The luminescence spectra of upconversion NaYF4:Yb, Er nanoparticles located under layers of biological tissue of different thickness were experimentally obtained. Luminescence of the particles was excited by laser radiation with a wavelength of 980 nm through a layer of biological tissue. The radiation power was 0.5 W. Luminescence was collected using a collimator with an aperture of 0.15 located at a distance of 20 cm from the sample. The spectra were recorded using a QE 65000 spectrometer (Ocean Optics, US). As the tissue samples, layers of rat skin, muscle and adipose tissue were used. The thicknesses of the samples were varied in the range of 1-2 mm. Distortions of the luminescence spectra resulting from its attenuation in an absorbing-scattering sample are shown. The dependences of distortions on the type and thickness of the sample, as well as on the luminescence wavelength, are obtained. The results obtained are important in determining the temperature of nanoparticles from the luminescence spectra, since the distortions of the spectra lead to an error in determining the temperature.
The present work demonstrates the temperature dependences of the spectral characteristics of the skin measured in vitro. Changes in the spectral characteristics of the rat skin upon skin heat treatment at elevated temperatures have been characterized. The spectra were recorded with a stepwise increase in temperature in the range of 25-70ºC, as well as in the process of keeping the sample at a fixed temperature for 60 min. The dynamics of the changes in collimated transmittance of rat skin is shown to be temperature-dependent. It is assumed that the changes in spectral characteristics of the skin might be caused by changes in the size and refractive index of the scatterers.
When administered into the bloodstream, upconversion nanoparticles used in therapeutic / diagnostic purposes can affect red blood cells. In this work, using light optical microscopy, we show that the removal of citrate groups from the surface of NaYF4: Er3+ , Yb3+ nanoparticles synthesized by the hydrothermal method prevents the formation of large clod-like aggregates from a suspension of washed rat erythrocytes incubated with the nanoparticles. However, the tendency toward a change in cell shape with an increase in nanoparticles concentration is still manifested.
Temperature dependences of the spectral characteristics of the rat skin, muscle and fat tissues were obtained in vitro. The changes in the spectral characteristics of the rat skin subjected to 60 min thermal treatment at elevated (>40°C) temperatures have been characterized. The dynamics of the changes in collimated transmittance of rat skin at elevated temperature is shown to be temperature-dependent. It is assumed that the changes in spectral characteristics might be caused by changes in light scattering regime within the sample.
The excitation power dependence of upconversion luminescence intensity and temperature sensing characteristics are investigated in the NaYF4 : Er3 + , Yb3 + @ SiO2 particles synthesized in-house using a hydrothermal method. The effect of laser-induced heating of the upconversion particles is shown, which introduces distortions in the measured power and temperature dependences of the upconversion luminescence. We propose a technique for calibrating the temperature dependence of upconversion particle luminescence, which should improve the accuracy of temperature measurements. The technique is based on the stabilization of upconversion particles temperature, which provides the suppression of laser-induced heating of upconversion particles.
The present work demonstrates the visualization of the intracellular distribution of upconversion nanoparticles (UCNPs) by microscopy with excitation in the NIR spectral range and detection of upconversion luminescence in the VIS range. The cell viability is scored for cytotoxic effects of UCNPs at dark and light exposed conditions. Non-functionalized UCNPs incubated with the cells are found to be endocytosed by cells. The obtained results confirm a high sensitivity of the luminescent UCNPs to the concentration variations within cells. UCNPs are promising alternatives to traditional fluorescent labels for cell imaging and possess prominent potentials in biological and clinical applications.
Upconversion nanoparticles (UCNPs) are of interest as novel luminescent probes for numerous applications in nanobiophotonics. The small size of UCNPs enables the particles to overcome biological barriers, thereby ensuring a deep penetration into the tissues and accumulation in a number of organs. In addition, particles are known to possess high surface chemical reactivity as well as a large surface-tovolume ratio, which affect their biocompatibility. In this paper, we present data of the dark toxicity of uncoated UCNPs in the course of their interaction with tissues and organs. It was found inflammatory reaction that developing in the organism when UCNPs are introduced under the skin. The signs of damage and necrosis in all layers of the skin were not observed. The dense connective tissue capsule was formed around the particles through a week after their administration. The particles do not diffuse and dissolve, but remain at the introduction site. UCNPs cause an inflammatory reaction in skin, in a week the skin site, where particles were administrated, is almost not seen. The changes in blood supply and blood circulation in the organs were developed in 2 days mainly. This in turn led to insignificant dystrophic changes. All changes were reversible and disappear or their degree of severity decreases after 7 days after the administration of the particles. The particles enter the total blood flow, but they did not show a pronounced toxicity.
The luminescence spectra of upconversion nanoparticles (UCNPs) and ZnCdS nanoparticles (ZnCdSNPs) were measured and analyzed in a wide temperature range: from room to human body and further to a hyperthermic temperature resulting in tissue morphology change. The results show that the luminescence signal of UCNPs and ZnCdSNPs placed within the tissue is reasonably good sensitive to temperature change and accompanied by phase transitions of lipid structures of adipose tissue. The most likely that the multiple phase transitions are associated with the different components of fat cells, such as phospholipids of cell membrane and lipids of fat droplets. In the course of fat cell heating, lipids of fat droplet first transit from a crystalline form to a liquid crystal form and then to a liquid form, which is characterized by much less scattering. The results of phase transitions of lipids were observed as the changes in the slope of the temperature dependence of the intensity of luminescence of the film with nanoparticles embedded into tissue. The obtained results confirm a high sensitivity of the luminescent UCNPs and ZnCdSNPs to the temperature variations within thin tissue samples and show a strong potential for the controllable tissue thermolysis.
The spectra of luminescence of ZnCdS nanoparticles (ZnCdS NPs) were measured and analyzed in a wide temperature range: from room to human body and further to a hyperthermic temperature resulting in tissue morphology change. The results show that the signal of luminescence of ZnCdS NPs placed within the tissue is reasonably good sensitive to temperature change and accompanied by phase transitions of lipid structures of adipose tissue. It is shown that the presence of a phase transition in adipose tissue upon its heating (polymorphic transformations of lipids) leads to a nonmonotonic temperature dependence of the intensity of luminescence for the nanoparticles introduced into adipose tissue. This is due to a change in the light scattering by the tissue. The light scattering of adipose tissue greatly distorts the results of temperature measurements. The application of these nanoparticles is possible for temperature measurements in very thin or weakly scattering samples.
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