Biomedical Diagnosis And Therapy Based On Functional Nucleic Acids And Black Phosphorus Nanomaterials

During the past few decades,cancer has became the leading cause of human death and one of the most important public health issues.For this reason,researchers have made great efforts in finding and developing methods for tumor diagnosis and treatment.Compared with proteins,nucleic acid biomarkers show greater advantages in the field of early cancer diagnosis,mainly because the nucleic acid has the characteristics of amplification capability,flexible designability and good stability.It is easy to build a universal platform for the detection of multiple nucleic acid biomarkers.A variety of nucleic acid amplification strategies have provided good basis for highly sensitive and selective detection of tiny changes in nucleic acid expression which provides a possibility for early cancer diagnosis.With the rapid development of biomedicine and nanotechnology,a variety of treatment methods with distinctive advantages have effectively supplemented the traditional tumor treatment methods.The continuous emergence of two-dimensional nanomaterials with special physical/chemical properties and ideal structure has accelerated the development of multifunctional nanotheranostic platform in the field of biomedicine.New ideas for the optimization of tumor diagnosis and treatment are inspired by improving the therapeutic performance of two-dimensional materials through doping,or designing multifunctional nanotheranostic platform with intelligent response to the tumor microenvironment.In view of this,this work focus on designing a multiple-stage HCR signal amplification system for high sensitivity detection and accurate intracellular localization of mi RNA biomarkers,and developing a BPNs-based multifunctional nanocomposite for tumor therapy and antibacterial application.In Chapter 1,these early cancer diagnosis methods were reviewed firstly based on nucleic acid biomarkers and nucleic acid signal amplification strategies.Then the development and application of two-dimensional nanomaterials especially black phosphorus in biomedicine were introduced.In Chapter 2,an isothermal cascade HCR-DNAzyme signal amplification system with a theoretical signal amplification efficiency of n×N² was designed for the in situ detection of micro RNA biomarkers in extracellular vesicles(EVs).EVs from different type of cells are distinguished by their different expression levels of mi RNA.By simply introducing an auxiliary hairpin for target recognition,the integrated CHCR-DNAzyme signal amplification system can be expanded into a universal detection platform.Theoretically,the detection platform can be used to detect the mi RNA expression of EVs and provide gist for early cancer diagnosis.In Chapter 3,an isothermal auto-replicating HCR-DNAzyme signal amplification system with a theoretical signal amplification efficiency of n×N^N was designed for high sensitivity detection and accurate intracellular localization of mi RNA tumor markers.The reaction mechanism of RHCR-DNAzyme system was studied in detail through experiments,and the reaction kinetics model was further established to study the reaction mechanism of the system at the molecular level.By simply introducing an auxiliary hairpin for target molecule recognition without any optimization of the self-replicating amplification module,the RHCR-DNAzyme system can be expanded into a universal detection platform for high sensitivity detection and in situ imaging of intracellular mi RNAs.In Chapter 4,Au NPs doped BPNs nanocomposite(Au NPs/BPNs)was successfully synthesized by in situ reduction of metal precursors on two-dimensional BPNs carrier with reducibility by itself.The morphology and surface properties of Au NPs/BPNs could be controlled by simply adjusting the feed ratio between gold precursor and black phosphorus.Because of the cooperative effect between BPNs and Au NPs,the synthesised Au NPs/BPNs nanocomposite showed synergistically enhanced catalytic and antibacterial properties which could be adjusted by metal doping.The synergistic BPNs/Au NPs nanocomposite was studied in detail.In Chapter 5,a multifunctional BPNs/Mn O₂nanotheranostic platform with specific response to the tumor microenvironment(TME)was designed for T1-weighted MR imaging-guided synergistic photodynamic therapy/photothermal therapy.Among them,Mn O₂can not only enhance the photothermal conversion efficiency of BPNs,but also generate oxygen in the stimulation of tumor microenvironment and exhibit obviously decreased tumor hypoxia.In addition,the released Mn²⁺by degradation can be used as T1 contrast agent for the realization of MRI-guided enhanced tumor phototherapies.As an ideal drug carrier,BPNs/Mn O₂with a high specific surface was loaded with model drug DOX to construct a multifunctional BPNs/Mn O₂/DOX nanotheranostic platform.The DOX payload could be programmably released by endogenous TME and exogenous photothermal stimuli from the BPNs/Mn O₂/DOX platform,which could substantially enhance the anti-tumor therapy without undesired cytotoxicity during blood circulation.The results showed that the tumor-response MR imaging was achieved and the tumor was inhibited efficiently without recurrence.