Laser-assisted Preparation Of Manganese Oxide-based Nanomaterials And Their Biomedical Performance

In recent years,manganese oxide-based nanomaterials have broad application prospects in biomedical fields(including bioimaging,biosensing and tumor therapy)based on the advantages of tunable structure,various valence states,unique magnetic properties and biosafety.However,as the field of nanomedicine continues to broaden,the performance of manganese oxide-based nanomaterials gradually fails to meet the application requirements,and the regulation of their structure,morphology and valence state is a hot research topic.In this thesis,because of the extreme nonequilibrium conditions of localized high temperature,high pressure environment and rapid quenching provided by laser synthesis in liquids technique,the size morphology regulation,defect introduction and material composite of various manganese oxide nanomaterials were realized.In addition,this thesis presented a reasonable hypothesis on the mechanism of laser preparation of manganese oxide nanomaterials in liquids through the experimental results and theoretical analysis.Meanwhile,the intrinsic connection between the structure and properties of manganese oxide-based nanomaterials was explored in depth to lay the foundation for their wide application in biomedical fields.The main research content and the results obtained in this paper are as follows.1.We synthesized ultrathin MnOx nanobelts(NBs)with rich oxygen vacancies by laser irradiation in ammonia,and investigated their oxidase mimic activities.Based on the catalytic reaction kinetic test results,the MnOx NBs had a Michaelis constant of 0.0087 mM and a maximum reaction velocity of 6.04 × 10-7 M/s,indicating that the MnOx NBs had a high affinity for the chromogenic substrate 3,3’,5,5’tetramethylbenzidine(TMB)and an extremely fast reaction velocity,which were significantly better than that of Mn3O4 NPs and most of the reported oxidase mimics.Meanwhile,combining experimental and theoretical analyses,we proposed a hypothesis for the synthesis mechanism of MnOx NBs:that is,Mn3O4 NPs were broken into MnOx nanofragments under laser irradiation,followed by the reorientation and growth of the nanofragments under the synergistic effect of NH4+,alkaline liquid-phase and laser.Finally,MnOx NBs were generated.Furthermore,combined with the results of density functional theory calculations,we analyzed that the high activity of MnOx NBs originated from three aspects:ultrathin layered structure,unique negative charge layer,and laser-induced rich oxygen vacancies.They conferred highly exposed active sites,high affinity to the TMB and low oxygen adsorption energy to MnOx NBs.Meanwhile,due to the inhibitory effect of glutathione on oxidase mimics,we developed a glutathione assay with low cost,rapid detection and high sensitivity.This work highlights the advantages of the laser synthesis in liquids technique for the preparation of highly active nanozymes.2.We obtained Mn3O4 nanoparticles(NPs)with grain boundaries by laser irradiation in water.Then,based on the galvanic replacement reaction between PtCl42ions and Mn3O4 NPs with grain boundaries,and the subsequent reduction process,we successfully prepared Mn3O4/Pt nanocomposites as nanozymes,named Pt colloidosomes(Cs).Experimental and theoretical calculations showed that the grain boundaries not only enhanced the adsorption of PtCl42-ions on the surface of Mn3O4 NPs and increased the rate of galvanic replacement reaction,but also promoted the uniform distribution of Mn2+ ions on the surface of Mn3O4 NPs as galvanic replacement reaction sites.These led to the high-density deposition of ultrasmall size Pt NPs on the surface of Mn3O4 NPs,which effectively broadened the light absorption band of Pt Cs.Firstly,by testing the enzyme-like catalytic activity and catalytic reaction kinetics of Pt Cs under near-infrared(NIR)light irradiation,we demonstrated that NIR light helps to enhance the catalytic activity of peroxidase-like activity,oxidase-like activity and self-cascade catalytic activity of Pt Cs.Second,the comparison of the enzyme-like activities of the groups under different experimental conditions verified that the activity enhancement of Pt Cs by NIR light not only originated from the temperature rise of Pt Cs due to the photothermal effect.Then,combining the results of photocurrent tests,density functional theory calculations and finite difference in time domain simulations,we demonstrated that NIR light can effectively excited Pt Cs to generate hot electrons,which in turn promoted the elevated enzyme-like activity of Pt Cs.Finally,in vivo and in vitro experiments further verified the superior anti-tumor ability and biocompatibility of Pt Cs guided by MR imaging and photothermal imaging.This work experimentally verifies the contribution of hot electrons in enzyme-like catalytic reactions and provides new ideas for the future design of photo-enhanced nanozymes.3.On the basis of the laser ablation in liquids technique,laser irradiation in liquids technique and galvanic replacement reaction,we prepared Mn3O4/PtOx nanocomposites(NCs)for T1 MR imaging.Based on the in vivo and in vitro MR imaging results,the longitudinal relaxivity of Mn3O4/PtOx NCs could reach 20.48 mM-1 s-1,which is about 4 times that of commercial Gd-DTPA.Meanwhile,compared with Gd-DTPA,the MR signal-to-noise ratio of tumor sites in mice was significantly higher and the MR imaging time was longer after intravenous injection of Mn3O4/PtOx NCs,which verified the excellent MR contrast performance of Mn3O4/PtOx NCs.Combining the experimental results and the theoretical model,we deduced that the high MR imaging performance of Mn3O4/PtOx NCs originates from two points:first,the porous nanostructure promoted the increase of the specific surface area of the material,which increased the number of Mn2+ coordinated with water protons;second,the payload of PtOx nanoclusters effectively prolonged the rotational correlation time of the material.These two together contributed to the contrast performance of Mn3O4/PtOx NCs.In addition,Mn3O4/PtOx NCs could be used as computed tomography(CT)contrast agents to achieve bimodal contrast.This work experimentally verifies the possibility of noble metal loading for enhancing the performance of MR contrast agents,and provides a new idea for the development of high-performance MR contrast agents.4.By using the laser fragmentation in liquids technique,we prepared oxygen vacancy-rich MnO nanodots(NDs)using methanol as the liquid-phase.We demonstrated the good cellular safety of MnO NDs by cytotoxicity experiments,the results of urine metabolism and organ retention experiments verified the renal clearance of MnO NDs,and the good biocompatibility of MnO NDs was further verified by tissue sections and blood biochemical analysis.Based on the reported theoretical advantages of antiferromagnetic materials for ultrahigh-field MR imaging and the favorable effect of oxygen vacancies on water molecule adsorption in MR imaging,we initially tried MnO NDs for in vivo ultrahigh-field(14.1 T)MR imaging,and the results showed that MnO NDs could significantly improve the in vivo MR imaging signal-to-noise ratio in mice.The possibility of MnO NDs as an ultrahighfield MR contrast agent in this work is being further explored.