Colorimetric chemosensor for Zn2+ based on pyrogallol red and poly(diallyldimethylammonium chloride) in aqueous solution

We report a new sensing strategy for Zn2+ by a colorimetric chemosensor based on commercially available negatively charged pyrogallol red (PR) and positively charged poly(diallyldimethylammonium chloride) (PDADMAC) ensemble in perfect aqueous solution at pH 7.0. The addition of ten equivalents of PDADMAC to PR resulted in PR aggregation by electrostatic interactions with PDADMAC. PR and PDADMAC ensemble showed a selective and distinct color change from red to blue in the presence of Zn2+ over other competitive metal ions. The color change was clearly visible to the naked eye, corresponding to a large red shift in the absorption peak from 544 to 595 nm. This result indicated that the PR and PDADMAC ensemble can serve as a potential candidate of a naked-eye chemosensor for Zn2+ in aqueous solution. This study demonstrates that the combination of organic dyes and oppositely charged polyelectrolytes is a versatile and useful tool, and shows great potential for the determination of important analytes in environmental and biological systems.