A highly selective chemosensor for colorimetric detection of Hg2+ and fluorescence detection of pH changes in aqueous solution

A naturally existing and unmodified simple chemosensor, 2-hydroxy-1,4-naphthoquinone (2HNQ), was identified and used for both the colorimetric detection of Hg2+ and the fluorescent (on-off) detection of pH. The distinct color change and quenching of fluorescence emission was visible to the naked eye. More importantly, the chemosensor was used in combination with β-cyclodextrin (β-CD), which enabled the sensor to be solubilized and stabilized in aqueous solutions. The sensor selectively detected Hg2+ via the stable 1:1 complexation of the CåO and OH groups with Hg2+ and reflected pH changes in the range from 6 to 12 via a fluorescence on-off response resulting from the deprotonation of the hydroxyl group in 2HNQ.