Synthesis Of DNA-Mn Nanoflower And Its Study In Magnetic Resonance Imaging Of Tumor

DNA nanoflower(DNF)as a DNA-inorganic hybrid nanomaterial has attracted widespread attention due to its excellent serum stability and high load capacity of DNA.At present,almost all DNFs were prepared by Mg2+-involved rolling circle amplification(RCA).However,other metal ions-involved RCA reactions for constructing DNFs were rarely reported.In this thesis,Mn²⁺-mediated RCA was utilized to prepare the DNA-Mn hybrid nanoflower(DMNF).The structural characteristics,functional features and magnetic resonance imaging(MRI)performance of DMNF were studied systematically.The main research work is summarized as follows:In the first chapter,the development of DNA nanostructures was reviewed.Focusing on DNFs,their synthetic methods and recent biomedical applications were summarized.Subsequently,the progress of manganese-based nanomaterials in the field of MRI was introduced.In the end,the research significance and content were proposed.In the second chapter,Mn²⁺-mediated rolling circle amplification was introduced to construct DNA-Mn nanoflower(DMNF).The DMNF was obtained by the self-assembly of generated long strand DNA and manganese pyrophosphate in RCA reaction.By tuning the Mn²⁺concentration and reaction time,DMNF achieved the size control from nanoscale to microscale.During the formation of DMNF,bovine serum albumin,which was an additive protein for maintaining the bioactive of DNA polymerase,could be encapsulated into the DMNF through the coordination between Mn²⁺and carboxylates of protein residues.The results suggested DMNF could act as a potential protein carrier.In the third chapter,the AS 1411-DMNF targeting MCF-7 cells(human breast cancer cells)was prepared by coding AS 1411 aptamer complementary sequences on the circular DNA template.It was verified that the aptamer-encoded DMNF possessed the excellent tumor targeting through the confocal microscopy imaging and flow cytometry taking C28/i2 cells as the control group.Meanwhile,the aptamer could improve the uptake of DMNF by cancer cells.In the fourth chapter,the aptamer-encoded DMNF was explored as an acid-responsive probe for enhanced MRI of tumor mice.It was verified that Mn2PPi framework of DMNF could decompose and release free Mn²⁺under acidic conditions using the scanning electron microscope and inductively coupled plasma-optical emission spectroscopy.The MRI capabilities of DMNF under neutral and acidic conditions were characterized by MRI system,respectively,indicating that DMNF possessed brighter magnetic resonance imaging signals and higher relaxation rates.In vivo imaging experiments confirmed that the aptamer-encoded DMNF had better tumor targeting and magnetic imaging capabilities.In the last chapter,we summarized the research progress of DMNF and forecasted its potential biomedical application.Mn²⁺-mediated RCA was utilized to prepare DMNF for tumor-targeted enhanced MRI.The DMNF exhibited possibilities for chemodynamic therapy and immunity.