New molecule detects lead

Turquoise glow could reveal poisonous pollutant.
18 June 2002

TOM CLARKE

Lead poisoning can cause brain damage. © Hot Ideas/Alamy

A molecule that glows turquoise when it sticks to lead could be a new detector for the poisonous metal pollutant. It could help monitor lead levels in water supplies, or track the molecule's effects on the body.

"Fluorescence is more sensitive and much easier," than today's long, complicated lead tests, says Chao-Tsen Chen at the National Taiwan University in Taipei, who built the new molecule with colleague Wan-Pei Huang. The duo call their prototype 'chemosensor 1'.

Lead is an industrial pollutant from smelters and battery manufacture. The main sources used to be the burning of fuel with lead additives and house paint, though these were banned in the West in the 1970s and 80s. Prolonged exposure to low levels, can lead to memory loss, mental retardation, behavioral problems and anaemia especially in children. Higher levels can cause seizures, coma and death.

Lead levels in water supplies and in houses with old paintwork are monitored regularly. But only sophisticated laboratories can carry out the complex tests to detect low, but potentially dangerous, levels of the metal.

Chemosensor1 is based on two oft-used molecules: a crown-shaped one into which metal ions fit and a fluorescent chemical that glows brighter under certain conditions. Sensors for calcium and zinc contain similar compounds.

Using this technology for lead, says chemosensor pioneer Anthony Czarnic of Sensors for Medicine and Science, Inc. is "quite remarkable." Lead, a heavy metal, is renowned for stopping fluorescent molecules from working. The new compound glows 40-times brighter in the presence of lead ions.

Currently, chemosensor¹ is almost insoluble in water. Whether or not it is toxic to human cells, or whether it can even get into them, has not yet been tested.

If it can be made water soluable, the molecule will be ideal for monitoring lead in water supplies, says Czarnic. Some water mains already contain electronic sensors that monitor chorine levels round the clock. Fluorescent molecules incorporated into a light-sensing device could do the same for lead, he suggests.

If researchers could develop a non-toxic form of chemosensor1 that can pass through the cell membrane it could probe what lead does inside the body. "There is no existing sensor for lead inside cells. This might be turned into one," says Czarnic.

1. Chen, C-T & Huang, W-P.A highly selective fluorescent chemosensor for lead ions. Journal of the American Chemical Society, 124, 6246 - 6247, (2002).