Study On Photoluminescence Effect Of Single Nanoparticles Based On Evanescent Wave Excitation

The properties of each particle can be obtained by the study of single nanoparticles,which contributes to explore structure-activity relationships in a "bottom-up" approach.Single nanoparticles study is of great significance for rational design and construction of new high-efficiency nanomaterials,thus promoting its applications in nano-sensing and nano-catalysis.The interaction between nanomaterials and light is the basis for its wide applications in photocatalysis and plasmon optics.Taking quantum dots as an example,quantum dots absorb energy to generate electrons and holes under certain light.In addition to the heat dissipation process associated with the non-radiative transition,the carriers generated by photoexcitation either combine to form optical radiation and release energy(the fluorescence process),or undergo electron transfer with molecules that coexist in the system to trigger chemical processes(the photochemical process).There is a competitive relationship between the two processes,so it is possible to study electron transfer or chemical processes by monitoring changes in photoluminescence signals.According to this idea,the total internal reflection fluorescence microscope is used to image and measure the fluorescence characteristics of the semiconductor quantum dots and the surface enhanced Raman scattering characteristics of the noble metal nanoparticles,in order to provide a method for evaluating the chemical reaction activity via the single particle photoluminescence behavior.This thesis is divided into three chapters altogether.The first chapter is an introduction.It briefly introduces the basic knowledge of total internal reflection fluorescence imaging technology,single molecule fluorescence blinking and blinking surface enhanced Raman scattering.The first part is about the principle,uniqueness and application of total internal reflection fluorescence imaging.The second part introduces the single molecule fluorescence blinking,the discovery and mechanism of quantum dots fluorescence blinking,and data processing methods(including ICS and power-law).The third section outlines the development of blinking surface-enhanced Raman scattering and focuses on its blinking mechanism.In the second chapter,the total internal reflection inverted fluorescence microscope was used to observe and analyze the changes of CdSe/ZnS QDs fluorescence blinking before and after adding ascorbic acid and nickel nitrate,and then to explore the chemical reaction activity of CdSe/ZnS QDs with ascorbic acid and nickel nitrate.On the macroscopic steady state,the fluorescence spectrum analysis showed that the fluorescence intensity of the quantum dot solution added with ascorbic acid or nickel nitrate decreased to varying degrees,and the fluorescence of the quantum dot solution added with ascorbic acid and nickel nitrate decreased the most.The microscopic fluorescence imaging analysis showed that with the increase of the concentration of the reaction liquid and the increase of the laser power,the fluorescence intensity of the whole quantum dots in the image decreased and the probability density of the quantum dots in the off-time increased.By analyzing the fluorescence intensity of individual quantum dots in the field of view at different concentrations,it was found that each quantum dot had significant individual difference in response concentration.The quantum dots with regular fluorescence blinking reacted sharply when the concentration of the reaction solution was low,while the quantum dots with messy fluorescence blinking need higher concentration to be more obvious.The difference in reactivity of quantum dots may be related to their surface structure.This experiment indirectly reflects the chemical reaction activity by monitoring the changes of the fluorescence blinking of single quantum dots,and provides a novel reference method for the screening of specific chemical reactivity materials.In the third chapter,the blinking surface enhanced Raman scattering signal of the silver nanoparticle aggregates under the evanescent wave was observed by the combination of the total internal reflection fluorescence microscope and the imaging spectrometer.The spectrum showed no fluorescence peak after the three-dimensional fluorescence scanning of the steady-state spectrometer,and the SEM characterization of the silver nanoparticles in the experiment was compared with the luminescence characteristics on the optical microscope.It was found that the particles with strong luminescence intensity and high blinking frequency correspond to the aggregates in SEM,which showed the same characteristics as surface enhanced Raman scattering.With the use of a spectrometer attached to one end of the microscope,the measured Raman spectral peak intensity and position of individual silver nanoparticle aggregates fluctuated,and differ from fluorescence blinking in that only the intensity fluctuates.This result further confirmed that the surface enhanced Raman scattering signal of silver nanoparticles aggregates was observed in the experiment.The spectra of the silver nanoparticles in this experiment are compared with the Raman spectra of sodium citrate under the laser confocal Raman microscope.Most of the spectral peaks can be matched,and we can obtain the conclusion that the surface enhanced Raman scattering signal is derived from the surface adsorbed citrate anion.The Raman spectra in this study were measured using a semiconductor laser under wide-field excitation of an evanescent wave.In general,Raman spectra are measured using an argon ion laser under confocal excitation,which has significant differences.The method of surface enhanced Raman scattering spectroscopy developed in this study is simple and fast,and can simultaneously obtain Raman spectra of multiple particles,which is highly efficient and provides a new method for wide-field imaging of single particle Raman spectroscopy.