THESIS
2020
xxviii, 170 pages : illustrations (chiefly color) ; 30 cm
Abstract
Fluorescence have found wide scope of application in biological science and
biomedical field since its discovery, due to the real time, in situ and non-invasive
characteristics. Molecules that emit fluorescence is called fluorophores or luminogens.
Organic fluorophores have been widely used in biological applications. However, most
organic fluorophores are not soluble in water and they trend to form aggregates in water
or biological fluids. Unfortunately, traditional organic fluorophores suffer from
aggregation-caused quenching (ACQ) effect. That means, their fluorescence intensity is
decreased or even quenched after forming aggregates. In this situation, the ACQ
fluorophores are often used in dilute solution, which limit the usage in some situations.
In 2001, Tang et. al. disc...[
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Fluorescence have found wide scope of application in biological science and
biomedical field since its discovery, due to the real time, in situ and non-invasive
characteristics. Molecules that emit fluorescence is called fluorophores or luminogens.
Organic fluorophores have been widely used in biological applications. However, most
organic fluorophores are not soluble in water and they trend to form aggregates in water
or biological fluids. Unfortunately, traditional organic fluorophores suffer from
aggregation-caused quenching (ACQ) effect. That means, their fluorescence intensity is
decreased or even quenched after forming aggregates. In this situation, the ACQ
fluorophores are often used in dilute solution, which limit the usage in some situations.
In 2001, Tang et. al. discovered an opposite phenomenon to the ACQ. There are a group
of fluorophores that are not emissive in dilute solution as separated molecule and become
highly emissive after forming aggregates or presence in the solid state, which is termed
Aggregation-induced emission (AIE). The most widely accepted mechanism of this
phenomenon is the restriction of intramolecular motion (RIM). Guided by the RIM
mechanism, many AIE luminogens (AIEgens) have been designed to show great potential
in the application of biosensing, bioimaging and image-guided therapy
Owing to the AIE effect, the aggregates of AIEgens used in biological fluid show
intensive fluorescence and photosensitization. Thus, AIE aggregates can be used in some
biomedical applications with better performance than commercial ACQ dyes. In this
thesis, AIEgens are used as highly emissive luminogenic aggregates in various
applications. Due to the high photostability, organelle specific AIEgens are used in
multiplexed imaging to monitor the changes under apoptosis. Under excessive reactive
oxygen species (ROS) such as hydrogen peroxide, cells will undergo apoptosis. The
changes of organelles during apoptosis are clearly monitored.
Apart from fluorescence, the generation of ROS by organic photosensitizer is also
influenced by the aggregate formation. Therefore, AIE photosensitizer also shows high
efficiency of ROS generation in the aggregate state. Photodynamic therapy (PDT) is to
use photosensitizer to generate large amount of ROS which caused the apoptosis or
necrosis of cells and thus it is used in cancer treatment, especially the skin cancer. The
fluorescence-guided cancer cell ablation and melanoma treatment were achieved by
rational design of mitochondrion targeting and near infrared emission AIE photosensitizer.
If a fluorophore has high fluorescence quantum efficiency and photostability, the
usage of its fluorescence as spectra shifting would be possible. The oxygenic
photosynthesis is the primary usage of light energy. The responsible part of light energy
harvesting and usage contains biological pigments. Those pigments absorb widely in the
visible light, however, have relatively little absorption in the short wavelength region.
The incubation of AIE nanoaggregates efficiently convert the light energy that is less
useful into the photosynthetic active light, leading to the dramatically enhanced
photosynthesis and growth of cyanobacteria.
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