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The discovery of lead in Flint, Michigan's drinking water, has drawn renewed attention to the health risks posed by the metal. Now, researchers at the University of Houston have created an inexpensive system using a smartphone and a lens made with an inkjet printer capable of detecting lead in tap water at levels generally considered dangerous.
The system builds on the earlier work of Wei-Chuan Shih, associate professor of electrical and computer engineering, and members of his lab, including the discovery of an inexpensive elastomer lens capable of converting a smartphone from base in microscope.
The last discovery, described in the review Analytical Chemistry, combines nano-colorimetry with darkfield microscopy, integrated with the smartphone's microscope platform to detect lead levels below the safety threshold set by the Environmental Protection Agency .
"The nano-colorimetry of smartphones is fast, inexpensive and can allow individual citizens to examine the lead content of drinking water on demand in virtually any environment," wrote Researchers.
Even small amounts of lead can cause serious health problems, as young children are particularly vulnerable to neurological damage. EPA standards require lead levels in drinking water of less than 15 parts per billion, and Shih said currently available consumer test kits are not sensitive enough to accurately detect lead at this level.
Using an inexpensive smartphone equipped with an ink jet printed lens and using dark field imaging mode, the researchers were able to produce a system that was both portable and easy to use, capable of detecting lead concentrations of 5 parts per billion. in the tap water. The sensitivity reached 1.37 parts per billion deionized water.
Shih and his students last year released an open-source dataset Biomedical Optical Express, explaining how to convert a smartphone equipped with the elastomer lens into a fluorescence microscope. This document has been the most downloaded article of the journal since its publication.
The latest application incorporates color analysis to detect lead particles at the nanoscale. In addition to Shih, the project's researchers include first author Hoang Nguyen and Yulung Sung, Kelly O 'Shaughnessy and Xiaonan Shan, all in the Department of Electrical and Computer Engineering at UH. (O 'Shaughnessy was a summer intern at the University of Cincinnati as part of the National Science Foundation's research experiment program.)
Applying the dataset published in 2017, the researchers built a stand-alone smartphone microscope that can work in both fluorescence and dark field imaging mode and associated with an inexpensive Lumina 640 smartphone with a camera of 8 megapixels. They added tap water with varying amounts of lead, ranging from 1.37 parts per billion to 175 parts per billion. They then added chromate ions, which react with lead to form lead chromate nanoparticles; Nanoparticles can be detected by combining colorimetric analysis and microscopy.
The analysis measured both the intensity detected by the nanoparticles, the correlation with the lead concentration and verified that the reaction was stimulated by the presence of lead.
The mixture was transferred to a polydimethylsiloxane plate attached to a glass slide; after drying, deionized water was used to rinse the chromate compound and the remaining sediment was imaged for analysis.
Microscopic imaging capacity has proven essential, said Shih, because the amount of sediment was too small to be imaged with an unattended smartphone camera, making it impossible to detect relatively low levels of lead. .
According to Shih, it is essential to rely on the microscopic platform of the smartphone to create a useful consumer product. "We wanted to make sure we could do something that would be useful from the point of view of lead detection at the EPA standard," he said.
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