Nanoscale Magnetic Graphitic Nano- and Microcapsules: From Structural Design to Theranostic Applications

Magnetic graphitic nanocapsules (MGNCs) are a new class of multifunctional nanoscale theragnostic platforms that combine magnetic activity with the chemical stability and programmable surface properties of graphitic carbons. The core–shell nanostructure is generally constructed of Fe-, Co-, Ni-, or alloy-based magnetic nanoparticles embedded in graphitic carbon layers, which allows for simultaneous imaging, magnetic targeting, and therapeutic activities. The magnetic behavior, relaxivity, photothermal conversion, interfacial interactions, and biological performance are greatly affected by the nanoscale dimension, shell thickness, degree of graphitization, and defect density. The magnetic core controls the saturation magnetization and MRI contrast enhancement, while the graphitic shell offers chemical durability, programmable porosity, and efficient heat generation under external stimulation. This review critically discusses the nanoscale structure–property–performance relationships of MGNCs, emphasizing the effect of synthesis parameters including precursor selection, temperature, carbon source, and graphitization conditions on core–shell morphology, magnetic properties, and therapeutic efficiency. The multifunctional applications of MGNCs in magnetic resonance imaging (MRI), photothermal therapy, photodynamic therapy, and drug delivery are reviewed from mechanistic and biological views, including cellular internalization, biodistribution, and clearance pathways. Furthermore, it points out crucial problems such as nanoscale engineering, long-term biocompatibility, biodegradability, and scalable production. In summary, MGNCs present great promise for next-generation image-guided and minimally invasive nanomedicine applications; however, further developments are needed for successful clinical translation.