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Glutathione (GSH) probes can be used for qualitative and quantitative analysis of glutathione through specific binding of reaction recognition sites. GSH is a non-protein mercaptothiol composed of three amino acids, cysteine (Cys), glutamate (Glu) and glycine (Gly). These three kinds of small molecule biomercaptan have the same active site (sulfhydryl group), and combined with the fluorescent probe method, many GSH fluorescent probes with high specificity and sensitivity were developed.
Characteristics of Glutathione (GSH) Probes
The thiol group (-SH) on the structure of glutathione has strong nucleophilic property, so most fluorescent probes of glutathione have groups that recognize each other with the thiol structure. When the probe contacts with the thiol group, irreversible addition reaction or bond breaking reaction will occur, resulting in changes in the fluorescence signal of the environment where the probe is located, thus playing a role in recognition.
Classification of Glutathione (GSH) Probes
Common glutathione (GSH) probes can be divided into the following categories according to the reaction recognition sites on GSH probes.
- Oxygen/sulfide bond type glutathione probes
The mercapto functional group on GSH is prone to nucleophilic substitution reaction with the fluorophore that connects the oxygen/sulfide bond. Due to the large spatial structure, the rearrangement reaction cannot occur, resulting in the formation of sulfur-substituted products. This results in changes in environmental fluorescence signal, which enables highly selective fluorescence imaging of intracellular GSH.
- Sulfonates/sulfonamides type glutathione probes
Sulfonate bond or sulfonamide bond is easy to break under the nucleophilic action of mercaptan sulfhydryl group. Therefore, the method of connecting sulfonate bond or sulfonamide bond with fluorophore can be applied to construct biological mercaptan responsive GSH probe.
- Disulfide bond type glutathione probes
Disulfide bond (S-S bond) is a relatively stable form of covalent bond, which widely exists in the polypeptide and protein structure of life. There is a redox dynamic balance between free sulfhydryl and disulfide bonds in organisms. Therefore, the exchange reaction between biological sulfhydryl and disulfide bonds can be used to construct GSH fluorescent probes.
- Carbon / halogen bonds type glutathione probes
Taking advantage of the strong nucleophilic ability of the active sulfhydryl group of biological mercaptan, halogen atoms (such as Cl, Br) can act as the reaction site of sulfhydryl group to have nucleophilic substitution reaction with mercaptan. Using the unique performance of thioether and amino substitution fluorescent products with different spectral characteristics, GSH can be specifically detected.
- Selenium nitrogen bond type glutathione probes
Ebselenide is a glutathione peroxidase analogue, which can be used as a lipid peroxide radical scavenger. At the same time, it can react specifically with free sulfhydryl groups, which is due to the selenium nitrogen bond in the structure. Therefore, using this reaction mechanism, some thiol fluorescent probes based on Se-N bond have been developed.
- Unsaturated double bonds type glutathione probes
The sulfhydryl group of biological mercaptan has strong nucleophilic property and is easy to react with unsaturated bond receptor. This reaction characteristic has been widely used in the design and development of GSH specific fluorescent probes. These receptors mainly include maleimide, acryloyl, nitroene and other structures with unsaturated double bonds. The sulfhydryl group of GSH will attack and add to the double bond site, which will change the conjugate structure of the probe molecule, and then cause the change of fluorescence signal to achieve the purpose of detection.