Design of novel photothermal conversion nanoparticles integrated with temperature self-response ability based on thermal-enhanced NIR to NIR luminescence

The development of photothermal therapy (PTT) agents possessing temperature self-response ability and working in the deep tissues is an urgent need for noninvasive cancer treatment. Herein, a nanocomposite material hexagonal phase NaLuF₄: Yb³⁺/Nd³⁺@SiO₂@Cu₂S is successfully constructed for the purpose of meeting the above demands. Under the irradiation of 980 nm near-infrared (NIR) light, the prepared nanocrystals (NCs) exhibit good photothermal conversion capacity and ultrasensitive temperature sensing properties along with remarkable resolution. The optical thermometry is realized by the fluorescence intensity ratio of Nd³⁺: ⁴F_j (j = 7/2, 5/2, and 3/2) levels, of which the NIR emission intensities are strongly enhanced with the increasing temperature due to the phonon-assisted energy transfer mechanisms between Yb³⁺ and Nd³⁺. As the excitation and emission wavelength of the sample are all located in the biological window, its penetration depth in the biological tissues can be reached to 8 mm. The adsorptive Cu₂S NCs on the surface of NaLuF₄: Yb³⁺/Nd³⁺@SiO₂ provide the required light-to-heat conversion capacity, which has been investigated in detail through the laser-irradiated and bactericidal experiment respectively. These findings provide a feasible strategy to design high-performance PTT agents integrated with precise temperature self-measurement function for deep-tissue therapy.