Spiropyran-based optical approaches for mercury ion sensing: improving sensitivity and selectivity via cooperative...

Spiropyrans are an attractive starting point in design of optical approaches for metal ions sensing. However, the high background in aqueous solution and non-specific chelation of the spiropyran with heavy metal ions has hindered their application as reliable sensors for environmental and biological species. Here, we report on a new spiropyran-based approach for sensitive and selective sensing of Hg(2+) in aqueous solution, based on cooperative ligation interactions among the spiropyran probe, an intermediate, cysteine, and the metal ion. To test the feasibility of this design, three spiropyran scaffolds, L1-L3, with different ligation functions at the 8'-position were examined as model systems. The results demonstrate that by using cysteine, a potential ligand of Hg(2+), the spiropyran could detect 1.0x10(-7) M Hg(2+) in aqueous solution. Due to the specific metal-amino acid interaction, the approach exhibits selective response toward Hg(2+) over other metal ions and anions, although possible interference from Cu(2+) has to be considered at the high level of the metal ion. This approach has been used for the determination of Hg(2+) in water samples containing potential interferents with satisfactory recovery.