A fluorescent sensor for detecting mercury in water has been developed by US researchers.   

The Mercury Sensor 4 (MS4), developed by Elizabeth Nolan and Stephen Lippard at the Massachusetts Institute of Technology, is a seminaphthofluorescein (SNAFL)-based dye that shows a change in fluorescence intensity when mercury is present in solution.   

In addition to being soluble in water and showing positive fluorescence when it coordinates with Hg(ii), MS4 is also selective towards a number of other metal ions. 

Heavy metal pollution, and mercury contamination in particular, is a significant global problem. Mercury enters the food chain as a result of bioaccumulation in, for example, fish, which are then eaten by humans. Neurological problems in humans have been linked with this kind of mercury contamination.   

There is a real need, therefore, to develop improved methods for detecting environmental mercury. Nolan and Lippard say that water-soluble small molecule fluorescent mercury sensors are 'one powerful option' for doing just that. 

A Prassana de Silva, from Queen's University, Belfast, said of Nolan and Lippard's development, 'This is the first fluorescent ratiometric sensor for Hg(ii) in near-neutral solution and it cleverly exploits the known ratiometric pH sensor SNAFL'. 

In future Nolan and Lippard hope to use the sensors to detect mercury in water samples and biological tissues. But they warn that developing procedures for using these sensors in these environments 'will require substantial effort'. Katherine Davies