Trimetallic nitride endohedral fullerenes (TNT-EMF) have been recognized for their multifunctional capabilities in biomedical applications. Functionalized gadolinium-loaded fullerenes attracted much attention as a potential new nanoplatform for next-generation magnetic resonance imaging (MRI) contrast agents, given their inherent higher 1H relaxivity than most commercial contrast agents. The fullerene cage is an extraordinarily stable species which makes it extremely unlikely to break and release the toxic Gd metal ions into the bioenvironment. In addition, radiolabeled metals could be encapsulated in this robust carbon cage to deliver therapeutic irradiation. In this dissertation, we aim to develop a series of functionalized TNT-EMFs for MRI detection of various pathological conditions, such as brain cancer, chronic osteomyelitis, and gastrointestinal (GI) tract. As a general introduction, Chapter 1 briefly introduces recent progress in developing metallofullerenes for next-generation biomedical applications. Of special interest are MRI contrast agents. Other potential biomedical applications, toxicity, stability and biodistribution of metallofullerenes are also discussed. Finally, the challenges and future outlook of using fullerene in biomedical and diagnosis applications are summarized at the end of this chapter. The large carbon surface area is ideally suited for multiple exo-functionalization approaches to modify the hydrophobic fullerene cage for a more hydrophilic bio-environment. Additionally, peptides and other agents are readily covalently attached to this nanoprobe for targeting applications. Chapter 2 presents the functionalized metallofullerenes conjugated with interleukin-13 peptide exhibits enhanced targeting of U-251 glioblastoma multiforme (GBM) cell lines and can be effectively delivered intravenously in an orthotopic GBM mouse model. Chapter 3 shows, with the specific targeting moiety, the functionalized metallofullerenes can be applied as a non-invasive imaging approach to detect and differentiate chronic post-traumatic osteomyelitis from aseptic inflammation. Fullerene is a powerful antioxidant due to delocalization of the π-electrons over the carbon cage, which can readily react with free radicals and subsequently delivers a cascade of downstream possessions in numerous biomedical applications. Chapter 4 investigates the antioxidative and anti-inflammatory properties of functionalized Gd3N@C80. This nanoplatform would hold great promise as a novel class of theranostic agent in combating oxidative stress and resolving inflammation, given their inherent MRI applications. In chapter 5, Gd3N@C80 is modified with polyethylene glycol (PEG) for working as MRI contrast agents for GI tract. The high molecular weight can prevent any appreciable absorption through the skin or mucosal tissue, and offer considerable advantages for localized agents in the GI tract. Besides the excellent contrast capability, the PEGylated-Gd3N@C80 exhibits outstanding radical scavenging ability, which can potentially eliminate the reactive oxygen species in GI tract. The biodistribution result suggests this nanoplatform can be worked as the potential contrast agent for GI tract at least for 6 hours. A novel amphiphilic Gd3N@C80 derivative is discussed in Chapter 6. It has been noticed for a long time the functionalization Gd3N@C80 contrast agents have higher relaxivity at lower concentrations. The explanation for the concentration dependency is not fully understood. In this work, the amphiphilic Gd3N@C80 derivative is used as the model to investigate the relationship between the relaxivity and concentration of the Gd-based fullerenes. Click chemistry has been extensively used in functionalization due to the high efficiency and technical simplicity of the reaction. Appendix A describes a new type of Sc3N@C80 derivative conducted by employing the click reaction. The structure of Sc3N@C80-alkynyl and Sc3N@C80- alkynyl-benzyl azide are characterized by NMR, MALDI-TOF, UV-Vis, and HPLC. The high yield of the click reaction can provide access to various derivatives which have great potential for application in medical and materials science. The functionalization and characterizations of Ho3N@C80 derivatives are reported in Appendix B. The contrast ability of Ho3N@C80 is directly compared with Gd3N@C80. The Ho-based fullerenes can be performed as the radiotherapeutic agents; the leaching study is performed to test the stability of carbon cage after irradiation. Appendix C briefly shows a new method to develop Gd3N@C80 based targeting platform, which can be used as the probe for chronic post-traumatic osteomyelitis. / PHD