1. Background Introduction
Biochemical sensing technology is an important method for studying various chemical reaction processes and principles of life phenomena in complex biological environments by acquiring important chemical and biological information in biological systems. Selective molecular recognition enables detection of targets without the need for complex sample system separation. Based on the photophysical and photochemical characteristics of fluorescent molecules, fluorescence probes can be combined with fluorescence imaging technology to perform real-time monitoring of target activity in specific biological systems on a molecular scale. The detection objects of fluorescence probes mainly include various ions, small molecules, free radicals, peptides, enzymes, and it can also detect some indicators, such as temperature, pH, viscosity, etc. With the help of fluorescence imaging technology, fluorescence probes can detect real-time concentration and structure changes of target objects in living cells, can obtain various relevant information of biological tissues in life activities, and can also realize fluorescence imaging of living organisms. Fluorescence probe has gradually become an important tool in the research of the principles of life phenomena, disease diagnosis, and bio-molecule detection. The design and bioimaging application of fluorescence probe have also attracted a number of attentions in cross-disciplinary research fields.
2. Research Significance
Fluorescence probe technology can play an important role in the field of biochemical sensing. With the development of science and technology in relevant fields, it also puts forward higher requirements for the performance of fluorescence probe, and there are also many problems in the application areas. According to the principle of photochemical reaction, the recognition mechanisms of fluorescence probe mainly include: photoinduced electron transfer (PET), internal charge transfer (ICT), monomer-excimer, fluorescence resonance energy transfer (FRET), aggregation-induced emission (AIE). At present, fluorescence probe systems used in related international research fields are mainly based on materials such as biological fluorescent proteins, inorganic luminescent nanomaterials, fluorescent polymer nanoparticles, and fluorescent small molecules. Finding and constructing new fluorescence probe material systems with high sensitivity, high stability, recognition specificity, high quantum yield, good water solubility and biocompatibility, is necessary for research and application of biochemical technology. This subject intends to obtain fluorescence probe architectures with excellent comprehensive properties by designing, selecting, and synthesizing novel luminescent materials, and to provide theoretical and practical basis for the development of fluorescence probe technology.
3. Research Topics
3.1. Design and application of fluorescence probe system based on PET
A typical PET system is constructed by connecting a fluorophore with an electron donor-contained receptor through a spacer. In the fluorescence probe of this system, the fluorophore is used as a place to absorb excitation light and emit fluorescence. The main role of the recognition group is to bind to the target object or respond to related indicators. The two parts are separated by a spacer group while they are connected to form a supramolecule structure, which can obtain the effect of selective recognition of the target and selective response of related indicators, thereby giving a change in the fluorescence signal. In the PET-based fluorescence probe, there is a PET process from the recognition group to the fluorophore, which can induce strong quenching effect on the fluorescence. Therefore, when the fluorescence probe is not bound to the target object or does not reach the corresponding environmental indicator, the fluorescence probe emits very weak or even no fluorescence; when the recognition group binds to the target object or the environment reaches the corresponding indicator, the PET process is inhibited or completely blocked, and thus the fluorophore can get strong fluorescence emission. Before and after the target binding or related indicator is reached, the fluorescence intensity is very different, showing obvious fluorescence “on-off” phenomenon. Therefore, the detection of the fluorescence “on-off” state can be used to achieve sensing function.
3.2. Design and application of fluorescence probe system based on ICT
In a typical ICT-based fluorescence probe, a strong electron-pushing group and a strong electron-withdrawing group are respectively connected to a fluorophore, and the three are conjugatedly connected to form a strong push-pull electron system. When under excitation, a charge transfer occurs from the electron donor group to the electron acceptor group. In general, the recognition group in the ICT fluorescence probe will serve as the electron donor or acceptor group in the push-pull electron system. When it binds to the target object or reaches relevant environmental indicator, the push-pull electron system will be affected, causing change in emitted photon energy. This effect can be reflected in changes in the fluorescence emission spectrum, so that the sensing effect can be achieved by detecting the change in the emission color of the fluorescence probe.
3.3. Design and application of fluorescence probe system based on monomer-excimer
When two identical fluorophores are connected to the appropriate position of the same acceptor molecule, they can construct a monomer-excimer fluorescence probe system. When under excitation, it will form an intramolecular excimer between one excited fluorophore with another fluorophore that is still in the ground state, which can generate a new emission spectrum different from the fluorophore monomer. This new fluorescence peak position can be red-shifted, located in the long-wavelength-band, and has a wide spectral shape without fine structures. Since the formation of an intramolecular excimer requires an appropriate distance between the excited state fluorophore and the ground state fluorophore, the change in this distance can obviously determine whether the luminescence of excimer can occur, so that fluorescence probe system can be constructed. When the receptor molecule of the fluorescence probe is bound to the target or it is in the relevant environmental indicator, the change in the distance between the excited state and the ground state fluorophore can cause a significant change in the spectrum of the fluorescence probe. Thus detection of spectral signal changes can obtain sensing function of fluorescence probe.
3.4. Design and application of fluorescence probe system based on FRET
In the FRET-based fluorescence probe, when the distance between the energy donor fluorophore (D) and the energy acceptor fluorophore (A) is much larger than the collision diameter of D-A, non-radiative energy transfer from D to A may occur as long as there is an effective overlap between the emission spectrum of D with the absorption spectrum of A. To obtain this kind of FRET energy transfer process, it need to ensure that the fluorophore molecules have a proper arrangement in addition to satisfying the spectral overlap between the two. When A is a fluorophore and D is under excitation, the fluorescence emission of A will be observed due to energy transfer; when A is a quenching group, the change in fluorescence intensity of D can be observed. Therefore, when the fluorescence probe is bound to the target or is in the relevant environmental indicator, the arrangement of the fluorophore molecules will be affected, so that the fluorescence emission will change accordingly. Therefore, the fluorescence change of the fluorescence probe can be detected to achieve the role of obtaining relevant biochemical information.
3.5. Design and application of fluorescence probe system based on AIE
In recent years, with the discovery of molecules with AIE effect, it also provides a new way for the design and preparation of fluorescence probe materials with high brightness and high luminescence stability. This research area has also attracted much attention of related field to achieve high performance fluorescence probe. In contrast to the phenomenon of aggregation-induced fluorescence quenching, this material has almost no fluorescence emission in its lower concentration solution, but shows strong fluorescence in its solid or aggregation state. By introducing groups with AIE effect on the structure of water-soluble conjugated polymer, new fluorescent compounds with AIE effect can be obtained, and functional fluorescent nanoparticles can be further prepared and applied to biological detection. The design and preparation of materials with AIE effect provides an effective method to construct fluorescence probe system.
4. Research Schedule
2019.1-2019.12 | Synthesize novel luminescent materials with high performance; |
2020.1-2020.12 | Design and select suitable luminescent materials, and construct novel fluorescence probe system; |
2021.1-2021.12 | Verify the application method and performance of the novel fluorescence probe in biochemical sensing. |
5. Expected Outcomes
1) Organizing and completing an internationally cooperated research project;
2) Applying for 5 patents;
3) Publishing 10 SCI-collected papers;
4) Educating doctoral and graduate students.