Julia G. Konyukhova

Fluorescent ZnCdS nanoparticles for glucose sensing

Abstract. 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.

ZnCdS nanoparticles as nanobiosensors to determine denaturation of tissue

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.

Temperature dependence of the fluorescence spectrum of ZnCdS nanoparticles

The temperature sensitivity of the spectral characteristics of ZnCdS nanoparticles both stabilized and coated with polyacrylic acid is compared. It is shown that the luminescence of the nanoparticles has two temperature-dependent parameters, namely, the intensity and the peak position. Variations in these parameters are due to the distortion of the energy states of luminescent surface defects. Aggregation of the nanoparticles does not distort obtained dependencies. Temperature sensitivity is higher for the nanoparticles coated with a layer of polyacrylic acid.

Glucose and temperature sensitive luminescence ZnCdS nanoparticles

The effect of glucose on fluorescence characteristics of synthesized ZnCdS nanoparticles in glucose oxidase solution has been investigated. It has been shown that, on addition of glucose, the nanoparticle fluorescence is quenched. Dynamics of fluorescence quenching with increasing glucose concentration was observed. Threshold sensitivity of recording of glucose concentration has been 0,25 mg/ml. So the presented effect opens the facilities for application of synthesized ZnCdS nanoparticles for the glucose control in bodyfluids.

Features of recording and calculating XEOL spectra

Fluorescence techniques of recording EXAFS spectra are considered: XEOL and fluorescence EXAFS. The main causes of spectra distortions induced by both experiment conditions and mechanisms of luminescences appearance under the action of synchrotron radiation. The algorithms of correction of experimental spectra to compensate for distortions are considered. By the example of alkali-halide crystals, it is demonstrated that, as the spectrum is recorded, radiationinduced transformations of the structure can occur in the sample. These transformations are not brought out in EXAFS spectra, but are detected by the XEOL method.

Fluorescent ZnCdS nanoparticles for nanothermometry of biological tissues

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.

Comparison of temperature sensing of the luminescent upconversion and ZnCdS nanoparticles

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.

Effect of luminescence transport through adipose tissue on measurement of tissue temperature by using ZnCdS nanothermometers

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.

Temperature sensing of adipose tissue heating with the luminescent upconversion nanoparticles as nanothermometer: in vitro study

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.

Controlling of upconversion nanoparticle luminescence at heating and optical clearing of adipose tissue

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.