Nonlinear Optical Property Studies And Bioimaging Applications Of Aggregation-Induced Emission Materials

With the development of modern optical bio-imaging technology, the synthesis of new type fluorescent probes, the study of materials’novel optical properties and the design of advanced optical imaging systems have drawed more attentions in recent decades. The aggregation-induced emission (AIE) materials with their unique emission properties have become a useful fluorescent probe for bio-imaging applications in recent years. In this work, based on three different AIE fluorescent probes, we studied their multi-photon and other nonlinear optical properties, designed a new multi-photon fluorescence imaging system, and finally achieved their functional imaging applications in cells, tissue, in vivo blood vessels and zebrafish.In the first part, we studied TPE-TPP’s multi-photon fluorescence properties and used TPE-TPP as a fluorescent probe for the comparison of 1020nm-fs laser excited three-photon luminescence (3PL) imaging and 810nm-fs laser excited two-photon luminescence (2PL) imaging. We then concluded that the TPE-TPP-assisted 3 PL imaging take the advantages of low photobleaching, low photodamage, high spatial resolution and high signal to background ratio. Finally, we achieved the TPE-TPP-assisted 3PL imaging for the realtime, long-term, high sensitivity monitoring of membrane potential changes in mitochondria.TPE-TPP is also a suitable fluorescent probe for tracking neural cells and brain-microglia. By microinjection, we successfully achieved the realtime 2PL imaging of TPE-TPP labeled in vivo mouse brain-microglia under the excitation of 740nm-fs laser. Furthermore, the tissue imaging showed that 3PL imaging can achieve higher imaging effect, and it can be a promising technique for in vivo deep brain neural activity research.In the second part, based on TTF with long π-conjugated molecular structure, we studied its nonlinear optical properties (two-, three-, four-photon fluorescence, third, fifth harmonic generation) in different states, including dissolved in polar organic solvent, solid film and nano aggregation state. We also presented two new theories of "Third harmonic generation (THG) induced 3PL" and "Aggregation-induced THG enhancement" for the first time. TTF-doped-nanoparticles (TTF-ORMOSLIL and TTF-PEG) were further used for multimodal nonlinear optical microscopic imaging of cells, as well as 3PL in vivo imaging of mouse brain vessels.In the third part, we introduced a new synthesis method of TTF nanoparticles by the surface modification of nano graphene oxide (NGO). The synthesized TTF-NGO nanoparticles were stable and size tunable as well as emission efficiency enhanced. We then achieved 3PL bioimaging of ear blood vessels in mouse and the distribution of nanoparticles in zebrafish with the help of TTF-NGO nanoparticles. Furthermore, we extended this method to other AIE luminogens and showed that it was widely feasible.