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Photothermal therapy (PTT) has attracted increasing interest as a complementary method to be used alongside conventional therapies. Despite a great number of studies in this field, only a few have explored how temperatures affect the outcome of the PTT at nanoscale. In this work, we study the necrosis/apoptosis process of cancerous cells that occurs during PTT, using a combination of local laser heating and nanoscale fluorescence thermometry techniques. The temperature distribution within a whole cell was evaluated using fluorescence lifetime imaging microscopy during laser-induced hyperthermia. For this, gold nanorods were utilized as nanoheaters. The local near-infrared laser illumination produces a temperature gradient across the cells, which is precisely measured by nanoscale thermometry. This allows one to optimize the PTT conditions by varying concentration of gold nanorods associated with cells and laser power density. During the PTT procedure, such an approach enables an accurate determination of the percentages of apoptotic and necrotic cells using 2D and 3D models. According to the performed cell experiments, the influence of temperature increase during the PTT on cell death mechanisms has been verified and determined. Our investigations can improve the understanding of the PTT mechanisms and increase its therapeutic efficiency while avoiding any side effects.

Lead‐free halide perovskites is a novel class of environment‐friendly nonlinear optical materials, that already demonstrate high potential for second harmonics generation (SHG). Here a synthesis protocol is optimized to create single‐crystal CsGeI3 nanoparticles (NPs) supporting optical Mie resonances that efficiently convert infrared light to visible both via lasing and SHG mechanisms. Such high‐quality resonant NPs allow us to achieve up‐conversion lasing in the broadband excitation wavelength (1200–1520 nm), which is accompanied by efficient spectrally tunable SHG with intensity comparable with that for lasing depending on temperature. Experimental and theoretical study of linear and nonlinear optical properties of CsGeI3 material in the form of high‐quality thin film and NPs of different sizes reveal that coupling incident light with a magnetic dipole resonance leads to a strong enhancement of SHG by one order of magnitude. As a result, the study provides a novel strategy where individual NPs can support both up‐conversion lasing and SHG in a broad range of excitation wavelengths. [ABSTRACT FROM AUTHOR]