Reversible Thermochromic Nanoparticles Composed of a Eutectic Mixture for Temperature-Controlled Photothermal Therapy.

Photothermal therapy (PTT) is an effective approach to cancer therapy. However, the high temperature during the therapy increases the damage to surrounding normal tissues. Thermochromic material, which exhibits temperature-activated color change and optical absorption, is a promising photothermal agent for precisely temperature-controlled PTT. Nevertheless, the construction of nanosized thermochromic particles with an appropriate transition temperature (44-47 °C) is still a great challenge. Here, thermochromic nanoparticles with the transition temperature at 45 °C based on a leuco dye-developer-solvent system are developed for thermostatic photothermal tumor therapy. Below the temperature, the nanoparticles take a dark green color to absorb light and convert it into heat efficiently. Once the temperature reaches the transition point, the colored nanoparticles switch to a colorless state, maintaining the temperature at the predefined level and allowing deeper light penetration. The autoregulated nanoparticles exhibit a prominent therapeutic effect for the tumor without destroying normal tissues.