Metallic oxide nanocrystals with near-infrared plasmon resonance for efficient, stable and biocompatible photothermal cancer therapy

Abstract

Photothermal therapy is regarded as one of the most promising cancer treatment technologies due to its negligible side effects and fast operation. However, its therapeutic efficacy is still limited by the lack of cost-effective photostable and biocompatible therapeutic agents with efficient light absorption in the biological window. Here, taking MoO₂ as an example, we propose oxide nanocrystals (NCs), with both a metallic electronic structure and near-infrared (NIR) plasmon resonance, for efficient, stable and biocompatible photothermal cancer therapy. Monoclinic MoO₂ NCs with good crystallinity were fabricated through the combination of laser ablation in liquid and solvothermal synthesis. The as-synthesized NCs showed intensive local surface plasmon resonance (LSPR) absorption at 800–1000 nm, the NIR biological window, due to their metallic electronic structure and oxide dielectric function. This unique NIR LSPR characteristic leads to excellent photothermal performance, i.e., the maximum temperature elevation was found to be up to 37.5 °C with a MoO₂ NC concentration of 0.05 mg mL⁻¹ under 808 nm laser irradiation. Moreover, MoO₂ solution is highly photostable, as it exhibits stable irradiation-induced temperature elevation of about 14.3 °C even after four temperature elevation cycles. As a photothermal therapy agent against 4T1 cancer cells, MoO₂ NCs exhibit not only good biocompatibility, but also excellent tumor inhibition effects. The highest inhibition rate was up to 80.45%, and the average tumor volume was 2.73 times smaller than normal growth 14 days after the treatment. The results prove that MoO₂ NCs exhibiting NIR LSPR can act as an effective agent for photothermal cancer therapy with great photostability and biocompatibility.