Researchers at the University of Houston have created an inexpensive system that can detect lead in tap water at levels commonly accepted as dangerous, using a lens made with an inkjet printer and a smartphone.
The system builds upon earlier work by Wei-Chuan Shih, associate professor of electrical & computer engineering, and members of his lab, including the discovery of an inexpensive elastomer lens that can convert a basic smartphone into a microscope.
The current project combines nanocolorimetry with dark-field microscopy, integrated into the smartphone microscope platform to detect levels of lead even below the safety threshold set by the Environmental Protection Agency.
According to the researchers, smartphone nano-colorimetry is rapid, low-cost, and has the potential to enable individual citizens to examine lead content in drinking water on-demand in virtually any environmental setting.
Even small amounts of lead can cause serious health problems, with young children especially vulnerable to neurological damage. EPA standards require lead levels in drinking water to be below 15 parts per billion. By using a smartphone equipped with an inkjet-printed lens and using the darkfield imaging mode, researchers were able to detect lead concentrations at 5 parts per billion. The sensitivity reached 1.37 parts per billion in deionized water. The application uses color analysis to detect these nanoscale lead particles.
The researchers built a self-contained smartphone microscope that can operate in both fluorescence and dark-field imaging modes and paired it with a Lumina 640 smartphone that has an 8-megapixel camera. They spiked 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 the lead to form lead chromate nanoparticles, which can be detected by combining colorimetric analysis and microscopy.
The analysis measured the intensity detected from the nanoparticles, correlating that to the lead concentration, and verified that the reaction was spurred by the presence of lead. The mixture was transferred to a polydimethylsiloxane slab attached to a glass slide; after it dried, deionized water was used to rinse off the chromate compound and the remaining sediment was imaged for analysis. The microscopy imaging capability proved essential, Shih said, because the quantity of sediment was too small to be imaged with an unassisted smartphone camera.