Colorimetric detection of pyrophosphate in aqueous solution by pyrogallol red-based Zn²⁺ complex in the presence of poly(diallyldimethylammonium chloride)

The pyrogallol red-based Zn²⁺ complex (PR-Zn²⁺) between commercially available anionic dye, pyrogallol red (PR), and Zn²⁺ in the presence of cationic poly(diallyldimethylammonium chloride) (PDADMAC) was applied to the colorimetric recognition of pyrophosphate (PPi) in a pure aqueous solution under physiological pH. Upon the gradual addition of PPi to PR-Zn²⁺, the distinct color change from blue to pink could be recognized with the naked eye accompanied by a hypsochromic shift from 600 to 550 nm in the absorption spectra, indicating that PR was released from PR-Zn²⁺ through the interaction of PPi with Zn²⁺. No significant absorption spectral and color changes were observed in the presence of other anions including ATP and ADP with the structure similar to PPi. Moreover, other coexisting anions cause little or no interference to the detection of PPi. The results showed that PR-Zn²⁺ in the presence of PDADMAC could be a good naked-eye and colorimetric chemosensor for selective detection of PPi in aqueous solution. This study demonstrates that the combination of an organic dye, an oppositely charged polyelectrolyte, and a metal ion is a potential candidate for the easy construction of a new chemosensor system.