Synthesis And Biological Application Of Fluorescent Nanocomposites

When a substance continues to decrease in size until it falls below a certain critical size.The material will show a series of physical and chemical properties that are not originally available,such as surface effects,quantum size effects,volume effects,quantum tunneling effects,and the like.For most materials,this critical size is 100 nm,so materials below the critical dimension are collectively referred to as nanomaterials.There are different classification methods for nanomaterials.Accordingly,dimensions limited in the range of 1-100 nm,nanomaterials are classified as zero-dimensional nano-materials with all dimensions below 100 nm,and correspondingly,one-dimensional nanomaterials and two-dimensional nanomaterials could be define.Due to a series of adjustable properties,nanomaterials can be modified according to practical needs,thus promoting application in various fields such as optoelectronics,catalysis,biomedicine,analysis and detection.Among all nanomaterials,the zero-dimensional nanomaterials were first discovered in history because of their simpler synthesis protocol.Compared with other nanomaterials,zero-dimensional nanomaterials group possess the largest surface area,such material is best suited to add multiple functional groups at the same time.As a result,more and more research has focused on how to integrate multiple functions into the same zero-dimensional nanomaterials.For this purpose,the copper indium sulfide（CIS）quantum dots and silver nanoparticles（AgNPs）in zero-dimension are chosen as the research object.As a new class of light-emitting quantum dots,CIS has a band gap of 1.5 eV and a Bohr radius of 4.1 nm.It has a large extinction coefficient(α=5×10⁵ cm^-1)in the visible region.In addition to quantum size effect,its energy level structure can also be adjusted by changing the proportion of multiple components,which makes the fluorescence energy of CIS widely variable from the visible light to the near infrared.These properties make CIS a suitable material for optical and electronic applications.Compared with traditional quantum dots containing highly toxic elements,CIS has lower biological toxicity,cheaper raw materials.As traditional quantum dots are impeded in application mainly by toxicity,instead of already excellent opto-electric performance.Thus,CIS has become one of the most ideal alternative materials.In Chapter 2,we synthesized CIS quantum dots by one-pot method on the basis of previous report,and discussed the effects of synthesis time,ligand ratio and other factors on the optical properties of the products.The luminescence efficiency of CIS was enhanced by coating ZnS shells.Then,CIS was surface-functionalized with two different ligands:MUA and MTAB.Two kinds of water-soluble fluorescent quantum dots with different surface charge properties were prepared.MTAB-modified CIS successfully entered HeLa cells,without destroying them,realizing fluorescence imaging,which suggests CIS to be promising in biological application.The unique microenvironment of cancer cells is often used as a biomarker for potential tumor diagnosis and targeted tumor therapy.For example,the properties of cancer cells that are mildly acidic（pH 5.5-6.5）are widely used in the development of pH-responsive drug systems,through loading anti-cancer drugs that are initiated and released by low pH environments.On the other hand,cancer cells are characterized by a high H₂O₂ level（100μM-1 mM）,which is derived from the superoxide anion catalyzed by superoxide dismutase（SOD）in mitochondria.Highly toxic reactive oxygen species（ROS,such as·OH）produced by exogenous drugs can break the ROS homeostasis in tumor cells,leading to severe oxidative stress,thus apoptosis or death of cancer cells.In Chapter 3,we constructed a multifunctional fluorescent probe AgNPs-DNA@GO.The probe catalyzes decomposition of H₂O₂ and can simultaneously achieve fluorescence imaging and activity inhibition of cancer cells.Specific recognition of tumor cells is achieved based on the characteristics above.Double-stranded DNA is adsorbed on the surface of GO,and the probe is obtained by growing AgNPs using DNA as a template.Taking the advantages of water solubility,cell membrane permeability and biocompatibility,it has become a joint cancer monitoring system,with potential aiming for clinical treatment.