Metal nanoparticles in cancer theranostics: from synthesis to tumor microenvironment-responsive applications

Cancer poses a major threat to human health, and conventional treatments (such as surgery, radiotherapy (RT), and chemotherapy) are often associated with significant toxic side effects, poor targeting, and drug resistance. In recent years, nanomedicine, an emerging interdisciplinary field, has provided novel strategies for cancer diagnosis and therapy by enabling precise drug delivery and multifunctional integration. Among various nanoplatforms, metal nanoparticles (MNPs) have become a research hotspot due to their unique physicochemical properties, including optical characteristics, catalytic activity, and surface modifiability. This article systematically explores the role of MNPs in cancer therapy. It first outlines their classification and synthesis strategies. Subsequently, it analyzes their innovative applications in tumor diagnosis, RT, chemotherapy, and immunotherapy. A key focus is placed on elucidating how MNPs exploit distinctive features of the tumor microenvironment - such as acidic pH, elevated reactive oxygen species (ROS) levels, and high glutathione (GSH) concentrations - to achieve responsive and targeted drug delivery. Finally, the main challenges currently faced in this field are analyzed. This review aims to provide theoretical guidance and technical references for the rational design and clinical translation of MNPs.