Humic acids, a major constituent of natural organic carbon resources, are naturally formed through the microbial biodegradation of animal and plant residues. Due to numerous physiologically active groups (phenol, carboxyl, and quinone), the biomedical applications of humic acid have been already investigated across different cultures for several centuries or even longer. In this work, sodium humate, the sodium salt of humic acid, is explored as phototheranostic agent for light‐induced photoacoustic imaging and photothermal therapy based on intrinsic absorption in the near‐infrared region. The purified colloidal sodium humate exhibits a high photothermal conversion efficiency up to 76.3%, much higher than that of the majority of state‐of‐the‐art photothermal agents including gold nanorods, Cu₉S₅ nanoparticles, antimonene quantum dots, and black phosphorus quantum dots, leading to obvious photoacoustic enhancement in vitro and in vivo. Besides, highly effective photothermal ablation of HeLa tumor is achieved through intratumoral injection. Impressively, sodium humate reveals ultralow toxicity at the cellular and animal levels. This work promises the great potential of humic acids as light‐mediated theranostic agents, thus expanding the application scope of traditional humic acids in biomedical field.

中文翻译：

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天然基于腐殖酸的光热敏剂

腐殖酸是天然有机碳资源的主要组成部分，是通过动植物残留物的微生物生物降解而自然形成的。由于有许多生理活性基团（苯酚，羧基和醌），腐殖酸的生物医学应用已经在不同文化中进行了数百年甚至更长的研究。在这项工作中，腐植酸钠是腐殖酸的钠盐，它被用作光热声处理剂，用于光诱导的光声成像和基于近红外区域内在吸收的光热疗法。纯化的胶体腐植酸钠具有高达76.3％的高光热转化效率，远高于包括金纳米棒，Cu ₉ S ₅在内的大多数最先进的光热剂的光热转化效率。纳米粒子，锑烯量子点和黑磷量子点，导致体内外明显的光声增强。此外，通过瘤内注射实现了高效的HeLa肿瘤光热消融。令人印象深刻的是，腐植酸钠在细胞和动物水平上显示出超低的毒性。这项工作有望将腐殖酸作为光介导的治疗药的巨大潜力，从而扩大传统腐殖酸在生物医学领域的应用范围。