A fluorescent probe molecule usually consists of a Fluorophore and a Receptor connected by a covalent bond via a Spacer. Fluorophore can be used as a signal converter to transform the recognition behavior into light signal, which can be used to recognize analytes by fluorescence enhancement or quenching or even spectral shift change. Fluorescent probe molecules have great plasticity and application potential. Through modification of organic molecular structure, fluorescent probe can be designed and synthesized to meet various needs. Fluorescent probes have been widely used in clinical analysis, environmental monitoring, biological analysis and life science due to its small size, low cost, no need for pretreatment and no influence of external electromagnetic field and become an important research hotspot.
Fig.1 Second Near-Infrared fluorescent probe stem cell labeling
Fluorescent probes are widely studied and used due to their high sensitivity and specificity. According to the different targets and parts of the probes, they can be divided into ion probes, organelle fluorescence probes, membrane potential probes and other probes.
- Ion Probes: Anions and metal cations all play an important role in the maintenance of ecological balance both in nature and in life. Their content is closely related to the physiological and pathological state of human body and the degree of environmental pollution, but these ions are basically trace, so it is more difficult to detect them. Therefore, due to their strong specificity and high sensitivity, the ionic fluorescent probes have emerged and been widely used in ion detection, such as Ca2+, Zn2+, Hg2+, Al3+, Cl-, ClO- and so on. Recently, Kan designed a novel probe (see Fig.2) for the detection of Al3+ in water and fluorescence imaging in breast cancer cells.
Fig.2 Recognition mechanism of Al3+ probe
- Organelle fluorescent Probes: With the rapid development of fluorescent labeling and molecular probes, fluorescent probes have become an important method to study the subcellular structure. Thus, a variety of organelle probes have been studied and used more and more widely. For example, D'Amore synthesized a fluorescent probe NRB-AF12, which can label Endoplasmic reticulum with highly selective ang low cytotoxicity. Chen has designed and synthesized a near-infrared lysosomal probe, it can be used not only for the detection of HNO in RAW264.7 cell lysosomes, but also for nitrosyl hydrogen imaging in mice without background fluorescence interference.
Fig.3 Organelle probe examples
- Membrane potential probes：Membrane potential probe provides an indirect and convenient method for detecting the transmembrane potential of the plasma membrane, enabling researchers to make membrane potential measurements in organelles and cells that are too small for microelectrodes, which can then be used for imaging. The increase and decrease of membrane potential play a central role in many physiological processes, including the transmission of nerve impulses, muscle contraction, cell signal transduction, and ion channel gating. These probes can be used in vivo, in perfusion organs, and in the brain to map cell membrane potential changes at spatial resolution and sampling frequency not available with microelectrodes.
Fig.4 Mitochondrial membrane potential imaging
- Other Fluorescent Probes: In addition to the types of fluorescent probes mentioned above, there are many other types of fluorescent probes that have been designed and synthesized to use their specificity to reveal and explore life processes at different levels. For example, protein fluorescence probe can be used to better study protein conformation, structural properties and protein interactions. Quantum dot probes based on nanomaterials have higher luminescence intensity than ordinary fluorophores and have attracted extensive attention in the fields of analytical detection and biomedical tracer imaging.
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- Yejun, Z.; et al, Recent Advances in Tracking the Transplanted Stem Cells Using Near-Infrared Fluorescent Nanoprobes: Turning from the First to the Second Near-Infrared Window. Advance Healthcare Materials, 2018, 20(7).
- Kan, C.; et al, A new reversible fluorescent chemosensor based on rhodamine for rapid detection of Al (III) in natural environmental water samples and living organisms. Tetrahedron Letters, 2020, 61 (42): 152407.
- Hui.; et al, Recent progress on endoplasmic reticulum-targetable fluorescence probe. Chin. J. Org. Chem. 2018, 38, 3165-3175.
- Lingxin Chen.; et al, Visualization of nitroxyl (HNO) in vivo via a lysosome-targetable near-infrared fluorescent probe.Chem. Commun. 2014, 50, 14253.