A phosphomolybdenum blue nano-photothermal agent with dual peak absorption and biodegradable properties based on ssDNA in near-infrared photothermal therapy for breast cancer†

Photothermal therapy (PTT) stands as an emerging and promising treatment modality and is being developed for the treatment of breast cancer, prostate cancer, and a series of superficial tumors. This innovative approach harnesses photothermal agents (PTAs) that convert near-infrared light (NIR) energy into heat, efficiently heating and ablating localized lesion tissue. Notably, the low scattering of NIR-II (1000–1500 nm) band light within biological tissue ensures superior penetration depth, surpassing that of NIR I (700–900 nm) band light. Consequently, developing PTAs with excellent absorption performance and biocompatibility in the NIR-II band has attracted significant attention in photothermal therapy research. We successfully synthesized phosphomolybdenum blue (PMB) nanoparticles using single-strand DNA (ssDNA) as a template in this innovative study. Subsequently, we delved into this material's absorption characteristics and photothermal properties across the NIR-I and NIR-II spectral regions. Furthermore, we evaluated the therapeutic efficacy of PMB on 4T1 cells and tumor-bearing mouse models of breast cancer. Our findings revealed that PMB not only exhibits remarkable biocompatibility but also possesses stellar photothermal performance. Specifically, under 808 nm and 1064 nm laser irradiation, PMB achieved photothermal conversion efficiencies of 21.37% and 28.84%, respectively. Notably, compared to 808 nm laser irradiation, even when transmitting through a 2 mm thick tumor tissue homogenate, the 1064 nm laser irradiation maintained a robust tumor ablation effect. What's more, PMB possesses critical pH-responsive degradation properties. For instance, PMB nanoparticles degrade rapidly under physiological conditions (pH 7.2–7.4) while degrading slower in the acidic tumor microenvironment (pH 6.0–6.9). This unique characteristic significantly mitigates the systemic toxicity of PMB and enhances the safety of photothermal therapy implementation. Moreover, our study represents the first instance of utilizing ssDNA as a template for synthesizing a PMB nano photothermal agent and demonstrating its exceptional tumor thermal ablation efficacy. This groundbreaking work offers novel insights into the development of safe, efficient, and pH-responsive photothermal agents for cancer therapy.