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Detecting Bismuth Pollution: A fluorescent chemosensor

Bismuth, a moderately priced metal, has various applications in alloys and cosmetics as well as in the electrical and fire industries. Compounds based on bismuth are also useful in medicine, as anti-HIV, anti-ulcer, antimicrobial and diuretic drugs.

Bismuth crystals. The colours are due to formation of thin layers of bismuth oxide on the metallic crystals.
Image: Maxim Bilovitskiy via Wikimedia Commons

However, consuming bismuth in excess has acute and chronic effects such as delirium, psychosis, ataxia and seizures. So we need a method to detect and estimate bismuth ions in food and water. 

Recently, researchers from Karunya Institute of Technology and Sciences and Amrita School of Engineering in Coimbatore collaborated to develop sensor for the purpose.

They considered 2-pyridine carboxaldehyde, an aromatic compound with an affinity for bismuth. To detect the association of the compound with bismuth, they thought of linking the pyridine compound with 1,5-diaminonaphthalene, which is known to be a good donor and acceptor of electrons by internal rearrangements. The intramolecular electron transfers can be detected using fluorescence. 

“When these two compounds are coupled, they become a Schiff base. And Schiff bases have been used for detecting metal ions”, explains R Nandhakumar, Karunya Institute of Technology and Sciences.

So, the researchers started experimenting.

To a dry ethanolic solution of 1,5-diaminonaphthalene, they added 2-pyridine carboxaldehyde drop by drop, stirring it all the while. They filtered and cleaned the product, dissolved it in methanol and recrystallised it. And the sensor was ready: yellowish green microcrystals.

They tried to confuse the sensor, testing it in a mixture containing many different ions. Shine 370 nanometre wavelength light, and the solution will fluoresce at 415 nanometres, if bismuth is not present. But if there is bismuth in the solution, then fluorescence shifts to 399 nanometres.

 “We used the sensor to detect bismuth ions in water and food samples.  And we could even map intra-cellular bismuth ions in bacterial cells using cell tagging fluorescence imaging,” says T G Satheesh Babu, Amrita School of Engineering.

“The sensor is reusable. We could remove the bismuth bound to the sensor using a chelating agent”, says A Abiram, Karunya Institute of Technology and Sciences.

So now we have a simple tool for biologists to pinpoint the location of bismuth in cells. And a cost-effective tool in the environmentalist’s kit for detecting bismuth pollution in the ecosystem.

DOI: 10.1016/j.jphotochem.2021.113558

Amrit Krishna Mitra
Government General Degree College, Singur

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