Customized Sized Manganese Sulfide Nanospheres as Efficient T1 MRI Contrast Agents for Enhanced Tumor Theranostics.

The impact of nanoparticle size on the effectiveness of magnetic resonance imaging (MRI) using sulfurized manganese nanoparticles (MnS@PAA) stabilized with polyacrylic acid (PAA) as a binder was thoroughly investigated. MnS@PAA nanoparticles of varying sizes were synthesized by altering the ratio of ethylene glycol (EG) to diethylene glycol (DEG) during the synthesis process. These nanoparticles exhibited a uniform size distribution and demonstrated high T₁ relaxation rates, along with a notable pH-responsive behavior. As the nanoparticle size increased, the T₁ relaxation rate decreased, indicating that size plays a crucial role in their MRI performance. Additionally, research has revealed that the efficiency of tumor uptake by these nanoparticles is size dependent. Specifically, MnS@PAA nanoparticles with a core size of 100 nm (MS₁₀₀) exhibited greater tumor accumulation and provided enhanced MRI contrast. Once within the acidic environment of a tumor, MS₁₀₀ decomposes into Mn²⁺ and H₂S. Mn²⁺ ions promote the generation of hydroxyl radicals, which leads to lipid peroxidation and induces ferroptosis. Concurrently, the release of H₂S inhibits catalase activity, resulting in elevated levels of hydrogen peroxide (H₂O₂), achieving a synergistic effect between chemodynamic therapy (CDT) and gas therapy. This study explores the influence of nanoparticle size on its potential applications as an MRI contrast agent and as a therapeutic agent in cancer treatment.