Study of energy transfer processes between the rare earth ions in NaGdF4 nanoparticles tri-doped with rare earth ions Yb3+, Er3+ and Ho3+ or Tm3+ was carried out. The luminescence spectra in short-wave infrared and visible ranges were investigated. It was shown that Er3+ → Ho3+ energy transfer leads to Ho3+ luminescence increase. Both Er3+ and Ho3+ luminescence peaks were observed in short-wave infrared range. For Er3+ and Tm3+ co-doped nanoparticles it was hard to separate luminescence peaks in SWIR. However, both Er3+ and Tm3+ luminescence peaks were observed in visible range. We attribute this effects to Tm3+ → Er3+ energy transfer which occurs due to overlap of Er3+ and Tm3+ luminescence bands in short-wave infrared range which leads to Tm3+ luminescence decrease. This hypothesis was confirmed by study of β-NaGdF4 tri-doped with Yb3+, Er3+ and Tm3+ luminescence spectra during heating. The intensity of Tm3+ luminescence increased during heating due to non-resonant nature of Yb3+ →Tm3+ energy transfer and the shape of spectra changed.
The limited penetration of laser radiation into biological tissue prevents the widespread distribution of photodiagnostics (PD) and photodynamic therapy (PDT) methods to clinical practice. We have investigated several approaches for PD and PDT of deep-seated tumors: 1. Stereotactic biopsy cannula with a laser spectroscopic control. Special fiber ports for long-term installation in the tumor removal area were developed in order to cause tumor cells to migrate not into the depth of brain but along the fibers with occasional laser irradiation for PD and PDT. The fibers are coated with a special compound containing photosensitizer (PS) and nutrients for cancer cells. 2. Neurosurgical aspirator with the function of video-fluorescence and spectroscopic analysis system. More than 500 patients with various types of brain tumors were operated on using fluorescent navigation based on 5-aminolevulinic acid (5-ALA) induced protoporphyrin IX (Pp IX) fluorescence under laser excitation in red spectral range. 3. Diagnostics and navigation of tumors when fluorescence is excited in the red and near infrared ranges. We used indocyanine green (ICG) as near infrared dye to observe blood and lymph vasculature of laboratory animals. This method could be useful while examining tumor bed and adjacent area. 4. Joint action of radiopharmaceuticals and PS based on Cherenkov radiation. Cell death by PDT mechanism via Pp IX excitation by Cherenkov radiation in mitochondria during 18F-fludeoxyglucose decay. This idea achieved good results on rats with C6 glioma. The results of using this approach with chlorin e6 PS in comparable doses are negative. 5. Action through photodynamic inactivation of tumor-associated macrophages and microglia. Idea of minimally invasive method for determining macrophage (microglia) phenotype and their polarization in tumors and their immediate vicinity in situ. This would allow evaluating the effectiveness of the treatment, including PDT. The most promising results were obtained with Pp IX and aluminum phthalocyanine nanoparticles. Studies have been conducted on experimental animals with grafted tumors and, in part, on cancer patients in the clinic.
Current paper presents the results of the chlorine e6 (Ce6) study on 2D and 3D models of FaDu cells culture. The 2D model or monolayer was used for investigation of Ce6 distribution within individual cells and their organelles. The 3D model or multicellular tumor spheroids were used for estimation of cells’ metabolic processes by the investigation of the Ce6 fluorescence distribution within spheroid's layers and Ce6 fluorescence lifetime. It was shown that 3D cell cultures and Сe6 allows estimating the cells’ metabolic processes better than in 2D monolayer cell cultures. Also, this model allows estimating the photodynamic effect depending on the proximity to the surface of different areas inside the heterogeneous 3D structure.
The Yb3+-Tm3+-doped NaGdF4 upconversion nanoparticles were studied as contactless nanothermometers for the first biological tissue transparency window under 980 nm excitation. The single hexagonal phase NaGdF4:Yb3+-Tm3+ nanoparticles were synthesized by solvothermal technique. The influence of dopants concentration and pumping power density on thermal sensitivity and temperature resolution of obtained nanoparticles was analyzed. It was shown, that an increase of Yb3+ doping concentration leads to a strong increase in near-infrared Tm3+ luminescence intensity, which corresponds to transitions 3F2-3H6, 3F3-3H6, 3H4-3H6 and could be used for thermometry. The measured efficiency of upconversion luminescence for 80% of Yb3+ and 2% of Tm3+ doped nanoparticles was 5.0% compared to 0.2% efficiency for 30% of Yb3+ and 0.5% of Tm3+ doped nanoparticles. Laser induced heating of synthesized nanoparticles with ratiometric temperature measurement was studied. The increase of pumping power density negatively affected the sensitivity, but increased the accuracy of measurement due to the increased near-infrared luminescence. In addition, the comparison of different wavelengths for ratiometric thermal calibration was performed. It was shown, that the use of 680-720 nm luminescence peak to 730-750 nm valley intensity ratio for thermometry promotes significant enhancement of thermal sensitivity and temperature resolution. Thermal sensitivity of 4%∙C-1 and temperature resolution of 0.6˚C in 30-36˚C region were obtained for NaGdF4 nanoparticles doped with 80% of Yb3+ and 2% of Tm3+.
Current paper presents the results of the optical neurosystem research for intracranial implantation targeted on phototheranostics of deep-lying brain tumors. Brain tumors treatment is a complicated multistage process, and currently there is a need for the user-friendly fiber optic toolkit that could allow carrying out multiple diagnostics and therapy of such neoplasms type without additional surgical intervention. The optical neurosystem developed in the framework of this study is based on the scaffold with the internal optical fiber structure placed into the tumor bed and designed for diagnostic and therapeutic laser radiation delivery. Such neurosystem, along with specific photosensitive agent application will provide malignant cells diagnostics by the fluorescent signal and permanent monitoring of processes occurring in the probed area by means of fiber optic probe with emitting and receiving fibers connected with laser source and spectrometer, respectively. The created neurosystem could be used to direct the growth of randomly proliferated deep lying brain tumor cells along the scaffold fibers towards the extracranial surface where malignant cells could be registered, identified and therapeutically affected by photodynamic action. A set of preliminary experiments devoted to spectral-optical evaluation of brain tissue properties was performed. The research of the scaffold and its inner fiber optical structure was carried out on the model samples of brain tissue phantom and in vitro on C6 glioblastoma cell line. Obtained results are being discussed.
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.
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.
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.
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.
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