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.