With the continuous development of biological science and technology, people gradually transition from cellular level to subcellular level to understand and study the nature of life activities. Because of its high sensitivity and responsiveness, small molecule fluorescent probes have become an advantageous means for the study of subcellular structures. The organelle probe locates in the subcellular structure by the recognition group, so as to make the cell structure image, and then track the position and morphological changes of the cell structure in real time.
Organelle fluorescent probes are widely studied according to the different cell substructures they act on, including endoplasmic reticulum-targetable fluorescence probes, mitochondria-targetable fluorescent probes, lysosome-targetable fluorescence probes and so on.
- Endoplasmic reticulum-targetable fluorescence probes: As an important organelle, endoplasmic reticulum (ER) is responsible for the transport of substances in cells, and is also the synthesis base of proteins, lipids, sugars, etc. Therefore, it is of great significance to track the changes of ER configuration and the levels of various active small biological molecules in real time. Meinig  synthesized a fluorescent probe located in the endoplasmic reticulum (see Figure 1) and modified part of the ammonia substituents. The fluorescence intensity of fluorophore was high, the quantum yield was 0.85 (ex.512 nm, EM.532 nm), and the fluorophore could be specifically located in the endoplasmic reticulum of living HeLa cells.
Fig.1 The structure of endoplasmic reticulum-targetable fluorescence probe 
- Mitochondria-targetable fluorescent probes: Mitochondria, as key energy supply cells, also participate in cell metabolism and apoptosis. A large number of studies have shown that the number, distribution and structure of mitochondria are related to neurodegenerative diseases, metabolic diseases, cardiovascular diseases and other diseases. Therefore, it is of great significance to conduct localization imaging of mitochondria and to study the active molecules in mitochondria. Xing  successfully labeled sialic acid monosaccharides (see Fig.2) by clicking chemistry using a cyanine dye (Cy3/Cy5), Cell imaging experiments showed that the probe was located in mitochondria of PC-12 cells, and it is a kind of mitochondrial probe with good water solubility.
Fig.2 The structures of cyanine labeled membrane targetable fluorescent Probes 
- Lysosome-targetable fluorescence probes: As an important acidic organelle in eukaryotic cells, when the number and distribution of lysosomes are abnormal due to the variation of lysosomes or the influence of the outside world, it may cause lung disease, lysosome storage disease, tumor and other diseases. In order to effectively detect the distribution and reaction process of lysosomal active molecules, we designed and synthesized a series of lysosomal targeted fluorescent probes based on organic small molecules, which can be used as research tools for imaging lysosomal active molecules in cells, tissues and organisms.
Fig.3 Rhodamine-based probes in the lysosome: structures and responsing reactions 
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- Meinig, J. M.; et al, Synthesis of Fluorophores that Target Small Molecules to the Endoplasmic Reticulum of Living Mammalian Cells. Angew. Chem., 2015,54, 9696.
- Zhang, X. T.; et al, Synthesis and labeling of α-(2,9)-trisialic acid with cyanine dyes for imaging of glycan-binding receptors on living cells. Chem. Commun. 2015, 51, 8606.
- Huang, R.; et al, A lysosome-targeted fluorescent sensor for the detection of glutathione in cells with an extremely fast response. Chem. Commun. 2016, 52, 11579.