Self-Assembly of Graphene Oxide with a Silyl-Appended Spiropyran Dye for Rapid and Sensitive Colorimetric Detection of Fluoride Ions

Fluoride ion (F-), the smallest anion, exhibits considerable significance in a wide range of environmental and biochemical processes. To address the two fundamental and unsolved issues of current F- sensors based on the specific chemical reaction (i.e., the long response time and low sensitivity) and as a part of our ongoing interest in the spiropyran sensor design, we reported here a new F- sensing approach that, via assembly of a F--specific silyl-appended spiropyran dye with graphene oxide (GO), allows rapid and sensitive detection of F- in aqueous solution. 6-(tert-Butyldimethylsilyloxy)-1',3',3'-trimethylspiro [chromene-2,2'-indoline] (SPS), a spiropyran-based silylated dye with a unique reaction activity for F- was designed and synthesized. The nucleophilic substitution reaction between SPS and F- triggers cleavage of the Si-O bond to promote the closed spiropyran to convert to its opened merocyanine form, leading to the color changing from colorless to orange-yellow with good selectivity over other anions. With the aid of GO, the response time of SPS for F- was shortened from 180 to 30 min, and the detection limit was lowered more than 1 order of magnitude compared to the free SPS. Furthermore, due to the protective effect of nanomaterials, the SFS/GO nanocomposite can function in a complex biological environment. The SPS/GO nanocomposite was characterized by XPS and AFM, etc., and the mechanism for sensing F- was studied by H-1 NMR and ESI-MS. Finally, this SFS/GO nanocomposite was successfully applied to monitoring F- in the serum.