-Strahlung im blauen Bereich des Spektrums, was ebenfalls für die FD und PDT geeignet ist und eine zusätzliche intensive Energieumwandlung in NIR bewirkt, was ein Imaging tiefer Gewebeschichten erlaubt. Fazit: Die untersuchten komplexen polykristallinen Oxidverbindungen sind als diagnostische Mittel zur Darstellung biologischen Gewebes mittels Fluoreszenz, Lichtstreuung und Magnetresonanz-Bildgebung geeignet.

Pulsed periodic laser excitation of upconversion luminescence for deep biotissue visualization

Emission spectral properties and quantum efficiency of upconversion particles NaYF4, SrF2, LaF3, BaF2 и CaF2, doped with rare earth ions pair Yb3+–Er3+ were studied using continuous wave (CW) and pulsed periodic excitation modes in the near infrared (NIR) spectral range. Analysis of the obtained results showed that the intensity ratio of upconversion luminescence in green and red spectral ranges depends on excitation pulse duration. Thus, by changing the pulse duration the spectral properties of upconversion luminescence can be controlled. Crystals with higher phonon energy are more sensitive to the change of pumping mode. Interpretation of results was performed on the rate equation model basis. Using numerical methods for all energy levels involved in the upconversion process the population and depopulation dynamics were obtained with respect to the duration of the excitation pulses. It was shown that about 30 ms was required for the complete population of 4F9/2 state, from which the luminescence in the red spectral range occurs. When the pulse duration was less than 30 ms, the 4F9/2 population did not reach a steady state and the intensity of the luminescence in the red part of the spectrum was reduced. The theoretical dependence of the upconversion luminescence intensity in the green and red ranges of the excitation pulse duration for NaYF4:Yb0.2–Er0.02 composition was obtained and demonstrates good agreement with the experimental results.

Upconversion microparticles as time-resolved luminescent probes for multiphoton microscopy: desired signal extraction from the streaking effect

Abstract. The great interest in upconversion nanoparticles exists due to their high efficiency under multiphoton excitation. However, when these particles are used in scanning microscopy, the upconversion luminescence causes a streaking effect due to the long lifetime. This article describes a method of upconversion microparticle luminescence lifetime determination with help of modified Lucy–Richardson deconvolution of laser scanning microscope (LSM) image obtained under near-IR excitation using nondescanned detectors. Determination of the upconversion luminescence intensity and the decay time of separate microparticles was done by intensity profile along the image fast scan axis approximation. We studied upconversion submicroparticles based on fluoride hosts doped with Yb3+-Er3+ and Yb3+-Tm3+ rare earth ion pairs, and the characteristic decay times were 0.1 to 1.5 ms. We also compared the results of LSM measurements with the photon counting method results; the spread of values was about 13% and was associated with the approximation error. Data obtained from live cells showed the possibility of distinguishing the position of upconversion submicroparticles inside and outside the cells by the difference of their lifetime. The proposed technique allows using the upconversion microparticles without shells as probes for the presence of OH− ions and CO2 molecules.

Bioimaging with controlled depth using upconversion nanoparticles

The study of bioimaging with controlled depth using upconversion nanoparticles under near-infrared excitation was performed in this work. Monte Carlo simulation was performed to determine optimal distance between the fiber - source of laser radiation, and the receiving fiber for obtaining the signal from maximal depth in biological tissue. Also theoretical modeling of the spatial distribution of diffusely scattered radiation inside the tissue depending on wavelength is presented. Penetration depth for wavelengths corresponding to the upconversion luminescence was calculated. Experimental modeling was carried out on phantoms of biological tissues simulating their scattering properties as well as accumulation of the investigated nanoparticles doped with rare earth ions. Measurements were performed using NaGdF4 nanoparticles doped with Yb3+, Er3+ and Tm3+ rare earth ions, which demonstrated several luminescence bands from the blue (475nm) to the near-infrared (800 nm) regions of the spectrum under 980 nm excitation. The different penetration depth of various wavelengths in biotissue allows us to estimate the depth from which the signal was obtained using luminescence intensity ratio (LIR). Due to non-linearity of upconversion process, pumping power dependences of luminescence intensity was taken into account. The number of involved photons for each spectral band was estimated and intensity ratio of emission bands was calculated. Based on calculations and experimental measurements, the theoretical and experimental luminescence intensity ratio for different depths was estimated. The experimental study was performed on biological tissue phantoms containing Lipofundin® with red blood cells and has shown good agreement with calculations. The use of theoretically calculated LIR allows us to solve the inverse problem and estimate the depth from which the signal was obtained.

Multispectral imaging technique for skin grafts’ functional state assessment

The development of express method for assessing the state of skin graft by the spectroscopic properties of tissue components involved in the healing of the affected skin or healing of skin grafts was carried out in present work. The proposed method for assessing the state of the skin by the spectroscopic properties of tissue components (using photosensitizers, fluorescent dyes (methylene blue and IcG) and nanophotosensitizers aluminum phthalocyanine nanoparticles (NP-AlPc) applied locally) will evaluate the physiological condition of the skin and assess the degree and rate of engraftment or rejection while also controlling several biochemical and physiological parameters in the entire graft, or the whole area of the skin lesions. Such parameters include the oxygenation of hemoglobin in the tissue microvasculature; the blood supply level; blood flow and lymph flow; assessment of intracellular metabolism; assessment of the cellular respiration type (aerobic/anaerobic).To assess the extent of inflammation the spectrally sensitive to biological environment nanoparticles of aluminum phthalocyanine (NP-AlPc) were also used.

Experimental modeling of local laser hyperthermia using thermosensitive nanoparticles absorbing in NIR

In this work we investigated the use of composite crystalline core/shell nanoparticles LaF3:Nd3+(1%)@DyPO4 for fluorescence-based contactless thermometry, as well as laser-induced hyperthermia effect in optical model of biological tissue with modeled neoplasm. In preparation for this, a thermal calibration of the nanoparticles luminescence spectra was carried out. The results of the spectroscopic temperature measurement were compared to infrared thermal camera measurements. It showed that there is a significant difference between temperature recorded with IR camera and the actual temperature of the nanoparticles in the depth of the tissue model. The temperature calculated using the spectral method was up to 10 °C higher.

Multifunctional upconversion nanoparticles based on NaYGdF4 for laser induced heating, non-contact temperature sensing and controlled hyperthermia with use of pulsed periodic laser excitation

For clinical application in photothermal therapy the nanoparticles should be efficient light-to-heat converters and luminescent markers. In this work, we investigate upconversion nanoparticles with NaYxGd1-xF4 (x=0-1) host lattice as self-monitored thermo-agents for bioimaging and local laser hyperthermia with real-time temperature control. The ability of non-contact temperature sensing using NaYxGd1-xF4 on one hand and laser induced heating on the other hand was shown. It was found, that the heat conversion luminescence efficiency is strongly affected by the concentration ratio of Gd3+ to Y3+ ions in host lattice. The optimal composition among the studied is NaY0.4Gd0.4Yb0.17Er0.03 with luminescence efficiency of 3.5% under 1 W/cm2 pumping power. Higher Gd3+ concentrations lead to higher heating temperature, but also to the decrease of the luminescence intensity and the accuracy of the ratiometric temperature determination. It was also shown that the optimization of Yb3+ doping concentration is one of the possible ways for optimization of the conditions of laser induced photothermal effects. Experimental in vitro study of hyperthermia with use of upconversion nanoparticles on HeLa and C6 cell lines was performed. The investigated nanoparticles are capable of in vitro photothermal heating, luminescent localization and thermal sensing.

Synthesis and Luminescence Characteristics of LaF 3 :Yb:Er Powders Produced by Coprecipitation from Aqueous Solutions

Hydrated lanthanum fluoride powders, both undoped, and doped with erbium and ytterbium fluorides (to a total content of 6–28 mol %), of the general formula RF3 · nH2O (n = 0.30 ± 0.01), crystallizing in the hexagonal system, were obtained by coprecipitation from aqueous solutions of the corresponding nitrates by the interaction with hydrofluoric acid. The dehydration is completed at 380°C. At 600°C, the concentrated solid solution decomposes to precipitate a phase with the structure of orthorhombic YF3. The efficiency of the upconversion luminescence of the powders, excited at a wavelength of 974 nm, is low.

ВИЗУАЛИЗАЦИЯ НАНОЧАСТИЦ LaF3, ДОПИРОВАННЫХ Nd3+, ДЛЯ БИОИМИДЖИНГА В БЛИЖНЕМ ИНФРАКРАСНОМ ДИАПАЗОНЕ ПО АП-КОНВЕРСИОННОЙ ЛЮМИНЕСЦЕНЦИИ ПРИ МИКРОСКОПИИ С МУЛЬТИФОТОННЫМ ВОЗБУЖДЕНИЕМ

Ryabova A.V.1, Keevend K.2, Tsolaki E.3, Bertazzo S.3, Pominova D.V.1, Romanishkin I.D.1, Grachev P.V. 1, Makarov V.I.1, Burmistrov I.A.4, Vanetsev A.S.1,6, Orlovskaya E.O.1, Baranchikov A.E.5, R hn M.6, Sildos I.6, Sammelselg V.6, Loschenov V.B.1, Orlovskii Y.V.1,6 General Physics Institute of the Russian Academy of Sciences, Moscow, Russia Swiss Federal Laboratories for Materials Science and Technology (Empa), St. Gallen, Switzerland University College London (UCL), London, United Kingdom Lomonosov Moscow State University, Moscow, Russia Kurnakov Institute of General and Inorganic Chemistry RAS, Moscow, Russia Institute of Physics, University of Tartu, Tartu, Estonia

Synthesis and study of M 1−x−y Yb x Er y F 2+x+y (M = Ca, Ba) efficient up-conversion luminophores for biomedical applications

Study of phase composition, morphology and up-conversion luminescence of ytterbium- and erbium-doped barium and calcium fluoride nanopowders has revealed the influence of their synthetic conditions on their up-conversion luminescence energy yields.