Size- and Wavelength-Selective Optical Heating in Mie-Resonant Silicon Nanospheres for Nanothermometry and Photothermal Applications

The photothermal heating properties of perfectly spherical crystalline silicon nanoparticles having Mie resonances in the visible range are studied under different illumination wavelengths by using the Raman scattering peak as a nanothermometer. Analytical calculations reveal that the magnetic quadrupole (MQ) Mie mode is the most suitable mode for photothermal heating. The experimentally obtained size and illumination wavelength dependence of the temperature rise agrees quantitatively with numerical simulations, and the heating efficiency reaches up to 381 K/(mW/μm2) when the illumination wavelength of 633 nm matches the MQ resonance. Conversely, tuning the illumination wavelength to a relatively nonabsorbing mode, such as the electric dipole (ED) mode, can significantly reduce the heating effect. In this context, the ED mode functions as a practically heating-less nanoantenna, promoting the surface-enhanced fluorescence of nearby dye molecules, while high-Q modes, e.g., MQ and electric quadrupole (EQ) modes, serve as an optical heating platform. Furthermore, the photothermal heating and Raman thermometry of silicon nanoparticles in water and in cancer cells are demonstrated.