Application Of Organic Nanomaterials In Nonlinear Optical Imaging

Accurate imaging and treatment of biological tissues at the micro scopic scale is a major need in modern biomedical and clinical medicine.Fluorescence microscopy has been widely used in recent years,but the fluorescence emission process is often accompanied by problems such as fluorescence bleaching,photochemical toxi city,and fluorescence saturation.To address these issues,the researchers have set their sights on nonlinear optical imaging techniques.Second harmonic generation(SHG)is a branch of nonlinear optics whose processes do not absorb energy,circumventing the aforementioned problems posed by the fluorescent emission process of fluorescent dyes.And in SHG bioimaging,the tissue is pumped with near-infrared two-zone light with a deeper penetration depth.Therefore,the development of SHG imaging is an urgent need in the current field of bio-optical imaging.In order to increase the resolution and contrast of the images,the use of SHG nanoprobes to label living cells is the current common method.In recent years,large amounts of inorganic material have been prepared as SHG probes.However,considering the biocompatibility,targeting marker capability and metabolic properties,the potential for subsequent application of inorganic probes is not sufficient to compare with organic probes.In order to make second harmonic generation imaging an attractive tool,we developed RH237,DANS organic nanocrystals as SHG probes to be applied to imaging of living cells.The structure of nanocrystals can increase the orderly arrangement of organic molecules,improve the polarization rate of nanomaterials and increase the SHG signal.The preparation was carried out using the re-precipitation method,and a universal method for the preparation of organic nanocrystals with SHG properties was developed by adjusting the type of wrapping matrix,the feeding order and mass ratio of organic molecules to wrapping matrix.The prepared organic nanocrystals were characterized in a series of ways such as particle size,morphology,absorption-emission spectra,and nonlinear optical properties.The structure of the organic nanocrystals not only increases the SHG signal,but also greatly reduces the fluorescence emission signal by aggregation-caused quenching effect.Organic nanocrystals applied to SHG bioimaging of human breast cancer cells.The organic nanocytes were swallowed into the cells by co-incubation.Nonlinear optical imaging studies of living cells under a multi-photon microscope.In the SHG receiving channel,a bright and easily identifiable signal is observed;in other channels(including the two-photon fluorescence emission receiving channel),no signal or only a faint signal is observed.In this dissertation,the application of organic nanocr ystals to SHG imaging of living cells is realized,which expands the method of preparation of media materials and property regulation for nonlinear optical imaging,and provides a solid foundation for the future research of SHG imaging with deep tissue penetration and SHG excited photodynamic therapy.