Researchers have fabricated a sensitive sensor that can detect minute traces of mercury in water1. The sensor is based on natural-polymer-modified gold nanoparticles and is potentially useful for monitoring mercury concentrations in the environment, water and foodstuffs.
Coal-based power plants and metal-refining plants release mercury into the environment, where bacteria convert it into methylmercury. Methylmercury then accumulates in the tissues of marine animals and plants, including edible fish. If eaten in sufficiently large quantities, mercury-contaminated food can cause neurological disorders in humans.
Existing mercury sensors require complex and expensive instruments. To devise a simple, cost-effective and ecofriendly mercury sensor, the researchers synthesized gold nanoparticles by using carboxymethylagarose, an Indian seaweed-derived natural polymer.
To investigate the mercury-sensing efficacy of the gold nanoparticles, the researchers exposed them to different solutions containing mercury and other metal ions. They then studied the absorption spectra of the nanoparticles in ambient conditions before and after the addition of 100 parts per million (ppm) aqueous solutions of mercury and other metal ions.
The nanoparticles exhibited a blue appearance when exposed to a solution containing mercury ions. On increasing the mercury concentration, the colour of the solution changed to light purple and then to dark orange. The researchers found that the nanoparticles needed to be exposed for 10 minutes to detect mercury ions in water. In addition, they found that the nanoparticles could detect mercury ions in real samples, such as lake water spiked with 10 ppm mercury ions.
The nanoparticles retained their mercury-sensing efficiency even after being refrigerated for more than five months. The nanoparticles can also be reused, making this process cost effective. “These nanoparticles could potentially be used to make mercury sensor that can work at neutral pH and detect mercury concentrations between 0.01 ppm and 100 ppm,” says Ramavatar Meena, a senior author of the study.
