Chromogenic sensing of biological thiols using squarylium dye

• A new biothiol probe SQ was synthesized.
• The probe displayed a color change from Cys, Hcy and GSH.
• SQ was highly selective for Cys detection.
• SQ could serve as a “naked-eye” probe for Cys with a minimum concentration of approximately 4 μM.

A new highly selective probe for biothiols, squarylium dye (SQ), was designed and synthesized. The probe displayed a color change from blue to colorless upon reaction with biothilos such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH). The competition experiments revealed that no obvious interference was observed by performing the titration with the mixtures of Cys and other amino acids. The results indicated that SQ was highly selective for Cys detection. Moreover, SQ could also serve as a “naked-eye” probe for Cys with a minimum detectable concentration of approximately 4 μM.

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