Spherical Nucleic Acids-Directed Cryosynthesis of Manganese Nanoagents for Tumor Imaging and Therapy

DNAzyme-based theranostic nanotechnologies that can respond to specific tumor pathophysiological parameters hold great promise for tumor diagnostics and effective treatments. However, their clinical translation is hindered by insufficient intracellular availability of essential metal cofactors required for DNAzyme activation. To overcome this limitation, we developed a temperature-controlled synthesis strategy for fabricating multifunctional DNA-templated manganese carbonate nanoparticles (DtMnP). The process involves three critical phases: (i) spherical nucleic acid hybrids, DNAzyme-functionalized AuNPs, serve as scaffolds for spatially controlled Mn²⁺ deposition through phosphate coordination, initiating heterogeneous nucleation of MnCO₃; (ii) rapid liquid nitrogen freezing induces nanoparticle growth along DNA templates; and (iii) lyophilization-mediated structural stabilization enables convenient long-term storage. The DtMnP exhibits pH-responsive dissolution, releasing 90% of Mn²⁺ within 60 min under tumor microenvironment conditions (pH 5.5). The released Mn²⁺ ion enables dual functionality: (i) superior magnetic resonance imaging (MRI) contrast of MCF-7 xenograft models with enhanced biosafety, and (ii) synergistic therapeutic efficacy through DNAzyme-mediated EGR-1 gene silencing (60% mRNA downregulation) combined with Mn²⁺-catalyzed Fenton reactions generating cytotoxic hydroxyl radicals (45% apoptosis in MCF-7 cells). The cryo-encapsulated DtMnP exemplifies a flexible and efficient approach for integrating various functional components into a single nanoparticle for tumor theranostic applications.