Colorimetric detection of Cu 2+ using of a mixture of ponceau 6R and a cationic polyelectrolyte in aqueous solution

A colorimetric chemosensor is reported for Cu2+ by a simple mixture of two commercially available reagents, ponceau 6R (P6R) and poly(diallyldimethylammonium chloride) (PDADMAC) in an aqueous solution. P6R interacted electrostatically with PDADMAC to form the self-aggregate of P6R and exhibit a different sensing capability from P6R alone. The mixture showed high sensitivity and specific selectivity for detection of Cu2+ compared with various physiological and environmentally important metal ions. The addition of Cu2+ caused a hypsochromic shift with a distinct color change from red to yellow. While, upon adding Cu2+ to P6R alone, the solution underwent no distinct color change. The binding mode of P6R with Cu2+ was determined to be a 2:1 stoichiometry from Job plot and Cu2+ titration experiments. The results provide an easy method for developing new colorimetric sensors for metal ions by a combination of anionic dyes and cationic polyelectrolytes.