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.
Delivery and spatial localization of upconversion luminescent microparticles [Y2O3:Yb, Er] (mean size ∼1.6 μm) and quantum dots (QDs) (CuInS2/ZnS nanoparticles coated with polyethylene glycol-based amphiphilic polymer, mean size ∼20 nm) inside rat skin was studied in vivo using a multimodal optical imaging approach. The particles were embedded into the skin dermis to the depth from 300 to 500 μm through microchannels performed by fractional laser microablation. Low-frequency ultrasound was applied to enhance penetration of the particles into the skin. Visualization of the particles was revealed using a combination of luminescent spectroscopy, optical coherence tomography, confocal microscopy, and histochemical analysis. Optical clearing was used to enhance the image contrast of the luminescent signal from the particles. It was demonstrated that the penetration depth of particles depends on their size, resulting in a different detection time interval (days) of the luminescent signal from microparticles and QDs inside the rat skin in vivo. We show that luminescent signal from the upconversion microparticles and QDs was detected after the particle delivery into the rat skin in vivo during eighth and fourth days, respectively. We hypothesize that the upconversion microparticles have created a long-time depot localized in the laser-created channels, as the QDs spread over the surrounding tissues.
The luminescence spectra of a polymer film with embedded upconversion nanoparticles (UCNPs) were measured through 0.1-0.3 mm adipose tissue layer at heating in a wide temperature range. Heating and application of optical clearing agents improved intensity of UCNP fluorescence significantly.
The luminescence spectra of upconversion nanoparticles (UCNPs) imbedded in fat tissue were measured in a wide temperature range, from room to human body and further to hyperthermic temperatures. The two types of synthesized UCNP [NaYF4:Yb3+, Er3+] specimens, namely, powdered as-is and embedded into polymer film, were used. The results show that the luminescence of UCNPs placed under the adipose tissue layer is reasonably good sensitive to temperature change and reflects phase transitions of lipids in tissue cells. The most likely, 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 phase transitions of lipids were observed as the changes of the slope of the temperature dependence of UCNP luminescence intensity. The obtained results confirm a high sensitivity of the luminescent UCNPs to the temperature variations within tissues and show a strong potential for providing a controllable tissue thermolysis.
Delivery of upconversion microparticles [Y2O3:Yb, Er] and quantum dots (CuInS2/ZnS coated with PEG-based amphiphilic polymer) into rat skin using the fractional laser microablation has been studied in vivo. Luminescence spectroscopy, optical coherence tomography, confocal microscopy, and histochemical analysis were used for visualization of nanoparticles in microchannels. Results have shown that the upconversion microparticles are detected more efficiently in comparison with the quantum dots. The fluorescence intensity of the inserted upconversion microparticles is higher, when the Omnipaque™ was applied as a skin optical clearing agent. The fluorescent images of upconversion nanoparticle distribution indicate the advantage of particle delivery into skin by ultrasound.
KEYWORDS: Tissues, Nanoparticles, Luminescence, Temperature metrology, Laser tissue interaction, In vitro testing, Tissue optics, Semiconductors, Absorption, Process control
Temperature dependence of the fluorescence spectrum of ZnCdS nanoparticles introduced into 200-500 μm thick fat tissue slices in vitro was studied. The heating of the samples from the room to physiological temperature results in stronger (in depth) and faster tissue morphology change. This can help to detect location of nanoparticles during fat cell photothermolysis.
Internal temperature of biological tissues was measured in real-time mode under close-to-in-vivo conditions. Research technique is based on the comparison of the temperature inside the biological object and changes in the fluorescence spectra of temperature-sensitive fluorescent semiconductor ZnCdS nanoparticles introduced into muscle tissue. The temperature dependence of the ratio of maximum fluorescence intensities of the nanoparticles and the biological tissue was approximately linear.
The effect of heavy metal ions on the fluorescence of semiconductor ZnCdS nanoparticles in albumin solution was studied. It was found that the fluorescence intensity of ZnCdS nanoparticles depends on the albumin concentration in the solution. Interacting with ZnCdS nanoparticles, heavy metals differently affect the fluorescence intensity of the nanoparticles. Copper ions induce fluorescence quenching, cadmium ions increases the fluorescence intensity, and zinc ions do not affect the fluorescence intensity. ZnCdS nanoparticles are most sensitive to copper ions. Albumin enhances the effect of copper ions. The results on the influence of heavy metals on the fluorescence intensity of ZnCdS nanoparticles can be used to create a selective sensor for determination of copper ions in proteins using fluorescence quenching.
The temperature dependence of the fluorescent spectra of ZnCdS nanoparticles placed into a biological tissue has been
investigated. It is shown that the fluorescence peak of the nanoparticles is shifted towards longer wavelengths, and
fluorescence quenching is observed during heating the biological tissue until its denaturation. ZnCdS nanoparticles are
suitable for measuring the temperature of biological nanoobjects under photothermolysis.
The effect of glucose on fluorescence of synthesized ZnCdS nanoparticles in the presence of glucose oxidase or in a mixture of glucose oxidase and peroxidase has been investigated. Behavior of fluorescence characteristics of ZnCdS nanoparticles with nonstabilized surface and coated with polymer shell is compared. It has been shown that, for uncoated ZnCdS nanoparticles, hydrogen peroxide formed by glucose oxidation with glucose oxidase causes static quenching of the nanoparticle fluorescence. A quenching mechanism is proposed in which surface centers of fluorescence, which include cationic vacancies, trap oxygen ions supplied by hydrogen peroxide. It has been shown that the linear Stern–Volmer plot has no threshold within the investigated concentrations of glucose. The sensitivity of ZnCdS nanoparticles to glucose, determined from the slope of linear Stern–Volmer plot, is maximum for polymer-coated nanoparticles and is 12.2 ml/mg . With peroxidase, there is a threshold concentration of glucose (160 μM) below which the nanoparticles become insensitive to glucose.
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