Application of upconversion nanoparticles as a thermal sensor for biological tissue

Abstract

The paper shows the possibility of simultaneous registration of the temperature of nanoparticles embedded in the fat layer and temperature-induced phase transitions in the fat layer. The luminescence spectra of upconversion particles (UCNPs) were measured and analyzed in a wide temperature range: from room to physiological and further to a hyperthermic temperature resulting in tissue morphology change. Typical samples thickness of adipose tissue was 0.5 mm. The sample temperature varied between 25 °C and 60 °C. The temperature dependence of the UCNPs luminescence intensity from UCNPs deposited onto the sample surface (1 layer) and from UCNPs deposited between two layers of abdominal adipose tissue was recorded. In the course of adipocyte 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 high-temperature transition is recorded most well. The obtained results confirm a high sensitivity of the luminescent UCNPs to the temperature variations within tissues and show a strong potential for the controllable tissue thermolysis.