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Mercury and Methylmercury: detect and discriminate

Environmental pollution due to mercury takes a huge toll on human health. Excess consumption of mercury ions can cause organ failure and even death.

The solubility of methylmercury ions in lipids facilitates crossing biological membranes and even the blood-brain barrier. Thus, it gets deposited in the brain and kidney, making it more toxic than mercury ions. It was methylmercury that was responsible for the famous case of Minamata disease in Japan.

There are several methods to detect mercury ions. But detecting the more toxic methylmercury still poses challenges. 

Nilanjan Dey from BITS Pilani, Hyderabad recently designed a simple strategy for the visual detection of mercury and methylmercury. He considered the phenanthroline moiety, or part, as his starting point.  Phenanthroline, a fluorescent molecule with more than one aromatic ring, is known for its affinity to mercury.

Nilanjan used a reaction between phenanthroline, 1,10-phenanthroline-2,9-dicarbaldehyde and isoniazid to create an amphiphile – a compound with both hydrophilic and lipophilic properties. The amphiphile of phenanthroline spontaneously formed nanoaggregates.

Both the species of mercury reacted with the fluorescent nanoaggregates, destabilising the nanoassembly and enabling a charge transfer interaction. So, on adding mercury or methylmercury ions, the nanoaggregates changed from colourless to yellow. 

“The fluorescent property also changed”, says Nilanjan.

There was a 12-fold decrease in fluorescence at 465 nanometres with mercury ions. But, with methylmercury ions, only a four-fold fluorescence quenching was observed. 

“Methylmercury ions are larger and have lower charge density. So they take longer than mercury ions to interact with the phenanthroline unit. The colour change and reduction in fluorescent intensity are also slower”, explains Nilanjan.

Nilanjan coated paper strips with the material and tested water from a tap, a pool and the sea for mercury contaminants. The change in colour was easily observable. And, when a UV torch was shone, the quenching of blue fluorescence was even more apparent.

“This is a cost-effective solution to test wastewater and drinking water for mercury contamination,” he says. 

Nilanjan then tested the compound for detecting mercury in human serum. And, after testing the toxicity of the compound, he went on to detect mercury inside HeLa cells.

“The material could detect both the toxic forms of mercury in water, in serum and within cells”, he claims. 

Since it is low cost and is highly sensitive and selective to mercury, Nilanjan hopes that the material he designed will one day become the mainstay for mercury contamination testing.

DOI: 10.1039/d1dt01455b

Amrit Krishna Mitra
Government General Degree College, Singur

STEAMindiaReports: Detecting useful scientific papers and reporting them
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Editor’s note:

This report was written during an online workshop on science writing organised by Current Science. The details of the next online workshop on science writing can be accessed here.

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Categorised in: Ecology, Environment, Nanotechnology, Telengana, Water

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