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The development of a fluorescent probe to distinguish between cysteine (Cys) and homocysteine (Hcy) is always a challenge owing to their structural similarity, and the simultaneous detection of Cys and Hcy by utilizing different emission channels is especially difficult. In this work, we designed and synthesized a new fluorescent probe to differentiate between Cys and Hcy on the basis of a coumarin derivative with a chlorine atom and an α,β-unsaturated aldehyde. Cys and Hcy induced different cascade reactions with the probe, which led to different products with distinct photophysical properties. The nonfluorescent probe responded to Cys and emitted strong blue fluorescence, whereas it reacted with Hcy and generated yellow fluorescence without interference from glutathione. In addition, the probe was successfully applied to distinguish between Cys and Hcy in living cells. [ABSTRACT FROM AUTHOR]

A fluorescent probe ( 1 ) for distinguishing amongst biothiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), is developed based on different cascade reactions. The key design feature of fluorescent probe 1 is the integration of two potential reaction groups for the thiol and amino groups of biothiols in one molecule. By reacting with the halogen atom and α, β-unsaturated malonitrile in probe 1 , Cys, Hcy and GSH can generate a total of three main products with distinct photophysical properties. Probe 1 shows a strong fluorescence turn-on response to Cys with blue–green emission by using an excitation wavelength of 390 nm. At an excitation wavelength of 500 nm, probe 1 responds to GSH over Cys and Hcy and emits strong orange fluorescence. The discrimination of biothiols can be demonstrated by cell imaging experiments, indicating that probe 1 can be a useful tool for the selective imaging of Cys and GSH in living cells. [ABSTRACT FROM AUTHOR]