An indicator-displacement assay based on the Murexide-Hg2+ system for fluorescence turn-on detection of biothiols in biological fluids

In this paper, we present a novel, rapid and sensitive sensor for biothiols including detection of glutathione (GSH), cysteine (Cys) and homocysteine (Hcy) based on an indicator displacement assay (IDA) for turn on the fluorescence of Murexide-Hg 2+ system. In this IDA approach, a commercially available dye, murexide (Mu), using as the indicator and selective detection of biothiols was achieved based on the competition between the indicator and biothiols for the binding with Hg 2+ . The fluorescence of Mu could be quenched in the presence of Hg 2+ due to the coordination between the indicator and Hg 2+ . Subsequently, the fluorescence of the Mu-Hg 2+ system was recovered gradually with the addition of biothiols such as GSH, Cys or Hcy due to their stronger affinity with Hg 2+ . A good relationship was obtained from 0.1–40   μM for GSH, from 0.5–30   μM for Cys and from 0.5–50   μM for Hcy, respectively. This method has been successfully applied to the trace detection of GSH, Cys and Hcy in human urine and serum samples with satisfactory results. Remarkably, the sensing process is able to be observed by the naked eye under UV irradiation which provides an instrument-free platform for point-of-care monitoring.