Scientists say they have created an inexpensive system, using a smartphone and a lens made with an inkjet printer, that can detect lead in tap water at levels commonly accepted as dangerous. The system, described in the journal Analytical Chemistry, combines nano-colorimetry with dark-field microscopy, integrated into the smartphone microscope platform to detect levels of lead below the safety threshold set by the US Environmental Protection Agency (EPA). “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,” said Wei-Chuan Shih, an associate professor at the University of Houston in the US.
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, and Shih said currently available consumer test kits are not sensitive enough to accurately detect lead at that level. The latest application incorporates colour analysis to detect 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 an inexpensive smartphone with 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; the nanoparticles can be detected by combining colorimetric analysis and microscopy.
The analysis measured both 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, deionised 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, making it impossible to detect relatively low levels of lead. Building upon the smartphone microscope platform to create a useful consumer product was key, Shih said. “We wanted to be sure we could do something that would be useful from the standpoint of detecting lead at the EPA standard,” he said.