Hybrid morphologies of paramagnetic manganese-based nanoparticles as theranostics

Paramagnetic nanoagents are attractive due to their indispensability in imaging and therapy applications. Their application has transcended magnetic resonance imaging (MRI) contrast agents (CAs) to multifunctional diagnostics and theranostics. The large surface area and ease of functionalization of nanoparticles (NPs) allow facile attachment of ligands. The composite component can enrich their diagnostic abilities and bestow therapeutic potentialities depending on the function of each unit. These advances have resulted in new imaging modalities, therapeutic processes, precision, and efficient imaging-guided therapy procedures. Combining diagnostic and therapeutic techniques into a single 'theranostic' platform is an intriguing area of biomedical research. With their innate physicochemical characteristics and biological effects, transition metal manganese (Mn)-based nanoparticulate systems have evolved as multifunctional nanoplatforms for meeting rigorous biomedical criteria, thereby producing diverse morphologies. Morphology is one of the essential physicochemical properties that affects the biodistribution, diagnosis, and treatment performance of biological nanoagents. Despite these significant advances, no review has collated the shapes of the most commonly-reported Mn-based theranostics in a single account. Herein, theranostic Mn-based nanohybrids classified by morphologies are discussed. Their synthesis methods are outlined, properties summarized, and morphology's significance, performance, and influence on their use as theranostics are examined. The toxicity and biocompatibility of the recent Mn-based NPs are summarized, and the design considerations section provides several key factors to evaluate when engineering biologically suitable theranostics. Finally, relevant challenges and guidelines for producing clinically applicable nanohybrids are enumerated. It is envisaged that the present review will contribute to the future research and development of Mn-based theranostics and other types of theranostics.