The Research Of Nanobubbles Manipulated By Substrates And Its Effect On Protein Activity

It was proved that aggregation behavior of gases at nanometer scale on the solid-liquid interface has an important effect on the properties of solid-liquid interface.Also,It has wide potential application in many fields,such as surface chemistry,colloid chemistry,fluid dynamics,environmental and life sciences researches and drawn great attentions from researchers.How to explain the stable mechanism of the existence of the interfacial nanobubbles and the larger contact angle compared with the macroscopic contact angle of droplet are the controversial questions and also the key issues of the current research needed to be solve urgently.The study of surface nanobubbles is inseparable from the substrate.In theory,the two key issues above are directly related to the substrates used to produce surface nanobubbles,so the nature of the substrate is one of the key factors and should not be ignored.On the one hand,the formation?stability and interface morphology of bubbles may be different on various substrates;on the other hand,the contact angles may also vary with the nature difference of the substrate.In consideration of the single substrate used by researchers to produce nanobubbles and the poor controllability and unrepeatability in nanobubble generation,it is urgent to develop a new method to further study the basic physical properties?formation mechanism and stability mechanism of nanobubbles by controlling the surface structure and properties of the substrates.Based on the above purposes,this thesis uses Electron Beam Lithography(EBL)to prepare periodic substrates with different structures and hydrophobicity to produce nanobubbles with ethanol-water exchange.The AFM images of nanobubbles on these nanostructured substrates indicated that nanobubbles were mainly adsorbed on the hydrophobic regions of the periodic structures and were limited by the the hydrophobic structure,causing the change of contact angles.At the same time,the corresponding molecular dynamics simulation has further supported the restriction effect.This would provide the experimental basis for exploring the application of nanobubbles in the development of microfluidic devices and manipulating nanobubble generation.Biological inert gas exert its effects by combining with some biomolecules or ion channels and thus play an important role in many life processes,such as biological anesthesia,nerve and tissue protection,but people know little on its internal mechanism.Molecular dynamics studies have found that aggregated nitrogen molecules can specifically bind to the active site of the protein,whereas free nitrogen molecules do not have this specific binding effect.With the discovery of nanobubbles,there seems to be a new way for understanding its mechanism.The inert gas molecules can specifically bind to the hydrophobic group of protein molecules in the form of nanobubbles,inhibiting biological functions of protein,which restored when the gas is removed.Based on this idea,we detected the fluorescence adsorption of Xe and Kr in pepsin solution by micro X-ray fluorescence absorption spectroscopy and fluorescence imaging techniques at BL15U in Shanghai Synchrotron Radiation Facility.The results showed that the concentration of Xe and Kr in pepsin solution is higher than that without pepsin.The nanoparticle tracking results showed that the concentration of particles in the Xe-containing pepsin solution was higher than that of the non-Xe-containing pepsin solution,which may be due to the fact that the Xe molecule binds to the pepsin to form larger particles.Molecular dynamics results showed that different gas molecules can be specifically aggregated as bubbles on the pepsin molecule.The related protein activity experiments also showed that the addition of N2,Xe,Kr in pepsin solution,the protein activity decreased,after degassing treatment,protein activity recovery.This provides an effective way for us to understand the biological effects of gas molecules in depth.