A new type of fluorescent sensor for detecting mercury ions has been developed by scientists in the US. 

Mercury is a highly toxic metal that can cause serious health and environmental problems. A number of sensors have been developed for the detection of mercury but many are difficult to make or suffer from a lack of selectivity or sensitivity. 

Ling Zang and colleagues at Southern Illinois University, US, have designed an easy-to-make fluorescent sensor based on a perylene molecule modified with two thymine moieties. In the absence of mercury, the molecules fluoresce. If mercury ions are present, they bind strongly to the thymines leading to aggregation of the sensor molecules. This aggregation quenches the fluorescence. The sensor was able to detect mercury at concentrations lower than the safety level set for drinking water by the US Environmental Protection Agency. 

Zang tested the sensor with a number of other metal ions and found that no other ion quenched the fluorescence. He is delighted with the results. 

'This research has paved the way to develop a sensor assay, which will provide highly selective detection of mercury ions with minimal false positives,' said Zang. 'We expect that such an expedient sensing assay will find broad applications in both water environment monitoring and clinical diagnostics.' 

The sensor assay currently runs in a mixture of water and dimethylformamide. To aid practical application of the sensor, the next goal for Zang is to synthesise a water-soluble sensor so that the assay can be completely free of organic solvent. 

Joanne Thomson