ALL CHEMISTS ARE FAMILIAR WITH the litmus test. Like other acidbase indicators, litmus changes color when the pH of a solution changes. The indicator is an example of a colorimetric ion sensor. In the presence of hydroxonium ions (H3OO, litmus is red, whereas in alkaline solution it is blue. Chemists at Trinity College Dublin (TCD) have now developed a family of naked-eye colorimetric anion sensors, which, they say, could potentially be used like litmus paper to check domestic water quality and for environmental and other applications. Naked-eye colorimetric sensors that detect anions in aqueous solution are few and far between, says Paul E. Kruger, senior lecturer in inorganic chemistry, who developed the sensors with associate professor of chemistry Triorfinnur Gunnlaugsson and coworkers at TCD (J. Org. Chem. 2005,70,10875). Kruger holds up a piece of blue litmus paper. Easy to use, commonly available litmus- paper-style oelorimetric tests for simple anions such as acetate, fluoride, and ...