From Local Surface Plasmon-enhanced Fluorescence Spectroscopy To Single-Molecule Spectroscopy

With the development of nano-science and technology,surface-enhanced Raman and fluorescence spectroscopy as the important parts of PES draw lots of attention.The Raman and fluorescence spectroscopy of molecules could provide abundant information about molecules' figure print and electron transition,which serves as a strong analysis technique to the deep understanding of the inner mechanism of chemical reactions.Therefore,the research based on plasmon-enhanced spectroscopy(PES)is of great significance for the development of ultra-sensitive surface interface analysis techniques.To obtain the optimal enhancement effect and deep understanding of the interactions between the plasmon and molecules,it is necessary to construct a welldefined and effective system for plasmon research,then,we can precisely regulate the resonance of plasmon and the interaction between of them.Therefore,the design of plasmonic nanostructures has become important research in PES.However,it remains a challenge to fully understand the enhancement process and mechanism of the plasmon effect because of the difficulties in achieving reliable and accurate plasmon nanostructures.In this thesis,we mainly focus on the SERS and SEF to investigate the interactions between the plasmon and matter and precisely regulate the plasmon resonances.The detailed plots are in the following:(1)Shell-isolated nanoparticles were used to enhance the molecular fluorescence on the surface of the graphene substrate.The fluorescence enhancement was achieved by a factor of nearly 100K by adjusting the shell thickness of nanoparticles and different coupling modes,and then the enhancement was explained by combining theoretical calculation.(2)The effective design of the plasmon nanostructures depends on the understanding of the coupling hotspots.Given that graphene has a large scattering cross-section and a low fluorescence background,it is used as a molecular probe in the nanometer gap.By combination with experiments and theories,we achieved nanoscale resolution of the electromagnetic field in the nano-cavity.(3)The effective regulation of the resonance frequency of the plasmon provides an effective platform for studying of PES technology.Ag nanometer cubes and gold substrates are used to establish the plasmon nanocavities,and the continuous regulation of the plasmon resonance frequency in visible and near-infrared regions is realized through the regulation of the nanometer gap and the change of particle sizes.(4)SERS and SEF technology plays an important role in fully understanding the interactions between plasmonic nanocavity and molecules.The probe molecules were placed at different nanocavities to achieve fluorescence enhancement up to 5000 times.when the probes were located in different positions of the same cavity,we found that the SERS and SEF tendencies were different,and we concluded that the energy transfer effect was the main cause of its performance differences.(5)Single-Molecule(SM)spectrum information can reflect the virtual interaction between nanocavity and materials.The results showed that the drift of the real-time spectral peak phenomenon was resulted from the self-interaction of the molecule.And more,a new method to detect the excited state distribution of an SM in the nanometer cavity is proposed through theoretical simulation,which provides theoretical guidance for the in-depth understanding of the plasmon enhancement effect and the effective manipulation of light and matter in the nano-level.