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Analytical Chemistry

Smartphone Attachment Detects Ionic Mercury

Water Analysis: With the snap of a picture, a new device could screen for the toxic metal

by Puneet Kollipara
January 29, 2014

Even Smarter Phone
Credit: ACS Nano
A new smartphone attachment allows researchers to measure mercury ion concentrations in water samples by snapping a picture.
Photograph of a smartphone sporting a new attachment for water testing.
Credit: ACS Nano
A new smartphone attachment allows researchers to measure mercury ion concentrations in water samples by snapping a picture.

A new attachment for smartphones allows scientists to measure levels of ionic mercury, Hg2+, in water just by snapping a couple of pictures. The device could provide a quick, portable screening tool for the toxic metal (ACS Nano 2014, DOI: 10.1021/nn406571t).

Scientists worry about Hg2+ levels because the ions can damage people’s kidneys, and, in the environment, microbes can convert them into methylmercury, a neurotoxic compound that accumulates in fish that people eat. Currently, researchers detect ionic mercury in water with spectroscopic methods, which use equipment that is expensive and isn’t portable. Aydogan Ozcan of the University of California, Los Angeles, and his colleagues thought a smartphone-based device would solve both problems.

Their detection method involves adding a water sample to a salt solution containing gold nanoparticles and single-stranded nucleotides called aptamers. The aptamers envelop individual gold nanoparticles, keeping them separated from each other. But if the water sample contains Hg2+, the mercury ions bind to the aptamers, stripping them from the nanoparticles. The gold particles then start to clump, causing the light they emit to shift from red to blue. As the mercury ion concentration increases, so does the shift in the solution’s color.

The researchers use this shift to measure the Hg2+ concentration. They insert two tubes of the nanoparticle-aptamer solution into the smartphone attachment: one with the mercury-tainted water sample and one without. The apparatus shines red and green light onto the tubes and directs the light transmitted by the nanoparticle solutions toward the phone’s camera. A smartphone application determines the Hg2+ concentration based on color differences between pictures of the two tubes.

The technique can detect Hg2+ levels as low as 3.5 ppb, which is less sensitive than traditional methods but is close to the Environmental Protection Agency’s drinking water limit of 2 ppb. Ozcan says they possibly could improve the detection limit by shining more colors of light on the nanoparticle solutions.

Mercury Spotting
Schematic for mercury sensing method using gold nanoparticles.
Credit: ACS Nano
To detect ionic mercury in water, researchers add the water samples to a solution of gold nanoparticles (red, left) coated with DNA aptamers (blue lines). The mercury ions (orange circles) bind to these aptamers, pulling them away from the nanoparticles (right). The gold nanoparticles then clump up and change their color from red to blue. A new attachment for smartphone cameras allows researchers to analyze this color change to determine the water sample’s mercury content.


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