Progress in Metal-Based Nanomaterials for Photothermal Therapy in the Second Near-Infrared Window

Photothermal therapy (PTT), characterized by its non-invasiveness, minimal side effects, and potent anti-tumor efficacy, represents a promising alternative to conventional cancer treatments. PTT in the near-infrared-II (NIR-II) window (1000-1700 nm) obtains significant interest due to its lower energy dissipation, deeper penetration, and higher power safety windows than its counterparts conducted in other optical bands. Among those materials capable of coupling light and heat within the NIR-II window, metal-based nanomaterials bear a strong photothermal conversion capability that establishes them as highly effective and operationally convenient photothermal agents. However, biosafety risks and metabolic challenges pose critical limitations to their applications. This review focuses on the latest progress in metal-based nanoparticles for NIR-II responsive PTT and summarizes typical strategies for achieving multifunctional synergistic cancer treatment based on these materials. First, we review the mechanisms of photothermal effects and principal indicators for evaluating the PTT efficacy. Second, recent development strategies for metal and metal-compound nanoparticles for PTT and PTT-based treatments (e.g., photodynamic therapy, chemodynamic therapy, and chemotherapy, etc.) are systemically introduced. Finally, current challenges and opportunities of metal-based nanoparticles in NIR-II PTT are discussed, which helps the future development of metal-based nanoparticles for NIR-II PTT.