Colorimetric detection of cysteine by surface functionalization of natural cellulose substance

Immobilization of ruthenium dye–Hg2+ complex (N719–Hg2+ complex) monolayer on ultrathin zirconia gel film coated cellulose nanofibers of filter paper was conducted to fabricate a solid-phase sensing device with high sensitivity, selectivity and reversibility for colorimetric detection of Cys in aqueous media. This assay relies on the specific mercury release by cysteine from the immobilized N719–Hg2+ complex. And the dissociation of N719 and Hg2+ caused by such mercury displacement engenders obvious orange-to-purple color change of the zirconia gel layer and N719–Hg2+ complex modified filter paper, hence realizing the colorimetric detection of cysteine. The detection limit of this assay is 20 μM by the naked eye and the selectivity for Cys against interference of the other 19 natural amino acids and their mixture is extremely high.